Subject: 8 Tech
------------------------------
Subject: 8.1 Technical Support Numbers
From: Joshua Putnam <Joshua_Putnam@happy-man.com>
[This list is now in the ftp archives as it is too long to put here]
------------------------------
Subject: 8.2 Ball Bearing Grades
From: Bill Codding <peda@simplicity.Stanford.EDU>,
Harry Phinney <harry@hpcvlx.cv.hp.com>
Following is a description of the different grades of ball bearings.
The grade specifies the sphericity of the balls in millionths of an
inch.
Thus, grade 25 are round to 25/10^6, while grade 1000 are good to 1/1000
(i.e. not all that round, but probably good enough for our uses).
Grade 25: the highest quality normally available, aka
"Campagnolo quality": hardened all the
way through, best
alloys, coatings, roundness, and durability.
Evidently,
a recent bottom-bracket overhaul article
in "Bicycling Plus
Mountain Bike" magazine recommended
these. Campy's tech reps
claim that the bearings in a set (usually
in a little paper bag)
are matched. One should not mix
bearings from different sets.
Grade 200: mid-range
Grade 1000: seems to be the lowest, may only be surface
hardened.
Good sources for ball bearings:
Your local bike shop (make sure you're getting the grade
you want)
Bike Parts Pacific
Bike Nashbar 1-800-NASHBAR ($1-$3
per 100 Grade 25)
The Third Hand 1-916-926-2600 ($4-$7 per 100 Grade
25)
------------------------------
Subject: 8.3 SIS Cable Info
From: Jobst Brandt <jbrandt@hpl.hp.com>
After Joe Gorin described the SIS "non-compressive" cable housing to
me I got myself a sample to understand what the difference is.
I
believe "non-compressive" is a misnomer. This cable housing is
NOT
non-compressive but rather a constant length housing. As far
as I can
determine, and from reports from bike shops, this housing should not
be used for brakes because it is relatively weak in compression, the
principal stress for brake housing.
SIS housing is made of 18 strands of 0.5mm diameter round spring steel
wire wrapped in a 100mm period helix around a 2.5mm plastic tube.
The
assembly is held together by a 5mm OD plastic housing to make a
relatively stiff cable housing. Because the structural wires
lie in a
helix, the housing length remains constant when bent in a curve.
Each
strand of the housing lies both on the inside and outside of the curve
so on the average the wire path length remains constant, as does the
housing centerline where the control cable resides. Hence, no
length
change. A brake cable housing, in contrast, changes length with
curvature because only the inside of the curve remains at constant
length while the outside (and centerline) expands.
Shimano recommends this cable only for shift control but makes no
special effort to warn against the danger of its use for brakes.
It
should not be used for anything other than shift cables because SIS
housing cannot safely withstand compression. Its wires stand
on end
and have no compressive strength without the stiff plastic housing
that holds them together. They aren't even curved wires, so they
splay out when the outer shield is removed. Under continuous
high
load of braking, the plastic outer housing can burst leaving no
support. Besides, in its current design it is only half as flexible
as brake cable because its outer shell is made of structurally stiff
plastic unlike the brake cable housing that uses a soft vinyl coating.
Because brake cables transmit force rather than position, SIS cable,
even if safe, would have no benefit. In contrast, with handlebar
controls to give precise shift positioning, SIS housing can offer some
advantage since the cable must move though steering angles. SIS
housing has no benefit for downtube attached shifters because the
cable bends do not change.
------------------------------
Subject: 8.4 Milk Jug Mud Flaps
From: Chuck Tryon <bilbo@bisco.kodak.com>
Actually, I have used plastic like this (or in my case, some
red plastic from a cheap note book cover -- it's heavier) to
extend the
bottom (rear) end of the front fender. The Zephals are
good, but they
don't stop the splash from where the tire hits the road from
getting on my
feet. What I did was cut a small triangle about 3in (~7cm)
wide by 6in
(~15cm) long, cut a hole in the top of it and the bottom end
of the fender,
and use a pop-rivet (with washers to prevent tear out) to attach
it. On a
road bike, it should be end up being within a few inches of
the road. ATB's
will need more clearance, so this won't work well off road.
| |
| |
/| o |\ <-----
rivet with washer on inside
| \___/ |
/
\ <---- flap fits inside of the fender, and follows the
|
| curve, which gives it some
stiffness.
|
|
|
|
\_________/
| |
| |
<----- bottom of tire
\_/
------------------------------
Subject: 8.5 Lubricating Chains
Lubricating chains is a somewhat religious issue. Some advocate
oil,
some Teflon-base lubricants, some paraffin wax. The net majority
favors
a lubricant that does not leave an oily coating on the chain that can
attract dirt, which will hasten chain/chainring/freewheel sprocket
wear.
If you want to use paraffin wax, make sure you melt the wax in a double
boiler! Failure to do so can lead to a fire. You can use
a coffee
can in a pan of boiling water if you don't want to mess up good cookware.
After the wax has melted, put the chain in the wax and simmer for 10
minutes or so. Remove the chain, hang it up, and wipe the excess
wax
off. Let it cool and reinstall on your bike.
When using a liquid lubricant, you want to get the lube onto the pins
inside the rollers on the chains, not on the outside where it does
little
good. Oilers with the narrow tubes are good for this because
you can put
the lube where you want it. Work the oil into the chain after
applying
it, wipe the chain off, and reinstall on your bike.
A good discussion of chain maintenance is at
http://www.sheldonbrown.com/chains.html
------------------------------
Subject: 8.6 Wear and Gear Slippage
From: Jobst Brandt <jbrandt@hpl.hp.com>
Chain wear and care seems to be a never ending discussion, especially
for new bicyclists who are not entirely happy with this dirtiest of
bicycle parts. This leads to the first problem, of whether there
is a
best (and cleanest) way to care for a chain. There are several
ways
to take care of a chain of which some traditional methods are the most
damaging to the chain and others work to prolong life.
At the outset the term "chain stretch" is misleading and wrong.
Chains do not stretch, in the dictionary sense, by elongating the
metal through tension. They lengthen because their hinge pins
and
sleeves wear. This wear is caused almost exclusively by road
grit
that enters the chain when it is oiled. Grit sticks to the outside
of
a chain in the ugly black stuff that can get on ones leg, but external
grime has little functional effect because it is on the outside where
it does the chain no damage. Only when a dirty chain is oiled,
or has
excessive oil on it, can this grit move inside where it causes damage.
Commercial abrasive grinding paste is made of oil and silicon dioxide
(sand) and silicon carbide (sand). You couldn't do a better job
if
you tried to destroy a chain, than to oil a dirty chain.
Primitive rule #1: Never oil a chain on the bike.
This means the chain should be cleaned of grit before oiling it and
because this is practically impossible without submerging the chain
in
a solvent bath (kerosene or commercial solvent), it must be taken off
the bicycle. Devices with rotating brushes, that can be clamped
on
the chain on the bicycle, do a fair job but are messy and do not
prevent fine grit from becoming suspended in the solvent. External
brushing or wiping moves grit out of sight, but mainly into the
openings in the chain where subsequent oiling will carry it inside.
Do not use gasoline because it is explosive and contains toxic light
petroleum fractions that penetrate the skin. Removing the chain
from
the bicycle isn't always possible. There are times (after riding
in
the rain) when a chain screams for oil and a good cleaning is not
practical. In that case rule #1 may be violated for humanitarian
reasons. However, only an internally clean chain squeaks, so
it isn't
as bad as it sounds. Also, water is a moderately good lubricant,
but
as soon as the rain stops, it evaporates.
Removing the solvent from the chain after rinsing is important.
Compressed air is not readily available in the household nor is a
centrifuge. Manually slinging the chain around outdoors works
best if
the chain is a closed loop but without pressing the pin completely
in.
The other way is to evaporate it. Accelerated drying methods
by
heating should be avoided, because they can be explosive.
Lubricating the chain with hot 90W gear lube works but it is also
efficient fly paper, collecting plenty of hardpack between sprockets
and on the outside of the chain. Motor oil is far better, but
motorcycle chain and chainsaw lubricants are better yet, because they
have volatile solvents that allow good penetration for their
relatively viscous lubricant. Paraffin (canning wax), although
clean,
works poorly because it is not mobile and cannot replenish the bearing
surfaces once it has been displaced. This becomes apparent with
any
water that gets on the chain. It immediately sqeaks.
Swaged bushing chains
Sedis was the first with its Sedisport chain to introduce swaged
bushings, formed into the side plates, to replace full width steel
bushings on which the rollers and pins bear. Although stronger
and
lighter than prior chains, it achieves its light weight at the expense
of durability. These chains, now the only derailleur chains
available, have only vestigial sleeves in the form of short collars
on
the side plates to support the roller on the outside and the link pin
on the inside. This design is both lighter and stronger because the
side plates need not have the large hole for insertion of sleeves.
Because MTB's use drive sprockets as small as 18t that can cause
extremely high chain loads, pin and sleeve chains could be at a
disadvantage to safely withstand such loads while shifting.
The pins inside full bushing chains were well protected against
lubricant depletion because both ends were covered by closely fitting
side plates. Some motorcycle chains have O-ring seals at each
end.
In the swaged bushing design there is no continuous tube because the
side plates are formed to support the roller and pin on a collar with
a substantial central gap. In the wet, lubricant is quickly washed
out of pin and roller and the smaller bearing area of the swaged
bushing for the pin and roller easily gall and bind when lubrication
fails. Although this is not a problem for this type of chain
when dry
it has feet of clay in the wet.
Chain Life
Chain life is almost entirely a cleanliness and lubrication question
rather than a load problem. For bicycles the effect of load
variations is insignificant compared to the lubricant and grit
effects. For example, motorcycle primary chains, operated under
oil
in clean conditions, last years while the exposed rear chains must
be
replaced often.
The best way to determine whether a chain is worn is by measuring its
length. A new chain has a half inch pitch with a pin at exactly
every
half inch. As the pins and sleeves wear, this spacing increases
and
this concentrates more load on the last tooth of engagement, changing
the tooth profile. When the chain pitch grows over one half percent,
it is time for a new chain. At one percent, sprocket wear progresses
rapidly because this length change occurs only between pin and sleeve
so that it is concentrated on every second pitch; the pitch of the
inner link containing the rollers remaining constant. By holding
a
ruler along the chain on the bicycle, align an inch mark with a pin
and see how far off the mark the pin is at twelve inches. An
eighth
of an inch (0.125) is a little over the one percent limit while more
than a sixteenth is a prudent time to get a new chain.
Skipping Chain
Sprockets do not change pitch when they wear, only their tooth form
changes. The number of teeth and base circle remain unchanged
by
normal sprocket wear.
A new chain often will not freely engage a worn rear sprocket under
load, even though it has the same pitch as the chain. This occurs
because the previous (worn and elongated) chain formed pockets in the
teeth by exiting under load. A chain with correct pitch cannot
enter
the pockets when its previous roller bears the previous tooth, because
the pocket has an overhang that prevents entry.
Without a strong chain tensioner or a non derailleur bicycle, the
chain has insufficient force on its slack run to engage a driven
sprocket. In contrast, engagement of a driving sprocket, the
crank
sprocket, generally succeeds even with substantial tooth wear, because
the drive tension forces engagement.
However, worn teeth on a driving sprocket cause "chainsuck", the
failure of the chain to disengage the chainwheel. This occurs
more
easily with a long arm derailleur, common to most MTB's, that is one
reason this occurs less with road racing bicycles, that experience
a
noisy disengagement instead.
In contrast a worn chain will not run on a new driving sprocket.
This
is less apparent because new chainwheels are not often used with an
old chain. In contrast to a driven sprocket (rear) the chain
enters
the driving sprocket under tension, where the previous chain links
pull it into engagement. However, because a used chain has a
longer
pitch than the sprocket, previous rollers bear almost no load and
allow the incoming chain link to climb the ramp of the tooth, each
successive link riding higher than the previous until the chain jumps.
The pockets in a used sprocket are small but they change the pressure
angle of the teeth enough to overcoming this problem.
Jobst Brandt <jbrandt@hpl.hp.com>
------------------------------
Subject: 8.7 Adjusting Chain Length
From: Bob Fishell <spike@cbnewsd.att.com>
For all Shimano SIS and Hyperglide systems, the chain is sized by shifting
to
the smallest rear cog and the largest front sprocket, then sizing the
chain so that the derailleur pulleys are on a vertical line, or as
close
as you can get to it. Note that this will result in the same
chain length
for any freewheel within the capacity of the derailleur, so it usually
is
not necessary to re-size the chain for a different cogset with these
systems.
The other rule I've used (friction systems) involves shifting to the
largest
chainring and the largest rear cog, then sizing the chain so that the
pulleys
are at a 45 degree angle to the ground.
The rules probably vary from derailleur to derailleur. In general,
you may use the capacity of the rear derailleur cage as a guideline.
You
want the chain short enough so the cage can take up the slack in the
smallest combination of chainwheel and rear cog you will use. The chain
must also be long enough so that the cage still has some travel in
the
largest combination you will use.
For example, if you have a 42x52 crank and a 13x21 freewheel, the smallest
combination you would use would be a 42/14 (assuming you don't use
the
diagonal). If the cage can take up the slack in this combo, it's short
enough.
If the cage has spring left when you are in the 52/19 combo (again,
you are
not using the diagonal), it's long enough.
------------------------------
Subject: 8.8 Hyperglide chains
For those of you that are tired of dealing with Shimano's
chains with the special pins, I've found that the following
chains work well with Shimano Hyperglide gearing systems:
DID SuperShift
Sedis ATB
Union 800
Union 915
The SuperShift is probably the best performer of the bunch,
followed by the ATB and 915. The 800 doesn't do too well
with narrow cogsets (i.e., 8-speeds) because the raised
elliptical bumps on the side-plates tend to rub on the adjacent
cogs.
I've also found that these chains work well on SunTour systems.
The 915, however, works better on PowerFlo cogs than it does
on regular (AccuShift) cogs (where it tends to slip when shifting).
------------------------------
Subject: 8.9 Bottom Bracket Info
From: Jobst Brandt <jbrandt@hpl.hp.com>
The four kinds of BB threads in common use today are Italian, British,
French, and Swiss, possibly in that order of occurrence.
Diameter
Pitch Right Left Cup
--------
----- ----- -----
Italian 36mm x 24F tpi
right right tpi (threads per
inch)
British 1.370" x 24F tpi left
right
French 35mm x 1mm
right right
Swiss 35mm x
1mm left right
Unless there is something wrong with the right hand cup it should not
be
removed but should be wiped clean and greased from the left side.
The
thread type is usually marked on the face of both left and right cups.
Swiss threads are rare but if you have one it is good to know before
attempting removal.
------------------------------
Subject: 8.10 Crank noises
From: Phil Etheridge <phil@massey.ac.nz>
I've had the creaky crank problem on every bike I've owned which has
had cotterless cranks. Until now, I've never known a good solution
to
the problem.
One suggestion I had was to replace the crank, but that wasn't
something I was prepared to do on 1 month old bike under warranty.
The shop mechanic spent half an hour with me and my bike sorting it
out. Tightening the crank bolts and pedal spindle (i.e. onto
the
crank) didn't help (as Jobst will tell you).
Removing each crank, smearing the spindle with grease and replacing
the crank eliminated most of the noise. Removing each pedal,
smearing
grease on the thread and replacing it got rid of the rest of the
noise.
Greasing the pedal threads is a new one on me, but it makes a lot of
sense, since they are steel and the crank aluminum. I thought
it was
worth relating this story, as creaky cranks seems to be quite a common
problem.
------------------------------
Subject: 8.11 Cracking/Breaking Cranks
From: Jobst Brandt <jbrandt@hpl.hp.com>
Since the advent of the crank cottage industry, crank failures have
become more common than previously because most of these "home made"
cranks, usually produced in prototype quantities on numerically
controlled (NC) milling machines, have not been designed with sound
engineering practices, nor have they been tested destructively in
repeatable tests on testing machines. My comments are mostly
aimed at
major brand production cranks.
Cranks break primarily because they are aluminum and because they have
high stress principally at two places. Aluminum has no distinct
fatigue threshold in contrast to steel, so that with increasing use
and load cranks are destined to break at the two most failure prone
places, the pedal eye, and the junction of the spider fingers and the
right crank.
The pedal eye is weak because the joint is incorrectly designed, but
being standard, it may not be changed since it appears to work.
This
joint always moves under load and through its fretting causes an
undercut in the face of the crank. Removal of a pedal, that has
been
ridden any considerable amount, will reveal a recess in the face of
the crank with cracks around its circumference caused by fretting.
The cracks often propagate into the crank and cause failure.
A
solution to this problem would be a 45 degree taper in place of the
flat shoulder at the end of the pedal thread.
The thin web between the crank and the adjacent legs of a five legged
spider is also a place where most cranks crack. The Campagnolo
C-Record as well as Ritchey cranks address this problem by using the
crank itself as the fifth leg of the spider, and transmitting pedal
torque directly from the crank to the chainwheels. By this
arrangement the spider merely supports the chainwheels radially and
laterally and the driving torque is delivered by a solid anchor.
------------------------------
Subject: 8.12 Biopace chainrings
Biopace chainrings have fallen into disfavor in recent years.
They
are hard to "pedal in circles". The early Biopace chainrings
were
designed for cadences of around 50-70 rpm, while most recommend a
cadence of 80-100 rpm. Newer Biopace chainrings are less elliptical,
but the general consensus is to (if you are buying a new bike) get
the
dealer to change the chainrings to round ones.
Sheldon Brown has some information on Biopage chainrings at
http://www.sheldonbrown.com/biz/hub/biopace.html.
------------------------------
Subject: 8.13 Snakebite flats
Snakebite flats are usually caused by the tire and tube being pinched
between the road and the rim, causing two small holes in the tube that
look like a snakebite. The usual causes are underinflation, too
narrow a tire for your weight, or hitting something (rock, pothole)
while having your full weight on the tire.
The obvious solutions are to make sure your tires are inflated properly,
use a larger size tire if you weigh a lot, and either avoid rocks and
potholes or stand up with your knees and elbows flexed (to act like
shock
absorbers) when you go over them.
------------------------------
Subject: 8.14 Blown Tubes
From: Tom Reingold <tr@samadams.princeton.edu>
Charles E Newman writes:
$ Something really weird happened
at 12:11 AM. My bike blew a
$ tire while just sitting parked in my room. I was awakened by a noise
$ that scared the livin ^&$% out of me. I ran in and found that
all the
$ air was rushing out of my tire. How could something like happen in
the
$ middle of the night when the bike isn't even being ridden? I
have
$ heard of it happening when the bike is being ridden but not when
it is
$ parked.
This happened because a bit of your inner tube was pinched between your
tire bead and your rim. Sometimes it takes a while for the inner
tube
to creap out from under the tire. Once it does that, it has nothing
to
keep the air pressure in, so it blows out. Yes, it's scary.
I've had
it happen in the room where I was sleeping.
To prevent this, inflate the tire to about 20 psi and move the tire
left and right, making sure no part of the inner tube is pinched.
------------------------------
Subject: 8.15 Mounting Tires
From: Douglas Gurr <dgurr@daimi.aau.dk>
A request comes in for tyre mounting tricks. I suspect that this ought
to be
part of the FAQ list. However in lieu of this, I offer the way it was
taught
to me. Apologies to those for whom this is old hat, and also for the
paucity
of my verbal explanations. Pictures would help but, as always, the
best bet
is to find someone to show you.
First of all, the easy bit:
1) Remove the outer tyre bead from the rim. Leave the inner bead.
Handy hint. If after placing the first tyre lever you
are unable to fit another in because the tension in the
bead is too great
then relax the first, slip the second in and use both
together.
2) Pull out the tube finishing at the valve.
3) Inspect the tube, find the puncture and repair it.
Now an important bit:
4) Check tyre for thorns, bits of glass etc - especially at the point
where
the hole in the tube was found.
and now a clever bit:
5) Inflate the tube a _minimal_ amount, i.e. just sufficient for it
to
hold its shape. Too much inflation and it won't fit inside
the tyre.
Too little (including none at all) and you are likely
to pinch it.
More important bits:
6) Fit the tube back inside the tyre. Many people like to cover the
tube in
copious quantities of talcum powder first. This helps
to lubricate
the tyre/tube interface as is of particular importance
in high pressure
tyres.
7) Seat the tyre and tube over the centre of the rim.
8) Begin replacing the outer bead by hand. Start about 90 degrees away
from
the valve and work towards it. After you have safely passed
the valve,
shove it into the tyre (away from the rim) to ensure that
you have
not trapped the tube around the valve beneath the tyre
wall.
Finally the _really_ clever bit:
9) When you reach the point at which you can no longer proceed by hand,
slightly _deflate_ the tube and try again. Repeat this
process until
either the tyre is completely on (in which case congratulations)
or the tube is completely deflated. In the latter case,
you will have
to resort to using tyre levers and your mileage may vary.
Take care.
and the last important check:
10) Go round the entire wheel, pinching the tyre in with your fingers
to check that there is no tube trapped beneath the
rim. If you
have trapped the tube, deduct ten marks and go back
to step one.
Otherwise ....
11) Replace wheel and reinflate.
------------------------------
Subject: 8.16 More Flats on Rear Tires
From: Jobst Brandt <jbrandt@hpl.hp.com>
Date: Thu, 22 Jan 1998 18:15:42 PST
Many sharp objects, especially those that lie flat on the road like
nails and pieces of metal, more often enter rear tires than the front
tires. That is because the front tire upends them just in time
for
the rear tire to be impaled on them.
For example, nails seldom enter front tires. When dropped from
a
moving vehicle, nails slide down the road, and align themselves
pointing toward traffic, because they prefer to slide head first as
they would when laid on a slope. The front tire rolling over
such a
lengthwise nail, can tilt it up just in time for the rear tire to
encounter it on end. I once got a flat from a one inch diameter
steel
washer that the front tire had flipped up so that the rear tire struck
it on edge. When following another wheel closely, the front tire
can
get the "rear tire" treatment from the preceding wheel.
The front wheel set-up effect is especially true for "Michelin" wires,
the fine strands of stainless wire that make up steel belts of auto
tires. These wires, left on the road when such tires exposes
their
belt, cause hard to find slow leaks almost exclusively in rear tires.
When wet, glass can stick to the tire even in the flat orientation and
thereby get a second chance when it comes around again. To make
things worse, glass cuts far more easily when wet as those who have
cut rubber tubing in chemistry class may remember. A wet razor
blade
cuts latex rubber tubing in a single slice while a dry blade only
makes a nick.
As for pinch flats, aka snake bites, they occur on the rear wheel more
readily because it carries more load and is uncushioned when the rider
is seated. The rider's arms, even when leaning heavily on the
front
wheel, cushion impact when striking a blunt obstacle.
------------------------------
Subject: 8.17 What holds the rim off the ground?
From: Jobst Brandt <jbrandt@hpl.hp.com>
> What forces keep the rim of a wheel with pneumatic tires off the
> ground. It obviously can't be the air pressure because that's acting
> from top as well as from below.
As has been pointed out, the casing walls pull on the rim (or its
equivalent) and thereby support the load. The casing leaves the
rim
at about a 45 degree angle, and being essentially a circular cross
section, it is in contact with the rim over its inner quarter circle.
At least this is a good representative model. The visualization
may
be simpler if a tubular tire is considered. It makes no difference
whether the tire is held on by glue or is otherwise attaches to the
rim such as a clincher is. Either way the tire is attached to
the
rim, a relatively rigid structure.
Under load, in the ground contact zone, the tire bulges so that two
effects reduce the downward pull (increase the net upward force) of
the casing. First, the most obvious one is that the casing pulls
more
to the sides than downward (than it did in its unloaded condition);
the second is that the side wall tension is reduced. The reduction
arises from the relationship that unit casing tension is equivalent
to
inflation pressure times the radius of curvature divided by pi.
As
the curvature reduces when the tire bulges out, the casing tension
decreases correspondingly. The inflated tire supports the rim
primarily by these two effects.
Tire pressure changes imperceptibly when the tire is loaded because
the volume does not change appreciably. Besides, the volume change
is
insignificant in small in comparison to the volume change the air has
undergone when being compressed into the tire. In that respect,
it
takes several strokes of a frame pump to increase the pressure of a
tire from 100 psi to 101. The air has a low spring constant that
acts
like a long soft spring that has been preloaded over a long stroke.
Small deflections do not change its force materially. For convenience
car and truck tires are regularly inflated to their proper pressure
before being mounted on the vehicle.
------------------------------
Subject: 8.18 Anodized vs. Non-anodized Rims
From: Jobst Brandt <jbrandt@hpl.hp.com>
Date: Mon, 20 Apr 1998 15:31:32 PDT
Dark anodized rims were introduced a few years ago as a fashionable
alternative to shiny metal finish, possibly as a response to non
metallic composites. Some of these rims were touted as HARD anodized
implying greater strength. Hard anodizing of aluminum, in contrast
to
cosmetic anodizing, produces a porous ceramic oxide that forms in the
surface of the metal, as much as 1/1000 inch thick, about half below
the original surface and half above. It is not thick enough to
affect
the strength of the rim but because it is so rigid, acts like a thin
coat of paint on a rubber band. The paint will crack as the rubber
stretches before any load is carried by the rubber. Similarly,
anodizing cracks before the aluminum carries any significant load.
Rims are made from long straight extrusions that are rolled into
helical hoops from which they are cut to length. Rims are often
drilled and anodized before being rolled into a hoop and therefore,
the anodizing is already crazed when the rim is made. Micro-cracks
in
thick (hard) anodizing can propagate into the metal as a wheel is
loaded with every revolution to cause whole sections of the rim to
break out at its spoke sockets. In some rims, whole sidewalls
have
separated through the hollow chamber so that the spokes remained
attached to the inner hoop and the tire on the outer one. In
contrast, colored anodizing is generally too thin to initiate cracks.
As an example, Mavic MA-2 rims have rarely cracked except on tandems,
while the identical MA-40 rims, with a relativley thin anodizing, have
cracked often.
Anodizing is also a thermal and electrical insulator. Because
heat is
generated in the brake pads and not the rim, braking energy must flow
into the rim to be dissipated to the atmosphere. Anodizing, although
relatively thin, impedes this heat transfer and reduces braking
efficiency by raising the surface temperature of the brakes.
When
braking in wet conditions, road grit wears off anodizing on the
sidewall, an effect that improves braking.
Anodizing is not heat treatment and has no effect on the structural
properties of the aluminum.
------------------------------
Subject: 8.19 Reusing Spokes
From: Jobst Brandt <jbrandt@hpl.hp.com>
>I just bent my wheel and am probably going to need a new one
>built. Can I reuse my old, 3 months, spokes in the new wheel.
>The guy at the shop gave me some mumbo jumbo about tensioning or
>something.
There is no reason why you should not reuse the spokes of your
relatively new wheel. The reason a bike shop would not choose
to do
this is that they do not know the history of your spokes and do not
want to risk their work on unknown materials. If you are satisfied
that the spokes are good quality you should definitely use them for
you new wheel. The spokes should, however, not be removed from
the
hub because they have all taken a set peculiar to their location, be
that inside or outside spokes. The elbows of outside spokes,
for
instance, have an acute angle while the inside spokes are obtuse.
There are a few restrictions to this method, such as that new rim
must have the same effective diameter as the old, or the spokes will
be the wrong length. The rim should also be the same "handedness"
so that the rim holes are offset in the correct direction. This
is
not a fatal problem because you can advance the rim one hole so that
there is a match. The only problem is that the stem will not
fall
between parallel spokes as it should for pumping convenience.
Take a cotton swab and dab a little oil in each spoke socket of the
new rim before you begin. Hold the rims side by side so that
the
stem holes are aligned and note whether the rim holes are staggered
in the same way. If not line the rim up so they are. Then
unscrew
one spoke at a time, put a wipe of oil on the threads and engage it
in the new rim. When they are all in the new rim you proceed
as you
would truing any wheel. Details of this are in a good book on
building wheels.
The reason you can reuse spokes is that their failure mode is
fatigue. There is no other way of causing a fatigue failure than
to
ride many thousand miles (if your wheel is properly built). A
crash
does not induce fatigue nor does it even raise tension in spokes
unless you get a pedal between them. Unless a spoke has a kink
that
cannot be straightened by hand, they can all be reused.
------------------------------
Subject: 8.20 Clinchers vs. Tubulars
From: F.J. Brown <F.Brown@massey.ac.nz>
D.H.Davis@gdt.bath.ac.uk gave some useful hints on mounting clinchers,
mostly involving the use of copious quantities of baby powder, and
trying to convince me that clinchers aren't difficult to mount, so
ease of
mounting isn't a valid reason for preferring tubulars.
wernerj@lafcol.lafayette.edu wrote that although average tubulars ride
'nicer' than average clinchers, there are some clinchers around that
ride
just as 'nice'. He also said that ease of change isn't
a good reason for
preferring tubulars as if you flat in a race, you're either going to
swap
a wheel or drop out. He pointed out that tubulars end up
costing $20 -
$80 per flat.
ershc@cunyvm.cuny.edu gave some of the historic reasons that tubulars
were
preferred: higher pressures, lower weight, stronger, lighter rims.
Said
that only a few of these still hold true (rim strength/weight, total
weight),
but he still prefers the 'feel' of tubulars.
leka@uhifa.ifa.hawaii.edu started this thread with his observations
on
clinchers seperated from their rims in the aftermath of a race crash.
stek@alcvax.pfc.mit.edu comments on improperly-glued tubulars posing
a threat
to other racers by rolling off, and noted that this couldn't happen
with
clinchers.
jbrandt@hpl.hp.com agreed with stek, with the additional note that
it is inadequate inflation that often allows tubulars to roll.
Kevin at Buffalo agreed with stek and jobst about tubulars (improperly
or
freshly glued) sometimes rolling.
ruhtra@turing.toronto.edu says he uses clinchers for cost and convenience.
Clinchers let him carry around a tiny patch kit and some tyre irons,
costing
60c, whereas tubulars would require him to carry a whole tyre, and
would
cost more.
CONCLUSIONS: THE CLINCHER VS. TUBULAR WAR
Tubulars - used to be capable of taking higher pressures, had lower
weight
and mounted
onto stronger, lighter rims than clinchers. Clinchers
have now
largely caught up, but many cyclists thinking hasn't.
Tubular
tyre + rim combination still lighter and stronger.
- are easier to change
than clinchers. This matters more to some
people
than others - triathletes, mechanical morons and those
riding
in unsupported races.
- cost megabucks if
you replace them every time you puncture.
***However***
(and none of the North Americans mentioned this)
down here
in Kiwiland, we ***always*** repair our punctured
tubulars
(unless the casing is cut to ribbons). The process
doesn't
take much imagination, you just unstitch the case, repair
the tube
in the normal manner using the thinnest patches you can
buy, stitch
it back up again and (the secret to success) put a
drop of
Superglue over the hole in the tread.
- can roll off if
improperly glued or inflated. In this case, you
probably
deserve what you get. Unfortunately, the riders behind
you don't.
Clinchers - can be difficult to change (for mechanical morons) and are
always
slower to change than tubulars. Most people still carry a spare
tube and do their repairs when they get home.
- are cheaper
to run: if you puncture a lot clinchers will probably
still save you money over tubulars, even if you repair your
tubulars whenever possible. Tubulars are only repairable most
of the time, you virtually never write off a clincher casing due
to a puncture.
- have improved
immensely in recent years; top models now inflate
to high pressures, and are lighter and stronger than they used
to be. Likewise clincher rims. Some debate over
whether
tubulars are still lighter and tubular rims stronger. Probably
depends on quality you select. No doubt that high quality
clinchers/rims stronger, lighter and mor dependable than cheap
tubular/rim combination.
------------------------------
Subject: 8.21 Presta Valve Nuts
From: Jobst Brandt <jbrandt@hpl.hp.com>
Date: Fri, 07 Nov 1997 16:46:59 PST
Jam nuts on Presta valve stems and pumping.
1. The jam nut holds the stem when pumping so that it does not recede
into the rim when pressing the pump head against the tire.
This is
especially useful when the tire is flat (after installing
the
tube). It also keeps the stem from wiggling around
while pumping.
Removing the nut should present no difficulty unless the
threads
have been damaged or the hands are cold. The cold
may present a
problem, but then just opening the valve nut on a Presta
valve
under such conditions is difficult.
2. Breaking off stems with a frame pump comes from incorrect pumping.
The number of new tubes with broken stems lying along
the road
proves that this occurs far too often. To avoid
breaking the stem,
the pump head should be be held in the fist so that the
pumping
force goes from one hand into the other, not from the
pump into the
valve stem. To practice the correct action, hold
the pump head in
one hand with the thumb over the outlet, and pump vigorously
letting out no air. All the force goes from one
hand into the
other. This is essentially what should take place
when inflating a
tire.
It does no good to "get even" with the stupid tube by discarding
it
on the road for all to see. Most riders understand
how to pump a
tire and see this only as evidence of incompetence rather
than a
faulty tube. Besides, this ostentatious behavior
constitutes
littering for which the the fine in California is $1000.
Bike
shops should instruct new bike owners about the use of
the frame
pump. Along with this there should be some tire
patch hints like
don't try to ride a freshly patched tube, carry a spare
tube and
always use the spare after patching the punctured tube.
Of course
this is a whole subject in itself that is also treated
in the FAQ.
------------------------------
Subject: 8.22 Ideal Tire Sizes
From: Jobst Brandt <jbrandt@hpl.hp.com>
> I'm getting a custom frame built and wondered what
> people thought of using 26 inch road wheels. Smaller
> wheels ought to be lighter and stronger.
and goes on to list advantages and disadvantages, most of which are
less
that important in deciding what size to use. What in fact brought
us
the wheel size (700 or 27") that we have is better understood by the
women riders who have a hard time fitting these wheels into their small
bicycle frames. Wheels would be larger than they are if they
would fit
the average riders bike, but they don't. So the compromise size
is what
we are riding today.
> It seems to me that the most obvious reason for using 27"
> wheels is tradition, but I'm not sure the advantages make
> it worth trying to swim upstream. What do you think?
This line of thought is consistent with the "cost be damned" approach
in bicycling today. The big bucks are spent by people who want
the best
or even better than their peers. The more special the better.
Riders
consistently spend nearly twice the money for wheels and get worse
rims
when they choose anodized ones, whether there is merit to this finish
is of no interest. They cost more so they must be better.
How "custom"
can you get than to have wheels no one else on the block has (maybe
25"?).
If enough riders ask for 24", 25" and 26" wheels, manufacturers will
up
the price as their product lines multiply and the total sales remain
constant. Tires and spokes will follow as a whole range of sizes
that
were not previously stocked become part of the inventory. Meanwhile,
bike frames will come in different configurations to take advantage
of
the special wheel sizes. SIzes whose advantages are imperceptibly
small
but are touted by riders who talk of seconds saved in their last club
TT
or while riding to work.
A larger wheel rides better on average roads and always corners better
because it brings a longer contact patch to the road. A longer
contact
averages traction over more pavement and avoids slip outs for lack
of
local traction. Visualize crossing a one inch wide glossy paint
stripe
with a 27" wheel and an 18" wheel when banked over in a wet turn.
I see this subject arise now and then and it reminds me of the concept
of
splitting wreck.bike into several newsgroups. The perpetrators
bring the
matter up for many of the wrong reasons.
Ride bike, don't re-invent what has been discarded.
------------------------------
Subject: 8.23 Indexed Steering
From: Jobst Brandt <jbrandt@hpl.hp.com>
> In the several years I spent working in a pro shop, I have never
> seen a case of "index steering" (yes, we called it that) that was
> _not_ caused by a "brinelled" headset - one with divots in the
> races. I am 99.999 percent certain that that is your problem.
What
> are you going to do if you don't fix it? I suggest that you
fix the
> headset even if you sell the bike, as a damaged headset could be
> grounds for a lawsuit if the buyer crashes.
I disagree on two points. First, because you use the term "Brinell"
that conveys a notion as incorrect as the phrase "my chain stretched
from climbing steep hills" and second, because there is no possibility
of injury or damage from "indexed" steering head bearings.
Damage to head bearings seems to be twofold in this case because
properly adjusted steering, can only get looser from dimples and it
cannot be immobilized by them. Therefore, the head adjustment
was too
tight. However, dimpling is not caused by impact, but rather
by
lubrication failure that occurs while riding straight ahead.
This
occurs more easily with a correctly adjusted bearing than with a loose
one that rattles and clunks. Rattling replenishes lubricant between
balls and races that would otherwise not be present. Off road
bicycles suffer less from this malady than road bicycles because it
occurs primarily on long straight descents where no steering motions
that would replenish lubrication occur.
If you believe it comes from hammering the balls into the races, I
suggest you try to cause some dimples by hammering on the underside
of
the fork crown of a clunker bike of your choice. Those who hammered
cotters on steel cranks will recall no such dimpling on the spindle,
even though it has a far smaller diameter than the head bearing
although the blows were more severe and direct. No dimples were
made.
Ball bearings make metal-to-metal contact only under fretting loads
(microscopic oscillations) while the bearing is not turning.
Any
perceptible steering motion will replenish lubricant from the oily
meniscus surrounding the contact patch. Peering over the bars
at the
front hub while coasting down a road at 20+ mph you will notice the
fork ends vibrating fore and aft. This motion does not arise
at the
fork end, but at the fork crown, as it bends the steer tube.
Both
head bearings rotate in fretting motion crosswise to the normal plane
of rotation, as the steer tube bends. Dimples form in the forward
and
rearward quadrant of both upper and lower bearings from this fretting.
That they also form in the upper bearing shows they are not directly
load related.
Lubrication failure from fretting causes metal to metal contact to
form microscopic welds between balls and races. These welds
repeatedly tear material from the softer of the two causing the
elliptical milky dimples in the races. Were these brinelling
marks
(embossed through force), they would be shiny and smooth. Various
testimonials for the durability of one bearing over another are more
likely caused by the lubricant than the design of the bearing.
The
rigidly mounted ball bearing has survived longer as a head bearing
than it should, considering its poor performance record.
Roller bearings of various designs have been tried, and it appears
that they were the ones that finally made obvious that fore and aft
motion was the culprit all along; a motion that roller bearings were
even poorer at absorbing than balls. This recognition lead to
putting
spherical seats under the rollers. Although this stopped most
of the
dimpling, these bearings did not work well because the cage of needles
tended to shift off center and drag on the housing while the conical
races also shifted causing the bearing to bind.
It appears that a solution was finally found when Shimano bought a
patent from Wilderness Trail Bikes for a ball bearing that combined
the cup and cone ball bearing with the spherical plain bearing.
Today Shimano offers these bearings model called: LX, XT, 600, STX-RC
and Dura Ace. They have a full-complement angular-contact ball
bearing, whose races are sufficiently reentrant to snap permanently
together. They have rubber seals that retain grease for life
of the
bearing that is not exposed to weather. The ball bearing is supported
on a spherical steel ring that forms a plain bearing against the
aluminum housing. The plain bearing takes up the otherwise damaging
out-of-plane motion while the ball bearing does the steering.
The
bearing is only durable as long as the plain bearing remains properly
greased.
------------------------------
Subject: 8.24 Sidepull, Dual Pivot, and the Delta Brakes
From: Jobst Brandt <jbrandt@hpl.hp.com>
Date: Wed, 30 Oct 1996 15:03:28 PST
The bicycle brake has seen many variations since the introduction of
the standard single pivot caliper brake about 100 years ago.
This
brake, commonly called the side pull, has been the mainstay until a
wave of designs began about 30 years ago. Meanwhile the cantilever
brake with large wheel clearance existed only in a limited way until
the advent of the mountain bike. The need for wide clearance
over
large tires favors this brake that pivots from cantilevers on the fork
blades and does not restrict tire clearance. As is often the
case,
these advantages are not gained without drawbacks such as fork braking
forces that spread abd jam suspension forks unless a U-shaped stress
plate is used, and the steep angle of motion that causes the pads to
slip under the rim (total brake failure) with pad wear.
Until recently, most brakes had a hand lever ratio (mechanical
advantage) of 4:1, and a caliper or brake arm linkage with a 1:1
ratio, making most brakes and levers interchangeable. From time
to
time, brakes have been designed to address certain real or perceived
failings of the common caliper rim brake. Most of these had a
novel
linkage that promised a theoretical advantage. One of these,
the
centerpull brake of the 1950's, was the rave for nearly a decade, in
spite of being entirely without merit, being worse in all respects
than the side pull brake with which it competed. Its brief popularity
might indicate a dissatisfaction with the status quo.
Servo brakes, that use brake reaction force to reinforce application
force, have been designed without success. These schemes fail
for the
reason that a small change in the friction coefficient causes a large
change in braking, making control difficult. With self servo,
the
relationship between application force and brake response is non
linear and unpredictable. To escape this self servo effect in
drum
brakes, automobiles and motorcycles switched to disk brakes, where
the
brake application pressure is at right angles to the braking force.
It is curious that bicycles should try to switch the other way.
For lack of a power source such as cars have, other mechanisms with
variable ratios have been designed for bicycles, one of which was
recently turned into a major blunder for Campagnolo. Campagnolo
introduced the Delta brake (aka Modolo Chronos), whose mechanism is
an
equilateral parallelogram with the cable drawing two opposite corners
of a "diamond" together such that the other two corners expand.
The
motion can be visualized by placing the tips of the thumbs and
forefingers together to form a diamond, palms nearly together.
Moving
the tips of the diamond together at a constant rate demonstrates the
progressive nature of the mechanism and the resulting braking action,
the brake pads being connected by links to the knuckle joints as it
were.
The motion is a tangent function that goes from zero to infinity.
An
example of this is the motion of the top of a ladder, leaning steeply
against a wall, as the foot of the ladder moves away from the wall
at
a constant rate. At first the the top of the ladder moves
imperceptibly, gradually accelerating, until near the bottom its speed
approaches infinity. Although the Delta does not use the extremes
of
this range, it has this characteristic in contrast to a sidepull brake
that has a constant ratio throughout its range.
Although the sidepull brake remains the best performing brake to date,
its major flaw is that the return springs of the single pivot version
make sliding contact with the caliper arms. Because the contact
points are exposed, their friction is uncontrollable and invariably
lead to unequal retraction of the pads so that the brake is usually
off center and tends to drag. To avoid this, the single pivot
sidepull brake requires large pad-to-rim clearance that in turn
prescribes a low overall mechanical advantage of about 4:1 to
accommodate the reach of the human hand.
To offer greater leverage at the same total hand stroke, pad-to-rim
clearance must be reduced, which is only possible if pad position can
be guaranteed. The dual pivot brake achieves this with two pivot
points that define the line of action with two interlinked arms that
are constrained to move equally to remain centered. Precise centering
permits adjusting the pads as close to the rim as wheel trueness
permits. Typically, with minimal free travel, mechanical advantages
of about 5.6:1 are practical.
The higher leverage is not achieved entirely without compromise.
The
offset arm (the one on the right) sweeps its pad upward into the tire
so that this pad must be re adjusted as it wears. The brake cannot
track a crooked wheel that, for instance has a broken spoke.
Because
it has a high ratio, it does not work at all when the quick release
is
accidentally left open, and it changes its hand lever position about
40% faster with pad wear than a single pivot brake.
Part of the light feel of the dual pivot brake arises from the lower
(reverse) ratio of the caliper, whose springs now no longer exert as
strong a return force on the cable and hand lever. Because this
force
is lower, a return spring has been added to the hand lever. The
lower
cable return force coincidentally reduces cable drag during free
motion of the brake (before making contact with the rim). This
makes
the brake feel even more forceful because it has such a light action.
Hydraulic brakes have their own problems that keep them in an almost
invisible presence in general bicycling. Their advocates insist
that
they are superior in all respects in spite of their lack of acceptance
by the bicycling public at large.
------------------------------
Subject: 8.25 Seat adjustments
From: Roger Marquis <marquis@roble.com>
[More up to date copies of Roger's articles can be found at
http://www.roble.com/marquis/]
The following method of setting saddle height
is not the
only method around for setting your saddle height but it is the
most popular among coaches and riders both here and in Europe.
A) Adjust saddle level or very slightly nose
up, no more
than 2mm at the nose.
B) Put on the shoes you normally ride in. Have
wrench ready
(usually a 5mm Allen).
C) Mount the bike and sit comfortably, leaning
against a
wall. Hold a brake on with
one hand (or mount the bike on a
turbo trainer if you have
one).
D) Place your HEELS on the pedals, opposite
the clip, pedal
backwards at 30+ rpm without
rocking your pelvis (very
important).
E) Adjust seat height so that there is about:
E1) ZERO TO ONE HALF CM. for recreational riders (-50 mi/wk.),
E2) ONE HALF TO ONE CM. for experienced riders (50+ mi./wk.),
E3) ONE TO ONE AND ONE HALF CM. for endurance
cyclists (250+
mi./wk.), between
your heel and the pedal. If your soles are
thicker at the cleat
than at the heel adjust accordingly.
Don't forget to grease the seat post.
F) Ride. It may take a couple of rides to get
used to the
feel and possibly stretch
the hamstrings and Achilles
slightly.
Roger Marquis (marquis@roble.com)
------------------------------
Subject: 8.26 Cleat adjustments
From: Roger Marquis <marquis@roble.com>
[note: You may also want to consider going to a bike shop that
does
Fit Kit and have them do the Fit Kit RAD to adjust your cleats.
Many
people recommend it.]
[More up to date copies of Roger's articles can be found at
http://www.roble.com/marquis/]
A) Grease the cleat bolts and lightly tighten.
B) Sitting on the bike, put your feet in the pedals and adjust until:
B1) The ball of your foot is directly
above or, more commonly,
slightly
behind the pedal axle and:
B2) There is approximately 1 cm.
(1/2in.) between your ankle
and the
crank arm.
Note: Cleats that are adjusted too far
forward on the shoe can
cause excessive ankle movement and strain the Achilles
tendon.
C) Tighten the cleat bolts 80% and go out for
a ride. If another
position feels more comfortable
rotate your foot into that
position.
D) Carefully remove your shoes from the pedals
and tighten the
bolts fully. If you cannot
get out of the pedals without
shifting the cleats leave
your shoes on the bike and draw an
outline around the cleat.
Roger Marquis (marquis@roble.com)
------------------------------
Subject: 8.27 SIS Adjustment Procedure
From: Bob Fishell <spike@cbnewsd.att.com>
Shimano's instructions for adjusting SIS drivetrains varies from series
to series. The following method, however, works for each of mine
(600EX,
105, and Deore'). [Ed note: Works on Exage road and mtb
also.]
Your chain and cogs must be in good shape, and the cable must be free
of kinks, slips, and binds. The outer cable should have
a liner.
clean and lubricate all points where the cable contacts anything.
SIS adjustment:
1) Shift the chain onto the largest chainwheel and the smallest cog,
e.g., 52 and 13.
2) WITHOUT TURNING THE CRANKS, move the shift lever back until it
clicks, and LET GO. This is the trick to adjusting
SIS.
3) Turn the crank. If the chain does not move crisply onto the
next
inside cog, shift it back where you started, turn the
SIS barrel
adjuster (on the back of the rear derailleur) one-half
turn CCW,
and go back to step 2. Repeat for each pair of cogs
in turn
until you can downshift through the entire range of the
large
chainwheel gears without the chain hesitating. If
you have just
installed or reinstalled a shift cable, you may need to
do this
several times.
4) Move the chain to the small chainring (middle on a triple) and the
largest cog.
5) turn the cranks and upshift. If the chain does not move crisply
from the first to the second cog, turn the SIS barrel
adjuster
one-quarter turn CW.
If the drivetrain cannot be tuned to noiseless and trouble-free
SIS operation by this method, you may have worn cogs, worn chain,
or a worn, damaged, or obstructed shift cable. Replace as needed
and repeat the adjustment.
------------------------------
Subject: 8.28 Where to buy tools
You can buy tools from many sources. Some tools can be purchased
at
your local hardware store (wrenches, socket sets, etc), while the
special bike tools can be purchased from your local bike store or
one of the mail order stores listed elsewhere.
You can buy every tool you think looks useful, or just buy the tools
you need for a particular repair job. Buying the tools as you
need
them will let you build up a nice tool set over time without having
to drop a lot of money at once.
Some common tools you will need are:
Metric/SAE wrenches for nuts and bolts (or an assortment of adjustable
wrenches).
Screwdrivers, both flat and phillips.
Metric allen wrenches.
Pliers.
Wood or rubber mallet for loosening bolts.
Special tools and their uses:
Cone wrenches to adjust the hub cones.
Chain tool to take the chain apart for cleaning and lubrication,
and
to put it back together.
Tire irons for removing tires.
Spoke wrenches for adjusting spokes.
Cable cutters for cutting cables (don't use diagonal pliers!).
Crankarm tools for removing crankarms.
Bottom bracket tools for adjusting bottom brackets.
Headset wrenches to adjust the large headset nut.
------------------------------
Subject: 8.29 Workstands
There are a variety of workstands available, from about $30 to over
$130. Look at the mail order catalogs for photos showing the
different
types. The type with a clamp that holds one of the tubes on the
bike
are the nicest and easy to use. Park has a couple of models,
and their
clamp is the lever type (pull the lever to lock the clamp). Blackburn
and Performance have the screw type clamp (screw the clamp shut on
the
tube.
If you have a low budget, you can use two pieces of rope hanging from
the ceiling with rubber coated hooks on the end - just hang the bike
by the top tube. This is not as steady as a workstand, but will
do
an adequate job.
------------------------------
Subject: 8.30 Workstands 2
From: Douglas B. Meade <meade@bigcheese.math.scarolina.edu>
>>>>>>>>>> BICYCLE REPAIR STAND SUMMARY <<<<<<<<<<
The Park PRS6 was recommended by several (>5) responders; all
other models were recommended by no more than one responder.
Park PRS6
PROS: full 360\degree rotation
spring-loaded clamp is adjustable
very stable
CONS: not height adjustable
not easy to transport
clamp probably can't work with fat-tubed mtn bike
COST: ~$150
SOURCE: catalogs, local bike shops
Park Consumer
PROS: foldable
convenient
portable
CONS: not as stable as PRS6
COST: ~$100
SOURCE: catalogs, local bike shops
Park BenchMount
PROS: stronger, and more stable, than many floor models
CONS: must have a workbench with room to mount the stand
COST: $???
SOURCE: ???
Blackburn
PROS: The stand folds flat and is portable.
It has a 360 degree rotating clamp.
It is relatively stable.
CONS: crank-down clamp does not seem to be durable
crank bolt is not standard size; difficult to replace
hard to get clamp tight enough for stable use
clamp scratchs paint/finish
problems getting rotating mechanism to work properly
COST: ~$100
SOURCE: catalogs, local bike shops
Performance
PROS:
CONS: not too stable
Ultimate Repair Stand
PROS: excellent quality
includes truing stand
includes carrying bag
CONS:
COST: ~$225
SOURCE: order through local bike shop
the U.S. address for Ultimate Support Systems is :
Ultimate Support Systems
2506 Zurich Dr.
P.O. Box 470
Fort Collins, CO. 80522-4700
Phone (303) 493-4488
I also received three homemade designs. The first is quite simple:
hang the bike from coated
screw hooks
(available in a hardware store for less that $5/pair)
The others are more sophisticated. Here are the descriptions provided
by the designers of the systems.
Dan Dixon <djd@hpfcla.fc.hp.com> describes a modification
of the Yakima Quickstand attachment into a freestanding workstand
I picked up the Yakama clamp
and my local Bike shop for
around $25. What you
get is the clamp and a long carraige
bolt with a big (5") wing
nut. This is meant to be attached
to their floor stand or
their roof racks. The roof rack
attachment is ~$60; expensive,
but great for road trips.
I, instead, bought a longer
carraige bolt, a piece of
3/4" threaded lead pipe,
two floor flanges, and some 2x4's.
(about $10 worth of stuff).
You say you want to attach it to a bench (which should be easy)
pipe
+- clamp |
wing nut
|
| |
V
| +--+ V
| |---------+ V
| | O
| | | |\_________/| |
| /
| | -O- |=| _________ |=| |==I
| | | |/
\| | | \
| |---------+
| | O
| |
/\ /\ | |<-2x4
| | | |
flanges--+---------+ | |
| |
Excuse the artwork, but it
might give you and Idea about
what I mean. You could just
nail the 2x4 to the bench or
something. I really like
the clamp because it is totally
adjustable for different
size tubes.
Eric Schweitzer <ERSHC@cunyvm.cuny.edu> prefers the following
set-up to the Park `Professional' stands that he also has.
My favorite 'stand', one
I used for many years, one that I
would use now if my choice
of stand were mine, is made very
cheaply from old seats and
bicycle chain. Two seats (preferably
cheap plastic shelled seats)
(oh...they must have one wire
bent around at the front
to form the seat rails...most seats
do) have the rails removed
and bent to form 'hooks'. The
'right' kind of hooks are
placed in a good spot on the ceiling
about 5 or 6 feet apart.
(really, a bit longer than the length
of a 'typical' bike from
hub to hub. If you do a lot of tandems
or LWB recombants, try longer
:) Form a loop in one end of the
chain by passing a thin
bolt through the opening between 'outer'
plates in two spots on the
chain. (of course, this forms a loop
in the chain, not the bolt).
The same is done at the other end
to form loops to hold the
seat rail/hooks. First, form the hooks
so they form a pair of Js,
about 2 inch 'hook's The hook for the
front of the bike is padded,
the one for the rear looped through
the chain, squeezed together
to a single hook, and padded.
To use, hook the rear hook
under the seat, or at the seat stays.
Hook the front with each
arm on oposite sides of the stem. Can
also hook to head tube (when
doing forks). Either hook can grab
a rim to hold a wheel in
place while tightening a quick release
skewer or axle bolt. There
is no restricted access to the left
side of the bike. I try
to get the BB of a 'typical' frame about
waist height.
In closing, here is a general statement that only makes my decision
more difficult:
My best advice is to consider
a workstand a long term durable good.
Spend the money for solid
construction. Good stands don't wear or
break, and will always be
good stands until the day you die, at
which point they will be
good stands for your children. Cheese will
always be cheese until it
breaks.
------------------------------
Subject: 8.31 Frame Stiffness
From: Bob Bundy <bobb@ico.isc.com>
As many of you rec.bicycles readers are aware, there have been occasional,
sometimes acrimonious, discussions about how some frames are so much
stiffer than others. Cannondale frames seem to take most of the
abuse.
The litany of complaints about some bike frames is long and includes
excessive wheel hop, numb hands, unpleasant ride, broken spokes,
pitted headsets, etc. I was complaining to a friend of mine about
how there
was so much ranting and raving but so little empirical data - to which
he replied, "Why don't you stop complaining and do the measurements
yourself?". To that, I emitted the fateful words, "Why not, after
all,
how hard can it be?". Following some consultation with Jobst
and a few
other friends, I ran the following tests:
The following data were collected by measuring the vertical deflection
at
the seat (ST), bottom bracket (BB) and head tube (HT) as a result of
applying 80lb of vertical force. The relative contributions of
the
tires, wheels, fork, and frame (the diamond portion) were measured
using
a set of jigs and a dial indicator which was read to the nearest .001
inch. For some of the measures, I applied pressures from 20 to
270 lbs
to check for any significant nonlinearity. None was observed.
The same
set of tires (Continentals) and wheels were used for all measurements.
Note that these were measures of in-plane stiffness, which should be
related to ride comfort, and not tortional stiffness which is something
else entirely.
Bikes:
TA - 1987 Trek Aluminum 1200, this model has a Vitus front fork, most
reviews describe this as being an exceptionally
smooth riding bike
SS - 1988 Specialized Sirus, steel CrMo frame, described by one review
as
being stiff, hard riding and responsive
DR - 1987 DeRosa, SP/SL tubing, classic Italian road bike
RM - 1988 Cannondale aluminum frame with a CrMo fork, some reviewers
could not tolerate the rough ride of
this bike
TA
SS
DR
RM
----------
---------- ----------
----------
ST
BB HT ST BB HT
ST BB HS ST BB HT
diamond 1 1 0
2 2 0 2
2 0 1 1
0
fork 3 11 45
3 9 36 4 13
55 3 10 40
wheels 2 2 2
2 2 2 2
2 2 2 2
2
tires 68 52 66
68 52 66 68 52 66
68 52 66
total 74 66 113
75 65 104 76 69 123
74 65 108
What is going on here? I read the bike mags and this net enough
to know
that people have strong impressions about the things that affect ride
comfort. For example, it is common to hear people talk about
rim types
(aero vs. non-aero), spoke size, butting and spoke patterns and how
they
affect ride. Yet the data presented here indicate, just a Jobst
predicted,
that any variation in these factors will essentially be undetectable
to
the rider. Similarly, one hears the same kind of talk about frames,
namely, that frame material X gives a better ride than frame material
Y, that
butted tubing gives a better ride that non-butted, etc. (I may
have even
made such statements myself at some time.) Yet, again, the data
suggest
that these differences are small and, perhaps, even undetectable.
I offer
two explanations for this variation between the data and subjective
reports
of ride quality.
Engineering:
These data are all static measurements and perhaps only applicable
at the
end of the frequency spectrum. Factors such as frequency response,
and
damping might be significant factors in rider comfort.
Psychology:
There is no doubt that these bikes all look very different, especially
the
Cannondale. They even sound different while riding over rough
roads. These factors, along with the impressions of friends and
reviews
in bike magazines may lead us to perceive differences where they, in
fact,
do not exist.
Being a psychologist, I am naturally inclined toward the psychological
explanation. I just can't see how the diamond part of the frame
contributes
in any significant way to the comfort of a bike. The damping
of the frame
should be irrelevant since it doesn't flex enough that there is any
motion to actually dampen. That the frame would become flexible
at
some important range of the frequency spectrum doesn't seem likely
either.
On the other hand, there is plenty of evidence that people are often
very
poor judges of their physical environment. They often see relationships
where they don't exist and mis-attribute other relationships.
For example,
peoples' judgement of ride quality in automobiles is more related to
the
sounds inside the automobile than the ride itself. The only way
to get
a good correlation between accelerometers attached to the car seat
and
the rider's estimates of ride quality is to blindfold and deafen the
rider (not permanently!). This is only one of many examples of
mis-
attribution. The role of expectation is even more powerful.
(Some even
claim that whole areas of medicine are built around it - but that is
another story entirely.) People hear that Cannondales are
stiff and,
let's face it, they certainly *look* stiff. Add to that the fact
that
Cannondales sound different while going over rough roads and perhaps
the rider has an auditory confirmation of what is already believed
to
be true.
Unless anyone can come up with a better explanation, I will remain
convinced that differences in ride quality among frames are more a
matter of perception than of actual physical differences.
------------------------------
Subject: 8.32 Frame materials
[Ed note: I got this information from some of the books I have.
People
in the know are welcome to update this.]
There are several materials that are used to make bicycle frames.
They
are:
Mild steel - usually used in cheap department store bikes.
Frames
made from mild steel are heavy.
High carbon steel - a higher quality material used in low end
bikes.
Reynolds 500 is an example.
Steel alloy - lighter and better riding than high-carbon frames.
Reynolds
501 and Tange Mangaloy are examples.
Chro-moly - also called chrome-molybdenum or manganese-molybdenum
steel.
One of the finest alloys for bike frames. Reynolds 531 and
Columbus SL and SP are some of the best known brands.
Carbon fiber - high tech stuff. Made from space-age materials,
frames
made of this are very light and strong. Some problems
have been seen in the connections between the tubes and
bottom bracket, etc.
Aluminum - Light frames, usually with larger diameter
tubes.
Cannondale is a well-known brand.
------------------------------
Subject: 8.33 Bike pulls to one side
From: Jobst Brandt <jbrandt@hpl.hp.com>
For less than million dollar bikes this is easy to fix, whether it corrects
the cause or not. If a bike veers to one side when ridden no-hands,
it
can be corrected by bending the forks to the same side as you must
lean
to ride straight. This is done by bending the fork blades one
at a time,
about 3 mm. If more correction is needed, repeat the exercise.
The problem is usually in the forks although it is possible for frame
misalignment to cause this effect. The kind of frame alignment
error
that causes this is a head and seat tube not in the same plane.
This
is not easily measured other than by sighting or on a plane table.
The trouble with forks is that they are more difficult to measure even
though shops will not admit it. It takes good fixturing to align
a
fork because a short fork blade can escape detection by most
measurement methods. Meanwhile lateral and in-line corrections
may
seem to produce a straight fork that still pulls to one side.
However, the crude guy who uses the method I outlined above will make
the bike ride straight without measurement. The only problem
with
this is that the bike may pull to one side when braking because the
fork really isn't straight but is compensated for lateral balance.
This problem has mystified more bike shops because they did not recognize
the problem. Sequentially brazing or welding fork blades often
causes
unequal length blades and bike shops usually don't question this dimension.
However, in your case I assume the bike once rode straight so something
is crooked
------------------------------
Subject: 8.34 Frame repair
From: David Keppel <pardo@cs.washington.edu>
(Disclaimer: my opinions do creep in from time to time!)
When frames fail due to manufacturing defects they are usually
replaced under warranty. When they fail due to accident or abuse
(gee, I don't know *why* it broke when I rode off that last
motorcycle jump, it's never broken when I rode it off it before!)
you are left with a crippled or unridable bike.
There are various kinds of frame damage that can be repaired.
The
major issues are (a) figuring out whether it's repairable (b) who
can do it and (c) whether it's worth doing (sometimes repairs just
aren't worth it).
Kinds of repairs: Bent or cracked frame tubes, failed joints, bent
or missing braze-on brackets, bent derailleur hangars, bent or
broken brake mounts, bent forks, etc. A frame can also be bent
out
of alignment without any visible damage; try sighting from the back
wheel to the front, and if the front wheel hits the ground to one
side of the back wheel's plane (when the front wheel is pointing
straight ahead), then the frame is probably out of alignment.
* Can it be repaired?
Just about any damage to a steel frame can be repaired. Almost
any
damage to an aluminum or carbon fiber frame is impossible to repair.
Titanium frames can be repaired but only by the gods. Some frames
are composites of steel and other materials (e.g., the Raleigh
Technium). Sometimes damage to steel parts cannot be repaired
because repairs would affect the non-steel parts.
Owners of non-steel frames can take heart: non-steel frames can
resist some kinds of damage more effectively than steel frames, and
may thus be less likely to be damaged. Some frames come with
e.g.,
replacable derailleur hangers (whether you can *get* a replacement
is a different issue, though). Also, many non-steel frames have
steel forks and any part of a steel fork can be repaired.
Note: For metal frames, minor dents away from joints can generally
be ignored. Deep gouges, nicks, and cuts in any frame may lead
to
eventual failure. With steel, the failure is generally gradual.
With aluminum the failure is sometimes sudden.
Summary: if it is steel, yes it can be repaired. If it isn't steel,
no, it can't be repaired.
* Who can do it?
Bent derailleur hangers can be straightened. Indexed shifting
systems are far more sensitive to alignment than non-indexed.
Clamp
an adjustable wrench over the bent hanger and yield the hanger
gently. Leave the wheel bolted in place so that the derailleur
hanger
is bent and not the back of the dropout. Go slowly and try not
to
overshoot. The goal is to have the face of the hanger in-plane
with
the bike's plane of symmetry.
Just about any other repair requires the help of a shop that builds
frames since few other shops invest in frame tools. If you can
find
a shop that's been around for a while, though, they may also have
some frame tools.
* Is it worth it?
The price of the repair should be balanced with
* The value of the bicycle
* What happens if you don't do anything about the damage
* What would a new bike cost
* What would a new frame cost
* What would a used bike cost
* What would a used frame cost
* What is the personal attachment
If you are sentimentally attached to a frame, then almost any repair
is worth it. If you are not particularly attached to the frame,
then you should evaluate the condition of the components on the rest
of the bicycle. It may be cheaper to purchase a new or used frame
or even purchase a whole used bike and select the best components
from each. For example, my most recent reconstruction looked
like:
* Bike's estimated value: $300
* Do nothing about damage: unridable
* Cost of new bike: $400
* Cost of new frame: $250+
* Cost of used bike: $200+
* Cost of used frame: N/A
* Cost of repair: $100+
* Personal attachment: zip
Getting the bike on the road again was not a big deal: I have lots
of other bikes, but I *wanted* to have a commuter bike. Since
I
didn't *need* it, though, I could afford to wait a long time for
repairs. The cost of a new bike was more than I cared to spend.
It is hard to get a replacement frame for a low-cost bicycle.
I
did a good bit of shopping around and the lowest-cost new frame
that I could find was $250, save a low-quality frame in the
bargain basement that I didn't want. Used frames were basically
the
same story: people generally only sell frames when they are
high-quality frames. Because the bike was a road bike, I could
have
purchased a used bike fairly cheaply; had the bike been a fat-tire
bike, it would have been difficult to find a replacement. The
cost
of the frame repair included only a quick ``rattlecan'' spray, so
the result was aesthetically unappealing and also more fragile.
For
a commuter bike, though, aesthetics are secondary, so I went with
repair.
There is also a risk that the `fixed' frame will be damaged. I
had
a frame crack when it was straightened. I could have had the
tube
replaced, but at much greater expense. The shop had made a point
that the frame was damaged enough that it might crack during repair
and charged me 1/2. I was able to have the crack repaired and
I
still ride the bike, but could have been left both out the money
and without a ridable frame.
* Summary
Damaged steel frames can always be repaired, but if the damage is
severe, be sure to check your other options. If the bicycle isn't
steel, then it probably can't be repaired.
------------------------------
Subject: 8.35 Frame Fatigue
From: John Unger <junger@rsg1.er.usgs.gov>
I think that some of the confusion (and heat...) on this subject
arises because people misunderstand the term fatigue and equate it
with some sort of "work hardening" phenomena.
By definition, metal fatigue and subsequent fatique failure are
well-studied phenomena that occur when metal (steel, aluminum,
etc.) is subjected to repeated stresses within the _elastic_ range
of its deformation. Elastic deformation is defined as deformation
that results in no permanent change in shape after the stess is
removed. Example: your forks "flexing" as the bike rolls over a
cobblestone street.
(an aside... The big difference
between steel and aluminum
as a material for bicycles
or anything similar is that you
can design the tubes in
a steel frame so that they will
NEVER fail in fatigue. On
the other hand, no matter how
over-designed an aluminum
frame is, it always has some
threshold in fatigue cycles
beyond which it will fail.)
This constant flexing of a steel frame that occurs within the
elastic range of deformation must not be confused with the
permanent deformation that happens when the steel is stressed beyond
its elastic limit, (e. g., a bent fork). Repeated permanent
deformation to steel or to any other metal changes its strength
characteristics markedly (try the old "bend a paper clip back and
forth until it breaks" trick).
Because non-destructive bicycle riding almost always limits the
stresses on a frame to the elastic range of deformation, you don't
have to worry about a steel frame "wearing out" over time.
I'm sorry if all of this is old stuff to the majority of this
newsgroup's readers; I just joined a few months ago.
I can understand why Jobst might be weary about discussing this
subject; I can remember talking about it on rides with him 20 years
ago....
------------------------------
Subject: 8.36 Weight = Speed?
> I was wondering if anyone could help me figure out why heavier
> people roll down hills faster than the little scrawnies like myself.
Surface as well as cross sectional area of an object (a human body)
increases more slowly than its weight (volume). Therefore, wind
drag,
that is largely dependent on surface, is proportionally smaller for
a
heavier and larger object than a smaller one of similar shape and
composition. A good example is dust at a rock quarry that remains
suspended in the air for a long time while the larger pieces such as
sand, gravel, and rock fall increasingly faster to the ground.
They
are all the same material and have similar irregular shapes but have
different weight to surface area ratios, and therefore, different wind
resistance to weight ratios. This applies equally to bicyclists
coasting down hills if other factors such as clothing and position
on
the bicycle are similar.
------------------------------
Subject: 8.37 Adjusting SPD Cleats
Six adjustments can be made when setting up SPD cleats. With the
foot
parallel to the ground and pointing in the direction of travel, the
adjustments are:
1) Left/right translation
2) Front/back translation
3) Up/down translation
4) Front to back tilt
5) Side to side tilt
6) Azimuth, often called "rotation"
Front to back tilt is adjusted as the bicycle is pedaled since the
pedals themselves rotate freely in this direction.
Some people may need to adjust side to side tilt, but this requires
the use of shims which are not provided and can cause the cleat to
protrude beyond the tread of the shoe. Custom insoles that have
one side slightly thicker than the other may have the same effect
as shims between the cleat and the shoe.
Separate up/down adjustments for each leg may be necessary for
individuals with established leg length differences. To adjust
up/down translation in one shoe use a combination of an insole
and raise or lower the seat. To make small up/down changes
equally in both legs, simply raise or lower the seat.
The usual adjustments for SPD cleats are left/right, front/back,
and Azimuth. Of these Azimuth is the most sensitive. For
most
people these three adjustments are sufficient to obtain a
comfortable alignment.
-----------------
Aligning SPD cleats:
Position the cleat so that it lies on the imaginary line between the
bony knob on the inside of your foot at the base of your big toe and
a similar but smaller knob on the outside of the foot at the base of
the smallest toe. Set azimuth so that the pointed end of the
cleat
points directly toward the front of the shoe.
If you're switching from clips and straps, and you are satisfied with
your current alignment, use the following alternate method. Position
your SPD shoe fully in the clip of your old pedal and align the cleat
to the spindle of your old pedal. Center the cleat in the X direction,
leaving room to adjust either way should the need arise.
Some people find pedaling more comfortable if their left and right
feet are closer together. This is sometimes called the "Q-factor".
If you prefer to start with a low Q-factor, then move the cleat so
that
it is as close as possible to the outside of the shoe. Tighten
both
cleat bolts before engaging the pedal.
Adjust the release tension of the pedals so that it is somewhere in
the low to middle part of the tension adjustment range. The higher
the release tension, the harder it will be for you to disengage the
pedals when dismounting. The lower the release tension, the easier
it
will be for you to inadvertently pull out of the pedals, especially
when standing and pedaling. If you stand often to power up hills,
consider setting the initial release tension higher as an unwanted
release under these conditions can result in a painful spill.
See
the pedal instructions.
Mount your bike on a trainer, if you have one, to make preliminary
cleat and release tension adjustments. Practice engaging and
disengaging the pedals a few times before you take a real ride.
Soon you will find this easy. If you notice that a shoe rubs
a
crank or chainstay, adjust left/right translation and azimuth
until the shoe no longer rubs.
As you pedal, you will probably find the initial azimuth
uncomfortable on one or both legs. Notice how your foot would
like
to rotate. Adjust the azimuth of the appropriate cleat in the
same
direction your foot wants to rotate. For example, if your foot
wants to rotate clockwise, adjust the azimuth of the cleat (when
looking at the bottom of the shoe) clockwise. Start by making
moderate corrections. If you overshoot the adjustment, correct
by
half as much.
As you approach optimum azimuth, you may need to ride longer before
you notice discomfort. Take your bike off the trainer, and go
for
a real ride! And bring your 4mm allen key.
You may find very small azimuth adjustments difficult to make.
This
happens because the cleat has made an indentation in the stiff sole
material (usually plastic, sometimes with a tacky, glue-like
material where a portion of the sole was removed). When you tighten
the cleat after making a small correction, it will tend to slide back
into the old indentation. Try moving the cleat one millimeter
or so
to the side or to the front or back, so the cleat can no longer slip
into the old indentation pattern as it is being tightened.
Pain in the ball of your foot can be relieved. One way is by moving
the cleat rearward. Start by moving the cleat about two to three
millimeters closer to the rear of the shoe. Be careful not to
change
the azimuth. When pedaling notice how far your heel is from the
crank. After making a front/rear adjustment, check to make sure
the
crank-heel distance has not noticeably changed.
Moving a cleat rearward on the shoe has the effect of raising your seat
by a lesser amount for that leg. The exact expression is messy,
but
for an upright bike, the effect is similar to raising your seat by
about y/3 for that leg, where y is the distance you moved the cleat
to
the rear. For example, if you move your cleat 6 millimeters to
the
rear, you might also want to lower your seat by about 2 millimeters.
Remember, though, that unless both cleats are moved rearward the same
amount, your other leg may feel that the seat is too low.
Another way to relieve pain in the ball of the foot is to use a custom
orthotic and/or a padded insole. Most cycling shoes provide poor
arch
support and even poorer padding.
After riding for a while with your aligned cleats if you find yourself
pulling out of the pedals while pedaling, you will need to tighten
the
release tension. After tightening the release tension the centering
force of the pedals will be higher, and you may discover that the
azimuth isn't optimum. Adjust the azimuth as described above.
On the other hand, if you find you never pull out of the pedals while
pedaling and if you find it difficult or uncomfortable to disengage
the cleat, try loosening the release tension. People whose knees
like some rotational slop in the cleat may be comfortable with very
loose cleat retension.
As with any modification that affects your fit on the bike, get used
to your pedals gradually. Don't ride a century the day after
you
install SPDs. Give your body about two or three weeks of gradually
longer rides to adapt to the new feel and alignment, especially if
you've never ridden with clipless pedals before. Several months
after
installing SPDs, I occasionally tinker with the alignment.
After performing the above adjustments if you are still uncomfortable,
seek additional help. Some people can be helped by a FitKit.
If
you're lucky enough to have a good bike shop nearby, seek their
advice.
-----------------
Tightening cleat bolts:
Tighten cleat bolts until they _begin_ to bind. This will happen
when
further tightening produces a vibration or squeal from the cleat.
Tighten no further or you may damage the mounting plate on the inside
of the shoe. After living for a while with a comfortable
alignment,
remove each mounting bolt separately, apply blue loctite on the
threads, and reinstall. Should you later find you need to loosen
a
bolt to adjust the alignment, you will have to reapply the loctite.
Keeping the Pedal/Cleat interface clean:
Occasionally you may find the pedals suddenly more difficult to
disengage. This usually happens because dirt or other contaminants
get caught in the cleat or pedal mechanism. I have found that
a good
spray with a hose quickly and cleanly washes off dust, mud, or other
gunk from the pedal and cleat. You may also wish to spray the
pedal
with a light silicone or teflon lubricant.
Acknowledgements:
John Unruh (jdu@ihlpb.att.com)
Lawrence You (you@taligent.com)
-----------------
Case History:
I have sensitive legs--feet, ankles, knees, tendons, etc. If the
cleats aren't aligned properly, I feel it. I took a long time
to find
a cleat alignment that was comfortable for long and/or intense rides.
I ride a Bridgestone RB-T, 62cm frame, triple chainring. I wear
size
48 Specialized Ground Control shoes--evil-looking black and red
things. They were the only shoes I could find in my size that
were
comfortable. When I installed the M737 pedals, I had 175mm cranks.
I set the release tension so that the indicator was at the loose end
but so that I could see the entire nut in the slot.
The azimuth I found most comfortable had both shoes pointing roughly
straight ahead. The ball of my left foot began hurting, so I
moved
the left cleat back about 4-6mm. This placed the ball of my foot
in
front of the pedal spindle. I did not make any left/right
adjustments.
Unfortunately, on longer rides, the ball of my left foot still hurt,
so I got a pair of custom CycleVac "Superfeet" insoles. I removed
the
stock insole from the shoe, and inserted the CycleVac insole.
The
CycleVac doesn't have any padding at the ball, and my foot didn't like
the hard plastic sole of the shoe. I had a pair of thin green
Spenco
insoles lying around, so I put those under the CycleVacs to provide
some padding. I didn't use the stock insoles because they are
too
thick. Finally, the pain was gone! If I remain pain-free
for a while
I may try moving the left cleat forward again.
Then I replaced the 175mm cranks with 180mm cranks, and I lowered the
seat 2.5mm. My left foot was still happy, but my right knee began
to
complain. Not only that, but my right foot felt as if it was
being
twisted to the right (supinating), toward the outside of the pedal.
After fussing with the azimuth of the right cleat, I couldn't find
a
satisfactory position, though I could minimize the discomfort.
I moved the right cleat as far as I could to the outside of the shoe,
bringing my foot closer to the crank. I also reduced the release
tension further. The red indicating dots are now just visible.
This
helped my knee, but my foot still felt as if it were being twisted,
as if all the force were being transmitted through the outside of the
foot. In addition, my left Achilles Tendon started to hurt at
times.
I lowered the seat another couple millimeters. This helped, but
I
felt that my right leg wasn't extending far enough. Then I tried
_rotating_ the saddle just a little to the right, so the nose was
pointing to the right of center. This helped. But my right
foot
still felt supinated, and my right knee started to hurt again.
I removed the right CycleVac insole and Spenco insole and replaced them
with the original stock insole that provides little arch support.
Bingo. The discomfort was gone. It seems I need the arch
support for
the left foot but not for the right foot.
How long will it be before I make another tweak? The saga continues...
-----------------
Copyright 1993, Bill Bushnell. Feel free to distribute this article
however you see fit, but please leave the article and this notice
intact.
------------------------------
Subject: 8.38 Rim Tape Summary
From: Ron Larson <lars@craycos.com>
This is a summary of the experience of riders on the net regarding
various rim tapes, both commercial and improvized. Any additional
comments and inputs are welcome.
RIM TAPE
Rim tape or rim strips are the material that is placed inside a
clincher rim to protect the tube from sharp edges of the nipple holes
and possibly exposed ends of spokes extending beyond the nipples. Many
materials have been used to produce rim tapes: plastic, rubber, tapes
consisting of a multi-directional fiber weave, duct tape and fiberglass
packing tape.
A few factors influence how well a rim tape works. Some of the tapes
are available in more than one width. It is important to choose the
width that provides the best fit to cover the entire "floor" of the
rim
as opposed to a tape that is barely wide enough to cover the nipple
holes. Another factor is how well the rim tape withstands the stress
of
being stretched over the nipple holes with a high preassure inner tube
applying preassure to it. The main form of failure of the plastic tapes
is for the tape to split lengthwise (in the direction the tube lies
in
the rim) under high preassure forming a sharp edge that the tube
squeezes through and then rubs against. Thus the splitting tape causes
the flat that it was supposed to be protecting against.
REVIEW OF RIM TAPES BY TYPE
Plastic Tapes
Advantages:
Easy to install and remove. No sticky side is involved.
Disadvantages:
Although there are exceptions, they are prone to splitting under
preassure.
Michelin Good Experiences: 0 Bad Experiences: 6
Cool Tape Good Experiences: 2 Bad Experiences: 0
Cool Tape is thicker than other plastic tapes and does not exhibit
the splitting failure noted above.
Hutchinson Good Experiences: 0 Bad Experiences: 2
Specialized Good Experiences: 1 Bad Experiences: 4
Rubber Tapes
Advantages:
Easy to install and remove. Good if the nipples are even with the rim
floor and there are no exposed spoke ends.
Disadvantages:
Stretch too easily and allow exposed nipple ends to rub through the
tape and then through the tape.
Rubber strips Good Experiences: 0 Bad Experiences: 2
Cloth tapes woven of multi-directional fibers:
Advantages:
Easy to install. Do not fail under preassure.
Disadvantages:
They are a sticky tape and care must be taken not to pick up dirt if
they need to be removed and re-installed.
Velox Good Experiences:11 Bad Experiences: 0
Velox rim tape comes in three different widths. Be sure to get
the
widest tape that covers the floor of the rim without extending
up the
walls of the rim. The stem hole may need to be enlarged
to allow the
stem to seat properly. Otherwise the stem may push back into
the tube
under preassure and cause a puncture at the base of the stem.
Non-commercial rim tapes
Fiberglass packing tape (1 or 2 layers)
Advantages:
Cheap. Readily available. Easy to install.
Disadvantages:
Impossible to remove. If access to the nipples is required, the tape
must be split and then either removed and replaced or taped over.
Fiberglass packing tape Good Experiences: 1 Bad Experiences: 1
Duct tape (hey, someone tried it!!)
Advantages:
CHEAP. Readily available.
Disadvantages:
Useless. Becomes a gooey mess that is impossible to remove.
Duct tape Good Experiences: 0 Bad Experiences: 1
CONCLUSION
While plastic tapes are easy to work with, they often fail. The clear
winner in this survey is the Velox woven cloth tape. A quick review
of
mail order catalogs confirms the experiences of the net. Velox was
available in 5 out of 5 catalogs checked. It was the only rim
tape
available in 3 of the catalogs. The other 2 had one or two plastic
tapes available. (None sold duct tape...)
One good suggestion was a preassure rating for rim tapes much like the
preassure rating of tires.
------------------------------
Subject: 8.39 STI/Ergo Summary
From: Ron Larson <lars@craycos.com>
This is the second posting of the summary of STI/Ergo experience. The
summary was modified to include more on STI durability and also the
range of shifting avaliable from each system. As before, I am open
to
any comments or inputs.
lars
THE CASE FOR COMBINED SHIFTERS AND BRAKES.
Shifters that are easily accessible from either the brakehoods or the
"drop" position are an advantage when sprinting or climbing because
the
rider is not forced to commit to a single gear or loose power / cadence
by sitting down to reach the downtube shifters. They also make it much
easier to respond to an unexpected attack.
At first the tendency is to shift more than is necessary. This tendency
levels out with experience. There is also an early tendency to do most
shifting from the bakehoods and the actuators seem to be difficult
to
reach from the drop position. This discomfort goes away after a few
hundred miles of use (hey, how many times have I reached for the
downtube on my MTB or thumbshifters on my road bike???). All
experienced riders expressed pleasure with the ability to shift while
the hands were in any position, at a moments notice.
The disadvantages are extra weight, added weight on the handlebars
(feels strange at first) and expense. Lack of a friction mode was
listed as a disadvantage by a rider who had tried out STI on someone
elses bike but does not have Ergo or STI. It was not noted as a problem
by riders with extended Ergo / STI experience. A comparison of the
weight of Record/Ergo components and the weight of the Record
components they would replace reveals that the total weight difference
is in the 2 to 4 ounce range (quite a spread - I came up with 2 oz
from
various catalogs, Colorado Cyclist operator quoted 4 oz of the top
of
his head). The weight difference for STI seems to be in the same
range. The change probably seems to be more because weight is
shifted
from the downtube to the handlebars.
There was some concern from riders who had not used either system
regarding the placement of the actuating buttons and levers for Ergo
and STI and their affect on hand positions. Riders with experience
have
not had a problem with the placement of the actuators although one
rider stated that the STI brakehoods are more comfortable.
ADVANTAGES OF EACH SYSTEM.
The Sachs/Ergo system was mentioned as a separate system. In fact
(according to publications) it is manufactured By Campagnolo for Sachs
and is identical to the Campagnolo system with the exception of spacing
of the cogs on the freewheel/cassette. With the Ergo system,
all
cables can be routed under the handlebar tape while the STI system
does
not route the derailleur cables under the tape. Those that voiced
a
preference liked the clean look of the Ergo system.
Both Ergo and STI seem to be fairly durable when crashed. Experience
of riders who have crashed with either system is that the housings
may
be scratch and ground down but the system still works. The internal
mechanismsof both systems are well protected in a crash.
Both Ergo and STI allow a downshift of about 3 cogs at a time. This
capability is very handy for shifting to lower gears in a corner to
be
ready to attack as you come out of the corner or when caught by
surprise at a stop light. Ergo also allows a full upshift from the
largest to the smallest cog in a single motion while STI requires an
upshift of one cog at a time.
Riders voiced their satisfaction with both systems. While some would
push one system over the other, these opinions were equally split.
------------------------------
Subject: 8.40 Roller Head Bearings
From: Jobst Brandt <jbrandt@hpl.hp.com>
Roller head bearings provided an advantage that is not directly
connected with rollers. However, compound ball and plain bearings
have recently replaced rollers as is described in the item on "Indexed
Steering". The main advantage of rollers was that they have two
bearings in one that is important because the bearing must accomplish
two functions. The problem of the head bearing is so obscure,
that
until recently, no one had taken into account that head bearing is
subjected different motion than is apparent.
The bearing serves as a hinge about which the front wheel assembly
rotates, but it also absorbs another motion, and this is the problem.
As the bicycle rolls over roughness, the fork absorbs shock mostly
by
flex just above and below the fork crown that makes it rotate fore
and
aft about a horizontal axis. The motion can be seen by sighting
over
the handle bars to the front hub while rocking the bicycle fore and
aft with the front brake locked. This is what occurs when rolling
down a paved road but with much smaller amplitude.
The angles through which the fork crown swivels are extremely small
in
contrast to the relative motion at the hub because the distance
between the hub and the fork crown is large. This motion is not
in
itself damaging to the bearing because it is only a small misalignment
that cup and cone ball bearings absorb easily. The damage occurs
when
these small motions occur when there are no steering motions to
replenish lubricant while the bearing balls fret in place. Fretting
breaks down the lubricant film on which the balls normally roll and
without which they weld to the races and tear out tiny particles.
Because rollers could not absorb these motions, they were equipped
with spherical backing plates hat could move in that direction.
This
was the contribution rollers made before they were replaced by ball
bearings that had this same feature. Balls, in contrast to rollers,
stay in alignment and do not bind up from sliding off center as
rollers often did.
See item on "Indexed Steering".
------------------------------
Subject: 8.41 Tubular Tire Repair
From: Jobst Brandt <jbrandt@hpl.hp.com>
Date: Mon, 20 Apr 1998 15:31:32 PDT
Opening the Tire
The tire casing must be opened to gain access to patch the tube.
To
do this, open the casing by peeling the base tape back and unstitching
the seam. If this is a seamless tire, chuck it. There are
two types
of seams, zipper stitch (using one thread) and two thread stitch.
The
zipper stitch is identified by having only one thread. It appears
to
make a pattern of slanted arrows that point in the direction in which
it can be 'unzipped'.
Never open more tire than is necessary to pull the tube out of the
casing. Remember, the tube is elastic and can be pulled a long
way
from a three cm long opening. Even if there are two punctures
not too
far apart, the tube can be pulled out of a nearby opening. However,
to insert a boot requires an opening of about 6 to 10 cm at the
location of the cut or rupture, about the length of the boot (at least
10cm) and a couple of cm more.
Base Tape
Never cut the base tape because it cannot be butt joined. Always
pull
it to one side or separate it where it is overlapped. Do not
cut the
stitching, because it takes more time to pull out the cut thread than
to pull it out in one piece. When working on the stem, only unstitch
on one side of the stem, preferably the side where machine finished.
Use latex to glue down loose threads on a sidewall cut. Paint
the
exposed casing zone that is to be covered by the base tape and the
tape with latex emulsion, allow to partially dry and put the tape in
place. Put the tire on a rim and inflate hard.
Zipper Stitch
Cut the thread at some convenient place at the upstream end of the
intended opening and with a blunt awl, like a knitting needle, pull
out several stitches in the direction the stitch pattern points.
When
enough thread is free to pull on, the stitching can be opened like
a
zipper. When enough seam is open, thread the loose end through
the
last loop and pull tight, to lock the zipper. Don't cut off the
free
end because it is often good enough to re-sew the seam.
Two Thread Stitch
One of the threads makes a zig zag as it locks the other thread where
it penetrates the tire casing. Cut both threads near the middle
of
the opening and, with a blunt awl like a knitting needle, pull out
only the locking thread in both directions, stitch at a time.
The
locking thread is the one that is easier to pull out. Remove
as many
stitches as the opening requires. The other thread pulls out
like a
zipper. Tie a square knot with the loose ends at both ends of
the
opening and cut off the rest.
Patching
Patch butyl (black) tubes using patches from a bicycle patch kit.
To patch a latex tube, make patches from an old latex tube that are
fully rounded and just large enough to cover the hole plus five mm.
For instance, a thorn hole takes a 10 mm diameter patch. Use
Pastali
rim glue (tire patch glue also works but not as well) wiped thinly
onto the patch with your finger. Place the patch on the tube
immediately and press flat. Latex will pass the volatile solvent
allowing the glue to cure rapidly with good adhesion to the tube.
Casing Repair
Repairing tubular tires requires latex emulsion. You can get
it from
carpet layers, who usually have it in bulk. You must have a container
and beg for a serving. If you are repairing a tubular you probably
ride them, and therefore, will have dead ones lying around. The
best
tubulars generally furnish the best repair material.
Most cuts of more than a few cords, like a glass cut, require a
structural boot. With thin latex tubes, uncovered casing cuts
will
soon nibble through the tube and cause another flat. For boot
material, pull the tread off a silk sprint tire, unstitch it and cut
off the bead at the edge of the fold. Now you have a long ribbon
of
fine boot material. Cut off a 10cm long piece and trim it to
a width
that just fits inside the casing of the tire to be booted from inside
edge of the bead (the folded part) to the other edge.
The boot must be trimmed using a razor blade to a thin feathered edge
so that the tube is not exposed to a step at the boot's edge,
otherwise this will wear pinholes in a thin latex tube. Apply
latex
to the cleaner side of the boot and the area inside the tire,
preferably so the boot cords are 90 degrees from the facing tire
cords.
Insert the boot and press it into place, preferably in the natural
curve of the tire. This makes the the boot the principal structural
support when the tire is again inflated, after the boot cures.
If the
casing is flat when the boot is glued, it will stretch the casing more
than the boot upon inflation. After the boot dries, and this
goes
rapidly, sew the tire.
Tube Replacement
To replace the entire tube, open the tire on one side of the stem,
the
side that seems to be easier to re-sew after the repair. Open
about
eight to ten cm the usual way, so that the old tube can be pulled out
by the stem. Cut the tube and attach a strong cord to the loose
end
of the tube to be pulled through the casing as you pull the old tube
out.
Cut the "new" latex tube about 5 cm away from the stem, tie the cord
onto the loose end and pull it gently into the casing. Dumping
some
talc into the casing and putting talc onto the tube helps get the tube
into place. With the tube in place, pull enough of it out by
stretching it, to splice the ends together.
Splicing the Tube
This procedure works only with latex tubes. Overlap the tube
ends so
the free end goes about one cm inside the end with the stem.
With the
tube overlapped, use a toothpick to wipe Pastali rim cement into the
interface. The reason this MUST be done in place is that the
solvent
will curl the rubber into an unmanageable mess if you try this in free
space. Carefully glue the entire circumference and press the
joint
together by pressing the tube flat in opposing directions. Wait
a
minute and then gently inflate to check the results. More glue
can be
inserted if necessary if you do not wait too long.
Sewing the Tire
Sewing machines make holes through the bead that are straight across
at a regular stitch interval. For best results, you must use
the
original stitch holes when re-sewing. Use a strong thread (one
that
you cannot tear by hand) and a (triangular) needle from a Velox
tubular patch kit (yes I know they are scarce). Make the first
stitch
about one stitch behind the last remaining machine stitch and tie it
off with a noose knot.
With the beads of the tire pressed against each other so that the old
holes are exactly aligned, sew using a loop stitch pulling each stitch
tight, going forward two holes then back one, forward two, back one,
until the seam is closed. This is a balanced stitch that uses
one
thread and can stretch longitudinally.
Gluing Tire to Rim
For road tires, that are intended to be manually mounted and replaced
on the road, tires with a rubberized base tape are preferred because
these are easily and securely mounted by applying a coating of glue
to
the rim, allowing it to harden and mounting the tire to be inflated
hard so that it will sink in and set.
Because road tires are intended to be changes on the road, they use
a
glue that does not completely harden and allows reuse for mounting
a
spare.
Track tires, in contrast can be mounted using hardening glue such as
shellac or bicycle tire track glue. This glue is best suited
for base
tapes that are "dry" cloth. The tire is mounted either with a
light
coating of track glue on the base tape or un-glued onto a good base
of
track glue whose last coat is still soft on the rim, into which the
tire will set when inflated upon mounting. Hard glue prevents
rolling
resistance otherwise generated by the gummy road glue. Track
glue is
primarily useful for record attempts where every effort is needed.
Mounting a Tubular
The most effective and fastest way to mount a tubular is to place the
rim upright on the ground, stem hole up; insert the valve stem of the
tire and with both hands stretch the tire with downward force to
either side, working the hands downward to the bottom of the rim
without allowing the tire to slacken. Try this before applying
rim
glue on a dry rim and inflate the tire hard so that afterward,
mounting is easier on the glued rim.
Note that inflation pressure causes the tire to constrict until the
cord plies are at about 35 degrees. This effect helps retain
the tire
on the rim in use. Therefore, do not inflate a tire to mount
it.
Tubulars should generally not be inflated off a rim because this
deforms the tire and base tape adversely, possibly shearing the
inter-ply adhesion and loosening the base tape and stitching.
Now that you know everything there is to know about this, get some
practice. It works, I did it for years.
------------------------------
Subject: 8.42 Cassette or Freewheel Hubs
From: Jobst Brandt <jbrandt@hpl.hp.com>
All cassette hubs are not nearly alike. That is apparent from
the
outside by their appearance and by the sprockets that fit on them.
More important to their longevity is how their insides are designed.
Among the mainline brands, some are a response not only to the choice
and interchangeability of sprockets but to the problem of broken rear
axles and right rear dropouts. These failures are caused by bending
loads at the middle of the rear axle that arise from bearing support
that is not at the ends of the axle. The following diagrams attempt
to categorize the freewheel and hub combination, and two cassette
designs with respect to these loads.
|
H
H | |
H
H Io-- |
/-------------------\ -o\
O
O------
===X==================wX========= Axle
has weak spot at "w"
O
O------ (Freewheel
& hub)
\-------------------/ -o/
H
H Io-- |
H
H | |
|
|
H
H | |
H
H | | |
/------------------\ /----\
O
O O----O
===X==================XwX====X=== Axle
has weak spot at "w"
O
O O----O (Hugi and Campagnolo)
\------------------/ \----/
H
H | | |
H
H | |
|
|
H
H | |
H
H | | |
/------------------\/o---o\
O
\-----O
===X=========================X=== Axle
is loaded only at ends
O
/-----O (Shimano
and SunTour)
\------------------/\o---o/
H
H | | |
H
H | |
|
For clarity only three sprocket gear clusters are shown.
Strong cyclists put the greatest load on the axle by the pull of the
chain because there is a 2:1 or greater lever ratio from pedal to
chainwheel. The freewheel in the first diagram has the greatest
overhung load when in the rightmost sprocket. The second design
has
the greatest bending moment on the axle when in the leftmost sprocket
and the third design is independent (in the first order) of chain
position. This third design carries its loads on bearings at
the ends
of the axle for minimum axle stress while the other two put a large
bending moment on the middle of the axle.
Common freewheel hubs have not only the highest bending stress but the
smallest axle at 10mm diameter with threads that help initiate
cracking. The second design type generally uses a larger diameter
axle to avoid failure. However, these axles still have significant
flex that can adversely affect the dropout.
There are other important considerations in selecting a hub.
Among these are:
1. Durability of the escapement and its angular backlash (t/rev).
2. Flange spacing, offset, and diameter.
3. Type of bearings (cone / cartridge) and environmental immunity.
4. Ease of sprocket replacement and cost.
Currently the best solution for sprocket retention is a splined body
that allows individual sprockets to be slipped on and be secured by
an
independent retainer. Screwing sprockets onto the body is
indefensible, considering the difficulty of removal. The same
goes
for freewheels. No longer needing to unscrew tight freewheels
is
another advantage for cassette hubs.
------------------------------
Subject: 8.43 Cassette or Freewheel Hubs take 2
From: David Keppel <pardo@cs.washington.edu>
People often ask ``should I use a freewheel or a freehub?'' The
answer is usually ``yes.''
The hub is the center of a wheel and is composed of an axle, bolted
to
the bike frame, a hub shell or hub body, where the spokes attatch,
and
bearings to let the shell rotate around the axle.
Freewheels screw onto threads on the rear hub's shell, and cogs
attatch to the freewheel. The freewheel's job is to provide a
ratchet
between the cogs and the hub shell, so that you can coast. Freehubs
are similar but combine parts of the freewheel with parts of the hub
shell. Freehubs are also sometimes called ``cassettes''.
The usual problem with rear hubs is that axles bend and break.
This
is because the axle diameter was chosen when single cogs were used
and
the hub bearing was positioned close to the frame. Since then,
wider
cog clusters have become the norm, the bearings and frame have moved
further apart and leverage on the axle has increased. But since
the
axle has not gotten any stronger, it now has a tendency to fail.
Cassettes fix the problem by incorporating one hub bearing in to the
freewheel mechanism, so that the bearing is once again outboard and
the axle is carrying its load under less leverage. Some freewheel
hubs
solve the problem by using fatter axles. Since increasing the
axle
diameter dramatically improves axle strength, this is an effective
solution and it is possible to use a fat axle that is aluminum and
thus
lighter than a standard skinny (weaker) steel axle.
Neither solution is perfect -- cassette hubs let you use standard
replacement axles, cones, washers, etc., but force you to use cogs
and
spacers and whatnot by a particular manufacturer (and possibly
derailleurs and shifters -- e.g. XTR uses 4.9mm cog-to-cog spacing
instead of the normal 5.0mm). On the other hand, fat axles are
nonstandard as are some other replacement parts.
As an aside, the cassette solution leaves a fairly long unsupported
axle stub on the left side, and this is sometimes a source of more
bending problems. Fatter axles solve the problem on both sides.
Note also that many cassette systems allow you to remove the cogs using
a lightweight tool and thus give you ready access to the spokes in
case
of breakage. Freewheels attatch with a fine thread (another historical
artifact, I believe) and are thus more difficult to remove on the road,
making spoke replacement harder.
In principle, freehubs have all cogs attatch using the same size and
shape of spline, so, e.g., a 20T cog can be used as both a large cog
for a corncob cluster and as a middle cog for wide-range cluster.
However, Shimano's marketing is just the opposite and is directed at
selling whole clusters, without letting you replace individual cogs.
(Shimano's policy is relevant here since they sell 90+% of such hubs.)
Freewheels have several spline diameters in order to clear the bearings
and ratchet. Further, small cogs typically screw on to the freewheel
body or special cogs with extra threads. This introduces stocking
problems and may make it hard to build some cog combinations.
I'm not a fan of freehubs for the simple reason that they lock me in
to one maker's choices about cogs and cog spacing. For example,
I had
a 1988 Shimano 6-speed freehub and by 1991 Shimano had, according to
my
local bike store, discontinued 6-speed replacement cogs. Thus,
simply
replacing one worn cog meant upgrading to a 7-speed system, which in
turn requires all new cogs, a new freehub body (lucky me -- for some
it
requires a new hub and thus new wheel), and, if I wanted to keep index
shifting, new thumbshifters. Had this been a freewheel-equipped
bicycle, I could have easily switched to another maker's 6-speed
freewheels.
Fortunately, the market is stablizing, with a growing number of makers
producing hubs and cogs using a spline pattern like the more recent
Shimano 7-speed freehubs. However, it hasn't settled entirely,
yet.
;-D oN ( A hubalaboo ) Pardo
------------------------------
Subject: 8.44 "Sealed" Bearings
From: Jobst Brandt <jbrandt@hpl.hp.com>
> Has anyone had any major problems with the Shimono XT "sealed" Bottom
> bracket besides me?
This subject comes up often and has been beat around a bit. There
is a
basic misconception about seals. The seals commonly sold in the
bicycle
business are not capable of sealing out water because they were never
designed for that purpose. These seals are designed to prevent
air from
being drawn through the bearing when used in, typically, electric motors
where the motor rotation pumps air that would centrifugally be drawn
through the bearing. If this were permitted, the lubricant would
act as
fly paper and capture all the dust that passes, rendering the lubricant
uselessly contaminated.
Seal practice requires a seal to leak if it is to work. The seepage
lubricates the interface between shaft and seal and without this small
amount of weeping, the seal lip would burn and develop a gap.
In the
presence of water on the outside, the weeping oil emulsifies and
circulates back under the lip to introduce moisture into the bearing.
This is usually not fatal because it is only a small amount, but the
displaced grease on the lip dries out and leaves the lip unlubricated.
The next time water contacts the interface, it wicks into the gap by
capillary action and begins to fill the bearing. This is an expected
result for seal manufacturers who live by the rule that no two fluids
can be effectively separated by a single seal lip. Two oils,
for
instance, must have separate seals with a ventilated air gap between
them. If a seal is to work with only one lip the contained fluid
must
be at a higher pressure so that the flow is biased to prevent
circulation.
None of the effective methods are used in the so called 'sealed'
bearings that Phil Wood introduced into bicycling years ago.
His
components failed at least as often as non sealed units and probably
more often because they make field repair difficult. These are
not
liquid seals but merely air dams.
jbrandt@hpl.hp.com
------------------------------
Subject: 8.45 Installing Cranks
From: Jobst Brandt <jbrandt@hpl.hp.com>
> My cranks get loose, quite quickly too; over about 10 miles or so
> from being solid to flopping about in the breeze. Any suggestions?
Your cranks are ruined! Once ridden in the "floppy" mode, the
square
taper in the crank can no longer be secured on the spindle. Get
some
new cranks and properly tighten them after lubricating the tapers.
Proper tightness can be guaranteed only by torque wrench or a skilled
mechanic. The second of these is less expensive and you might
be able
to get a demonstration of what is tight enough.
The admonition to not lubricate the tapers of the crank spindle seems
to find life only on bicycle cranks, of all the machines I have seen.
I have pursued the "dry assembly" instruction by talking to crank
manufacturers and discovered that they apparently had warranty claims
from customers who split their cranks open. It is easy to prove
that
cranks cannot split by over-tightening simply by attempting to do so.
It is not possible to split a major brand crank this way, the bolt
will fail first.
Crank failure from "over-tightening" is caused by the re-tightening
of
previously properly installed cranks. Once installed, a crank
always
squirms on its taper, and because the retaining bolt prevents it from
coming off, it elbows itself away from the bolt and up the taper ever
so slightly. This can be detected by the looseness of the retaining
bolt after the bicycle has been ridden hard.
Grease in this interface does not affect performance, because only the
press fit, not friction, transmits load from crank to spindle.
As any
bicycle mechanic can tell you, crank bolts are often appreciably
looser after use, the left one more so than the right. This occurs
because the left crank transmits torque and bending simultaneously
while the right crank transmits these forces one at a time. The
right
crank puts no significant torque into the spindle. Either way,
the
looseness occurs because loads make the crank squirm on the spindle
and the only direction it can move is up the taper, the retaining bolt
blocking motion in the other direction.
Regardless, whether grease or no grease is used, in use the spindle
and crank will make metal to metal contact and cause fretting
corrosion for all but the lightest riders. The purpose of the
lubricant is to give a predictable press fit for a known torque.
If
the spindle is completely dry this cannot be said, and even with
marginal lubrication, some galling may occur on installation.
Lubrication is only used to guarantee a proper press because the
lubricant is displaced from the interface in use. Taper faces
of
spindles show erosion and rouge after substantial use, evidence that
the lubricant was displaced.
"Dust caps" aren't just dust caps but retention for loose bolts.
It
is not that the bolt unscrews but that the crank moves up the taper.
However, once the screw is unloaded it can subsequently unscrew and
fall out if there is no cap.
Because cranks squirm farther up the taper when stressed highly, the
unwitting mechanic believes the screw got loose, rather than that the
crank got tighter. By pursuing the crank with its every move
up the
spindle, ultimately the crank will split. It is this splitting
that
has been incorrectly diagnosed as being caused by lubrication.
I have
never seen a warning against re-tightening cranks after having been
installed with a proper press fit. It is here where the warning
belongs, not with lubrication.
For the press fit to work properly, the pressure must be great enough
to prevent elastic separation between the crank and spindle under
torque, bending, and shear loads. This means that no gap between
crank and spindle should open when pedaling forcefully. Friction
has no effect on the transmission of torque because the crank creeps
into a position of equilibrium on the spindle in a few hard strokes.
Failure of this interface occurs when the press fit is too loose
allowing a gap open between spindle and crank. Torque is transmitted
by the entire face of the press fit, both the leading edge whose
contact pressure increases and the trailing edge whose contact
pressure decreases. If lift-off occurs, the entire force bears
only
on the leading edge and plastic failure ensues (loose crank syndrome).
Tightening the retaining screw afterward cannot re-establish a square
hole in the crank because the retaining screw will break before the
spindle can exert sufficient stress to reshape the bore. Beyond
that,
the crank would split before any plastic deformation could occur even
if the screw were sufficiently strong.
Because retaining screws could become entirely lose from squirming
action, especially if the press is relatively light, "dust caps"
should be used to prevent screws from subsequently unscrewing and
causing crank bore failure. Besides, the loss of the screw won't
be
noticed until the crank comes off, long after the screw fell out.
The argument that the greased spindle will enlarge the hole of the
crank and ultimately reduce chainwheel clearance is also specious,
because the crank does not operate in the plastic stress level.
At
the elastic limit it would break at the attachment knuckle in a short
time from metal fatigue, that occurs rapidly at the yield stress.
In
fact, the depth of engagement (hole enlargement) can increase with
an
unlubricated fit faster than with a lubricated one, because
installation friction is the only mechanism that reams the hole.
Jobst Brandt <jbrandt@hpl.hp.com>
------------------------------
Subject: 8.46 Stress Relieving Spokes
From: Jobst Brandt <jbrandt@hpl.hp.com>
> I wonder if "stress-relieving" is entirely correct? I see it
as a
> yielding/hardening process, in which the yield load is increased
by
> embedding the spoke elbow in the hub, bending the elbow to a different
> angle, etc. When unloaded from a high load, this area of the
spoke
> should be more or less elastic.
> So I think the term should be "overloading" or "hardening" -- any
> thoughts??
Yes. I am certain that the concept of stress relieving is obscure
to many
if not most people because after seeming to understand it, comments
like
this one surface.
A spoke is cold formed from wire that is (at least DT) as hard and
work hardened as it will get. The process after tensioning a
wheel
does not further harden the spokes. The wire is straightened
by
running it through staggered rollers in X and Y directions. The
rollers have, like a degausser, ever diminishing excursions.
This
gets rid of the natural curl left from being shipped in a coil.
If
the wire was not curled before winding it would be a dangerous weapon
on the spool because if the end got loose, all hell would break loose,
making a huge birds nest.
Anyway, the straightening process leaves the spoke with internal
stresses that are well balanced and relatively low. I haven't
given
this a lot of thought but it seems that if there were a large number
of rollers, the stress might approach zero. After this process,
the
spoke gets its head forged on is cut to length, threaded and, and
lastly its head is crudely but accurately knocked to one side to
produce the elbow.
The threads, head, and elbow, contain metal that went beyond yield as
well as metal that did not. The metal in these zones is stressed
one
part against another, one wanting to return to the condition before
or
during forming, and the other to the formed shape. On lacing
the
spokes into a wheel, the elbow is additionally bent (brought to yield)
and upon tensioning this stress remains at or reaches the yield point
it if it wasn't already there. The threads, that have locked
in
stresses (all stresses are ultimately tension and compression) is
selectively stressed at the contact points with the nipple thread and
in tension in the core that already was in tension because thread
rolling stretches this portion of the spoke slightly.
The result is that a freshly built wheel has spokes locations where
stress is guaranteed to be at the yield point. If used this way,
the
cyclic load with each wheel revolution will cause spokes to fail in
fatigue at these high stress points. The load on the wheel only
unloads spokes but because the spoke is operating up to the yield
point, it cannot withstand many stress cycles. The greater the
load
(unloading) the sooner it will fail because when operating close to
the yield stress a metal cannot survive. Only the lightest riders
who
ride smooth roads might not experience failures.
The purpose of stress relieving is to relax these high stress points
in the spokes. The purpose is not to bed the spokes into the
hub.
Bedding in has usually already occurred sufficiently for practical
purposes during tensioning. By stretching each spoke with a strong
grasp, its tension can be temporarily increased by 50 to 100%.
Because a spoke operates at about 1/3 its yield stress, this operation
has little to no effect on the spoke as a whole. Stress relieving
affects only the microscopic zones of the spoke that are at high
stress (near or at the yield stress). By stretching these zones
and
relaxing the load afterward, the margin to yield is as much as the
overload or more.
A whimpy grasp of the spokes during stress relieving is close to
worthless and dropping the wheel, bending it in a partially opened
drawer, pressing on the rim with the hub on the floor and the like
is
as close to useless as you can get. The only method that I have
seen,
but do not recommend, is walking on the wheel while wearing tennis
shoes and carefully stepping on each pair of crossed spokes.
The problem
with this is that it bends the rim and it is difficult to be sure each
spoke gets a good stretch.
IT IS STRESS RELIEVING! At least that's what I am referring to
by the
term.
Jobst Brandt <jbrandt@hplabs.hp.com>
------------------------------
Subject: 8.47 Traffic detector loops
From: Bob Shanteau <shanteau@iname.com>
A traffic loop detects metal objects such as cars and bicycles based
on
the change in inductance that they induce in the loop. The loop is
an
inductor in an LC circuit that is tuned to resonate at a certain
frequency. A metal plate over the loop (like a car) causes the magnetic
flux to be shorted, reducing the inductance of the loop. This causes
a
change in resonant frequency, which is detected and sent to the signal
controller. One of the ways of testing a loop is to create a loop about
2 feet in diameter with several turns of wire (connecting the ends)
and
placing the test wire in the middle of the traffic loop. The test wire
should cause a dectection, if all is working.
The same effect is seen with a vertical piece of metal, such as a
bicycle, but is weaker. Because aluminum conducts electricity quite
well, aluminum rims help. Steel rims are OK. Non-metal rims cannot
be
picked up at all. A bicycle with aluminum rims will cause about 1/100
the change in inductance of a car.
It is always possible to set a detector's sensitivity to pick up a
bicycle. The trade-off is in longer detection times and the possibility
of false detections from vehicles in adjacent lanes. Most people who
set
signal detectors use the lowest sensitivity setting that will pick
up
cars reliably.
I advocate using the highest setting that will avoid picking up vehicles
in adjacent lanes. Digital circuits used in modern detectors can use
high sensitivity settings without unacceptable increases in detection
times. Unfortunately, there are still a lot of old detectors out there,
and most people who work on signals use principles based on the
performance characteristics of old detectors.
In any case, bicyclists should, as a general rule, place their wheels
over one of the slots to maximize their chance of being detected. That
is where the magnetic field perpindicular to the wheels is strongest.
Bouncing the bike or moving it back and forth does no good. If you
have
a metal frame, another tactic that may work is to lay the bicycle down
horizontally inside the loop until the light turns green.
Advancements are under way that may make traffic loops obsolete some
day. In particular, radar, infrared and sound detectors have been
introduced. Systems based on video cameras are especially promising.
Such systems can easily detect bicycles. Such a system may even be
able
to detect pedestrians some day.
Bob Shanteau, PhD. PE
Registered Traffic Engineer
------------------------------
Subject: 8.48 Gluing Sew-up Tires
From: Roger Marquis <marquis@roble.com>
[More up to date copies of Roger's articles can be found at
http://www.roble.com/marquis/]
Davis criterium, it's hot, hot, hot. The pace is fast and
the
corners sharp. Inevitably some riders are going to roll tires,
happens every year. What can you do to insure that your sew-up
tires stay glued when the mercury rises?
There is no one cause of poor tire-rim adhesion so let's start at
the beginning, new rims and tires. Most rims are shipped with
a
coating of anti-corrosive substances that closely resemble grease.
This has to be thoroughly removed with solvent and a clean rag
before you can put down the first coat of glue. Fast Tack is
not
the best glue to use on a bare rim. Instead try Clement, Wolber
or
one of the other slower drying glues. Put a thin coat of glue
all
the way around and leave the wheel(s) to dry for at least 12 hours.
While this glue is drying you might check your tires for any latex
that might be covering the base tape. If there is any latex at
all
give it a good roughing up with coarse sandpaper before coating it
with a thin layer of standard glue or Fast Tack. This too should
be left to dry for a few hours. If you're a light rider or don't
plan on doing any hard cornering on hot days you can usually leave
out this step but always roughen the latex on the base tape.
After the base coat of glue has dried it's time for the adhesive
layer. This should be thicker than the first layer but not so
thick that it can squeeze out from under the tire when you mount it
and get on the rim and sidewalls. If you are using a traditional
style road glue let it dry for ten to fifteen minutes before
putting your tires on. Tires should be mounted on Fast Tacked
rims
immediately.
New tires usually need a good stretching before they will go onto
the rim without tending to roll and get glue all over them. I
usually stretch a tire by pulling it around my knees and feet for
a few seconds and then mounting it on an old rim for a while.
You
might want to try mounting the tire on a dry rim first to see just
how much stretching it will need.
If you used traditional sew-up glue you should wait at least 12
hours before doing any serious cornering. If you need to race
right away you can use Fast Tack and corner confidently within an
hour. Be sure to spread the glue evenly over the surface of the
rim using your finger or a brush. To get the last section of
tire
onto the rim without making a mess grab the remaining 3 or 4 inches
and lift the tire away from and over the rim. This can be
difficult if you forget to stretch it beforehand.
Some glues work better than others in hot weather. Fast
Tack works
best followed by Wolber and Vittoria with Clement in the middle and
Tubasti at the bottom of the list.
When buying Fast Tack be sure you get the real thing. 3-M
sells
other trim adhesives in boxes nearly identical to Fast Tack.
These
trim adhesives do not work for bicycle tires! Be careful that
whatever glue you do use has not separated in its tube. If it
has,
take a spoke and stir it up before you squeeze it out. I have
also
heard of mixing different glues before application. This is a
dangerous shortcut that yields unpredictable results. Fast Tack
and Clement are the most popular tire adhesives. Even though
Fast
Tack will dry out you can get a few tire changes between
replications if you have a good layer of traditional glue on the
rim underneath it. Racing tires though, should be reglued each
time. Base tapes can come apart from the tire in hot weather
and
underinflation can cause tires to roll as well. Check these things
as well as the tread for wear or cuts before every race and you'll
be able to descend and corner with confidence.
Roger Marquis (marquis@roble.com)
------------------------------
Subject: 8.49 Common Torque Values
From: Mike Iglesias <iglesias@draco.acs.uci.edu>
These torque values are from the Third Hand catalog. All values
are in
inch pounds (in lbs); to convert to foot pounds (ft lbs), divide by
12.
Stem binder bolt
100-120 Brake levers to handlebars 75-95
Handlebar binder
145-200 Brake cable binders
55-75
Controls to frame
35-45 Straddle nut (yoke)
50-70
Front shifter to frame
25-45 Brake pads to brake
45-75
Front shifter to cable binder 25-45 Brake dome
nut
50-80
Rear shifter to frame
120-145 Crank bolt
250-300
Rear shifter cable binder 25-45
Chainring bolts
100-120
Jockey wheel bolt
25-45 Nutted front hub
180
Seat binder bolt
35-55 Nutted rear hub
300
Caliper brakes to frame 100-120
Waterbottle cage
25-35
Cantilever brake to frame 45-60
Fender to frame bolts 50-60
Cantilever brake link wire 35-45
Toeclips to pedals
25-45
Kickstand
60
------------------------------
Subject: 8.50 Measuring the circumference of a wheel
From: Jobst Brandt <jbrandt@hpl.hp.com>
For accuracy, the speedometer wants to know how far the bicycle
travels per wheel revolution (under normal load and inflation).
Therefore, that is what must be measured, and it is commonly called
the "rollout distance". To make this measurement, sit on the
bicycle
in typical riding position next to a wall for support, and roll
forward, starting with the valve stem exactly at the bottom at a mark
on the floor. When the stem is again exactly at the bottom, measure
the distance traveled. Typically this distance, for a 700-28
tire at
120 lbs pressure, can be as much as 30 mm shorter under load than
rolling the unloaded wheel for one revolution.
------------------------------
Subject: 8.51 Tubular Fables
From: Jobst Brandt <jbrandt@hpl.hp.com>
> Why is it better to deflate tubulars between rides or is this just
a
> silly rumor?
Yes and no. The "rumor" arises from a misunderstanding.
Track tires,
and these are most often still tubulars, are generally inflated to
more than 10 bar and are dangerous if they were to explode. Good
track tires, unlike road tires, are often made of silk with fine and
thin strands that are not coated or otherwise protected.
I have seen these tires get touched by another rider's pedal and
explode, or even when carelessly laid on any angular object, they can
burst because only breaking a few cords is enough to start a burst.
For this reason track tires are best deflated to less than half their
running pressure when not in use. I can still vividly hear the
sound
of a tire exploding in an indoor track although I heard it only a few
times years ago. It is not something you would like to have happen
in
your car or room.
The reasons people give for deflating tubulars are generally false and
are given for lack of understanding. This is what makes it sound
like
an old wive's tale. Most people do it just to be doing what they
think is "professional" when in fact the protected sidewalls and
pressure of road tubulars makes deflation as meaningless for them as
it is for clinchers.
------------------------------
Subject: 8.52 Folding a Tubular Tire
From: jbrandt@hpl.hp.com (Jobst Brandt)
Date: Thu, 08 Aug 1996 15:31:33 PDT
Although there are many arcane folds that people devise, it boils down
to pragmatism. Most spares are used tubulars because those who
use
them typically ride together and for a new rider someone offers a
spare that gets returned or not at some later time. Therefore,
we are
talking about a previously glued tubular and the point is to prevent
the whole tire from getting goo all over the tread and sidewalls, so
you flatten the tire against itself lengthwise with the sticky base
tape stuck to the sticky base tape. Now you have about a 40 inch
long
flat tire that when folded in half twice makes the typical wad that
riders carry under their saddles secured by a footstrap.
Footstraps being nearly extinct, I don't know what people use today,
but whatever it is, it must be tight and secure. If it isn't,
the
tire will jiggle enough to abrade the sidewalls to become a
pre-packaged blowout, to be installed when you get a flat on the road.
Don't do it. Most spare bags sold today are not good places to
put a
tubular tire because they will allow the tire to vibrate too much.
It's bad news to ride alone with one spare anyway, so you ought to
ride with other tubular riders when you go any significant distance
from appropriate tire service. It's not like carrying a tube
and
patch kit that can go until you run out of patches (you can cut
patches in half too). The advantage of using tubulars is so marginal
that the little weight saved is best applied to track and criterium
racing where its minuscule reduction in rotational inertia can at
least be argued to have some significance.
------------------------------
Subject: 8.53 Frames "going soft"
From: jbrandt@hpl.hp.com (Jobst Brandt)
Date: Mon, 20 Apr 1998 15:31:32 PDT
> I have read accounts of "frames going dead" in cycling literature
in
> the past. If you have information that debunks this, I'd like
to
> know about it. The explanations I have read claim that the
flexing
> of a metal causes it to heat up and harden, making it more brittle.
> Eventually it will break under stress. In fact, I read recently
> that aluminum frames are coming out with warning stickers stating
> "this frame will break someday". I have also read that this
happens
> to titanium and steel.
It was in print, therefore it is true! Also known, is that a freshly
washed and polished car runs better. Just the idea that the car
is
admirably clean makes this concept appear true for many drivers.
The
same psychosomatic mechanism is at work when a bicycle racer thinks
it
is time for a new frame. I even suspect that some frame builders
assisted in spreading this idea to improve frame sales.
Metal fatigue and failure occur, but they do not change the elastic
response of the metal. Steel (and of course aluminum and other
common
metals) have been metallurgically characterized over more than a
century to a precise understanding. None of this research has
shown
the possibility of perceptible change in elastic response from any
stresses to which a bicycle frame might be subjected.
You mention brittleness. Brittleness describes the failure mode
of a
material and is not a perceptible unless the material breaks.
Hardness is also not perceptible unless you exceed the elastic limit
and permanently bend the frame, exposing the metal's yield point, the
point at which it no longer rebounds. If not, it springs back
unchanged as do most ceramics such as a dish, or a glass that is
dropped without breaking. If it breaks, it does not bend and
none of
the shards show any distortion. It either breaks or it doesn't.
That's brittleness personified.
What escapes the believers of material change is that neither
"softening" or "hardening" effects the elastic modulus of the metal.
A coat hanger and a highspeed steel drill of the same diameter have
the same elastic bending stiffness. For small bending deflections,
both are equally stiff, although the hardened steel can bend farther
than the soft steel and still spring back unchanged. The stress
at
which it permanently deforms is the measure of "hardness" of the
metal, not its elasticity.
Classically, when bicycle parts or frames fail, the rider usually
notices nothing before hand. This is true for most thick cross
section parts and often even frame tubes frames. The reason for
this,
is that to permit any perceptible change in deflection, all the added
elasticity must come from a crack that has practically no volume.
So
the crack would need to open substantially to, by itself, allow
perceptible motion. Since this is not possible without complete
failure, the crack grows in length, but not width, until the remaining
cross section can no longer support the load, at which time it
separates.
> If these ideas have been widely disproven, I'd appreciate knowing
> how. I've read all six parts of the FAQ and did not see it
mentioned.
The reason this was not in the FAQ may be that the whole subject is
so
preposterous to engineers, metallurgists, and physicists, that they,
the people who might explain it, are generally not inclined to bother
discussing whether "the moon is made of green cheese" or not.
> PS. If what you're objecting to is the use of the word "dead" as
> opposed to brittle and inflexible, I'll grant you that.
The objection is that you present something for which there is no iota
of scientific evidence, nor any even slightly credible explanation,
as
though it were fact. It is as though bicyclists have a different
natural world, where the technical laws are entirely different from
all other machinery, and the most perceptive technical insights come
from the strongest bicycle racers. "After all who knows more
about
bicycles, you or the world champion?" is a common retort.
Jobst Brandt <jbrandt@hpl.hp.com>
------------------------------
Subject: 8.54 Inspecting your bike for potential failures
From: richkatz@cruzio.com (Keith Bontrager)
Handlebars are probably the one component that deserves the most
respect. Easton recommends a new bar every two years. I
don;t recall
if they include an "if you race" preface. I'd say that's probably
about right. Same for our aluminum bars. Yearly would be
good
on bars that have not been engineered for extended fatigue lives.
Of course, if you don;t race, if you have more than one bike, if
you are a smooth rider, if you like to do "skyshots" you need to
work this in to the estimate. Getting tougher, eh? Many
people
could ride on the good quality bars into the next millenium without
a problem. How do you sort it out? I don't know.
Many parts (not bars or forks) will give you ample warning if you bother
to inspect your bike regularly. Clean it. Look at it.
There
are "hot spots" all over the bike that deserve carefull attention.
Fork crown. Welds if a rigid fork, crown material if its a sus fork.
Steerer. Hard to look at, but once a year, especially if it's
aluminum
or if you've crashed hard with a big front impact. Also if there
are
noises from the front of the bike when you climb or sprint, or
if the bike starts handling funny. Be careful when you change
lower
head set races so you don't gouge up the steerer at the bottom.
If you have an AHS stem/steerer look at the steerer at the point
where the stem and HS bearings meet. Critical!
Stem. All of the welds and the binder. Especially if you
are
a 200lb sprint specialist.
Down tube/head tube joint of the frame - underneath.
Top tube/ head tube joint - same location.
Seat tube - near the BB shell and near the seat binder clamp slot.
BB spindle. Hard to look at, but once a year. Look near
the tapers
where the crank fits on. This is the weak spot. If the
crank
feels funny when you are pedaling (hard to describe the feeling)
or if it comes loose unexpectedly, look long and hard at the spindle.
Cartridge BBs that allow you to change the bearings should be
treated with some respect. You can keep fresh bearings in them
forever, guaranteeing that they'll be in service until the
spindle fails!
Cranks. Check the right hand arm all around where the arm leaves
the spider. Also check the hub where the arm attaches to the
spindle - especially if the arm is machined from bar (CNC). The
section near the pedal threads was prone to failure on older
road cranks though I have not seen this on MTB cranks (yet!).
Look all over the arms on the light aftermarket cranks. Often.
Twice.
Seat post. Pull it out and sight down the quill. Any ripples
or deformation around the area where the post is clamped in the
frame indicates a failure on the way. The clamps are too varied
to
comment on. If you have to run the fasteners real tight to keep
the saddle from slipping you should put new, very high strength
fasteners in every year or so. The clamps can come loose from
the
quill tube sometimes (ask me how I know). Grab the saddle and
give it
a twist.
Saddle. Rails near the seat post support pieces.
Rims. material around spoke holes can pull out, side walls can
wear through, side walls can fail due to extrusion defects. Some
of these are hard to see.
Frames around the dropouts (not a problem with newer frames as it
was with older campy forged drops). Chainstays near the CS bridge
and BB shell.
Hubs. Flanges can pull away from the hub body. Not a problem
in most cases unless the wheels are poorly built, you are running
radial spokes and ride real hard, have poorly designed aftermarket
hubs, or are very unlucky.
Many components will make a bit of noise or make the bike feel funny
before they go. Not all will. Respect this.
------------------------------
Subject: 8.55 ETRTO numbers for tire sizes
From: Osman Isvan <osman_isvan@bose.com >
There is nothing wrong with tire/rim compatibility. If
we...stop calling them with colloquial names such as "26 inch
wheel", "road wheel", etc., we would be all set.
There is no dimension on a mountain bike rim that is even
close to 26 inches. The ETRTO number, bead diameter in
millimeters, is *molded* on the sidewall of the tire (to make
mislabeling almost impossible) and if it matches, it will
match. There is nothing confusing, mysterious or misleading or
complicated about the ETRTO designation. The ETRTO designation
also includes the width of the tire to be sure it is not too
narrow or too wide for the rim, but this dimension is not
accurate as it is not critical.
Common standard bead diameters are 559 mm (ATB), 571 mm
(Triathlon) and 622 mm (road). They are a reasonable size
smaller/larger than each other, so what's the problem?
The confusion comes from us (marketers and consumers)
referring to both the 559 and the 571 standards, and a slew of
others, as 26" for some reason. The term "26 inch wheel"
refers to the approximate outside diameter of the inflated
tire, and has nothing to do with tire/rim compatibility...
This is no different with cars, but in automotive "lingo" the
colloquial names for wheel sizes are the rim diameter (and
that's what matters for compatibility), not the tire outside
diameter. The same car comes with either "13 inch" or "14
inch" wheel options but the outside diameter of the tire may
be the same. The rubber part takes up the difference.
Motorists refer to their RIM SIZE when they talk about wheel
diameter. A 13 inch tire such as "175/70 R 13" means it will
fit to a 13 inch rim.
We should do the same. It is possible to build the same
outside diameter by either using a 26 mm wide tire and 559 mm
(mountain) rim (ETRTO 26-559) or a 20 mm wide tire on a 571mm
(triathlon) rim (ETRTO 20-571), and this doesn't imply they
would be interchangeable. And because the 559 mm (Mountain)
rims have a diameter of only 22 inches, it takes very fat 2.0
inch (Mountain) tires to bump them up to 26". Of course they
wouldn't accept skinny triathlon tires of same thread
diameter.
When ordering tires, order according to bead diameter (ETRTO
designation). This will solve any problems with compatibility.
If the salesperson doesn't understand, ask to look for the
number which is molded with the casing.
------------------------------
Subject: 8.56 Using a Quick Release
From Mark Irving <mhi@uk.gdscorp.com>
The odd-looking thing which attaches most front wheels, many rear wheels
and some seatpins is not a sort of wingnut. It is a quick release
lever.
If it is not properly fastened, your wheels are loose. If this
description
isn't clear, go to any bike shop or find any local bikie person and
get
them to show you. It's hard to describe, not obvious until you've
done it
yourself, and it is important to get right. It's easy when you
know how --
road racers can get their wheels changed in five seconds!
1. Make sure the floppy lever is pushed over to its "OPEN" side.
This
lever operates a cam to close up the 'skewer' later.
2. Loosen off the little nut on the other end of the skewer just
enough to
get the wheel into the dropouts in the frame. Slide the wheel
into the
frame, and balance it there while you do the next bits.
3. With one hand, hold the operating lever straight out (parallel
to the
axle), halfway between OPEN and CLOSED. With the other hand,
tighten the
nut opposite until you feel resistance.
4. Push the operating lever over to CLOSED. This should
be a tough
operation, if you've got the nut adjusted right. It should not
hurt, but
it should leave a dent in the palm of your hand for ten to twenty seconds
afterwards! If you have the tension right, the wheel is now very
safely
and solidly held.
5. If the lever really won't close all the way, open it (the full
180
degrees to OPEN), loosen the nut about 1/4 turn, and go back to step
4. If
it closes all the way without much resistance, open it all the way,
tighten
the nut 1/4 turn, and go back to step 4.
If your bike doesn't have the stupid bumps, clips and 'lawyer lips'
often
added, you'll never need to adjust the nut again. The only action
needed
is to flip the lever between CLOSED and OPEN.
The subtle extra is to point the Q-R lever down, towards the ground,
in its
CLOSED position, so that it doesn't get caught on anything solid when
you're riding. This is infinitely less important than doing it
up
properly.
------------------------------
Subject: 8.57 Tube and Tire Casing Repair
From: John Forester <JForester@cup.portal.com>
There sure seems a dearth of knowledge about patching both tubes
and
casings.
Yes, the idea that tubes could be patched without liquid cement
was a
good idea, but only as an idea to research to see whether an adequate
adhesive could be developed. So far as I know, all the peel and stick
adhesives are very viscous liquids. That means that they don't harden
and
therefore that the air pressure will slowly leak into and through them.
If
the viscosity is high enough it will take the air under pressure a
long
time to form another leak. A glueless patch of the peel and stick variety
cannot have effective solvents in it, because the solvent would evaporate
during storage. Even if the patch were sealed inside a container that
prevented the evaporation of the solvent, the system would have the
problem
of getting enough glue onto the tube and then letting the solvent partially
evaporate from the open joint for the joint to be made. You might as
well
use the old system.
The problem that some experience is that they find the cement hardened
in
the zinc dispensing tube. The answer to that is to buy the cement and
its
solvent in bulk and carry a small quantity in a small jar with a screw
cap.
A metal jar would be most useful, but I do not know of any common source
for
such. Small glass jars are commonly available and last well enough.
Periodically, examine the cement inside and top up with solvent if
it gets
too thick. Because the cement tends to glue the cap to the jar, it
is
desirable to wrap both the jar and the cap with several layers of adhesive
tape to provide a better gripping surface at a larger radius.
Two kinds of cement are available. The traditional cement is rubber
cement,
Camel #12-086 Universal Cement, available at tire shops. The other
cement is
contact cement, available from hardware stores. While the modern
formulations often are non-flammable and use chlorinated hydrocarbons
as
solvents, buy the flammable kind, if available, because the chlorinated
hydrocarbons are detrimental to rubber. (Very important for diluting
rim
cement for tubular tires. Not so important for just tire patches or
boots
because the solvent evaporates.) In any case, use toluol as the replacement
solvent, available at hardware stores.
The tube must be cleaned before applying the cement. Stick medium sandpaper
to tongue depressors and cut to lengths that fit your patch kit.
Cut casings are repaired with an internal boot. Satisfactory
boots are
made from cotton trouser fabric or from lightweight dacron sail fabric.
These must be cemented by contact cement, not tube cement. Cut pieces
of
suitable size, so that they run almost from bead to bead when laid
inside
the casing. Coat one side with several layers of contact cement and
let it
dry completely before storage. Before applying, coat the inside of
the casing with contact cement and press the boot into place before
the
cement dries. Wait about ten minutes before inflating the tire. If
you wait
too long, the cement really hardens and there will be a narrow spot
in the
casing because of the greater strength where the patch reinforces the
casing.
It is probably possible to use contact cement as the tube patch
cement.
Do not use tube cement for boots; it slowly creeps and allows the boot
to
bulge. So carry a small jar of each cement, or one of contact cement.
Contact cement is suitable for closing the outside of the cut
also, but
it must be applied in several layers and allowed to dry thoroughly
before
use, or it will pick up particles from the road. Duro Plastic Rubber
is a
thicker black rubber paste that can be applied in one layer and left
to
harden.
------------------------------
Subject: 8.58 The Continuously Variable Transmission
From: Jobst Brandt <jbrandt@hpl.hp.com>
The Continuously Variable Transmission (CVT) is the holy grail of many
inventors who are not convinced that it is an impossibility.
That is
to say, the positive engagement, continuously variable transmission,
that does not rely on friction, electrical, or hydraulic ratios but
uses mechanical gearing, is not possible.
The CVT does not exist, and I am convinced it will not. If it
were
possible, railway locomotives, trucks, buses, and cars would long ago
have used them. Strangely, it is in bicycling that the strongest
believers of the concept reside... as if there were more money to be
made in bicycles or some such notion. In fact, the bicycle with
its
enormously adaptable human motor doesn't need a CVT. In addition,
its
low input speed and extremely high torque, make the bicycle one of
the
most difficult vehicles to equip with gearing. For this reason
it
uses derailleur chain drive, that is found practically nowhere else.
------------------------------
Subject: 8.59 Patching Tubes
From: Jobst Brandt <jbrandt@hpl.hp.com>
The question often arises whether tubes can be practically and safely
patched. I suppose the question comes up because some people
have had
leaky patches or they consider it an arcane exercise. Either
way, it
need not be difficult if simple rules are followed.
Mold release
Tubes are made in metal molds to which they would stick if mold
release were not sprayed into the mold. The release agent is
designed
to prevent adhesion and it will do the same for patches because it
remains on and in the surface of the tube. To make a patch stick,
this material must be removed. That means, the sand paper in
the
patch kit is not to roughen the surface but to remove it. Not
removing the 'skin' of the tube is a major reason for leaky patches.
Once the mold release has been removed, rubber solution can be applied
with the finger by wiping a thin film over the entire area that the
patch is to cover. After the glue has dried so that no liquid
or
jelly remains, leaving the area with a tacky sheen, the patch should
be pressed into place. Patches can be made from tube material
but
this must be done carefully following the same procedure as preparing
the tube. The trouble is that butyl tube material, unlike patches,
is
impervious to rubber cement solvents and will never cure if the glue
is not completely dry. This presents a substantial problem.
Patches
Patches commonly have a metal foil cover on their sticky side and a
cellophane or impervious paper cover on the other. The foil should
be
pulled off to expose the adhesion surface and the patch pressed into
place. The backing paper or cellophane often has perforations
that
will break if the tube and patch are stretched. This makes peeling
the cover from inside to outside of the patch possible and prevents
peeling a newly installed patch from its position.
REMA patches, the most commonly available in north American bicycle
shops, have a peculiarity that not all have. Their black center
section exudes a brown gas that discolors light colored tire casings
in daylight. This causes the brown blotches often seen on sidewalls
of light colored tires.
Leaky Patches
Assuming the patch was properly installed, it will still possibly leak
after a few miles, if used immediately after patching. Because
the
tube is generally smaller than the space inside the tire, to prevent
wrinkles on installation, it will stretch when inflated as does the
patch. Although it stretches less than the rest of the tube by
the
greater thickness, it resists stretch more than the tube alone.
Under
the patch, the stretched tube tends to shrink away from the patch,
and
because there is no holding force from inflation pressure at the hole,
the tube can peel away from the patch that is held by air pressure.
If the puncture is a 'snake bite', the chances of a leak are even
greater. Pinch flats from insufficient inflation or overload
are
called snake bites because they usually causes a pair of holes that
roughly approximate the fang marks of a snake. These holes are
near
the rim where the contour of the tube is nearly a sharp fold.
This
location is especially susceptible to the tube separation at the hole
closest to the rim.
In a rolling tire, the patch and tube flex, shrink, and stretch making
it easier for the tube to separate from a partially cured patch.
To
test how fast patches cure, a patch can be pulled off easily shortly
after application, while it is practically impossible after a day or
so. For best results, the freshly punctured tube should be patched
and put in reserve, while a reserve tube is installed. This allows
a new patch more time to cure before it is put into service.
A tube can be folded into as small a package as when it was new and
practically airless, by sucking the air out while carefully using the
finger opposite the stem to prevent re-inflation. This is not
done by
inhaling but by puckering the cheeks. Although the powders inside
the
tube are not poisonous in the mouth, they are not good for the lungs,
but then that's obvious.
Minutia
The difficult part of loose patches is that separation always stops
at
the edge of the patch because air pressure prevents further
separation. The annoying intermittent slow leaks that occur,
often
close when the tube is inflated outside a tire, so the offending patch
cannot be found. Old tubes to be discarded often reveal partial
failures by cutting through the center of patches with shears.
Tires are less flexible at a patch and will wear slightly faster
there, but patches have no effect on dynamic balance since wheels are
so imbalanced that patches have no effect on the heaviest position
of
the wheel. Heat from braking can accelerate separation of a fresh
patch but this generally does not pose a sudden hazard because lifting
patches most often causes only a slow leak.
------------------------------
Subject: 8.60 Shimmy or Speed Wobble
From: Jobst Brandt <jbrandt@hpl.hp.com>
Shimmy is not related to frame alignment or loose bearings as is often
suggested. Shimmy arises from the dynamics of forward motion
and the
elasticity of the frame, fork, and wheels, and the saddle position.
Both perfectly aligned bicycles and ones with wheels out of plane to
one another shimmy nearly equally well. The same is true for
bearing
adjustment. In fact shimmy is more likely with properly adjusted
bearings than loose ones. The bearing or alignment concept is
usually
offered as a cause of shimmy and each airing perpetuates the idea.
Shimmy, the lateral oscillation at the head tube, depends primarily
on
the frame and its geometry. The inflation of the tire and the
gyroscopic effects of the front wheel make it largely speed dependent.
It cannot be fixed by adjustments because it is inherent to the
geometry and elasticity of the components. The longer the frame
and
the higher the saddle, the greater the tendency to shimmy, other
things being equal. Weight distribution also has no effect on
shimmy
although where that weight contacts the frame does.
In contrast to common knowledge, a well aligned frame shimmies more
easily than a crooked one because it rides straight and without bias.
The bias force of a crooked frame impedes shimmy slightly. Because
many riders never ride no-hands downhill, or at least not in the
critical speed range, they seldom encounter shimmy. When it occurs
with the hands on the bars it is unusual and especially disconcerting.
There is a preferred speed at which shimmy initiates when coasting
no-hands on a smooth road and it should occur every time when in that
critical speed range. Although it usually does not initiate at
higher
speed, it can.
Pedaling or rough road interferes with shimmy on a bicycle that isn't
highly susceptible. When coasting, laying one leg against the
top
tube is the most common way to inhibit it. Interestingly, compliant
tread of knobby tires give such high lateral damping that most
bicycles equipped with knobbies do not shimmy.
Shimmy is caused by the gyroscopic force of the front wheel that acts
at 90 degrees to the axis of the steering motion. The wheel steers
to
the left about a vertical axis when it is leaned to the left about
a
horizontal axis. When the wheel leans to the one side, gyroscopic
force steers it toward that side, however, the steering action
immediately reverses the lean of the wheel as the tire contact point
acts on the trail of the fork caster to reverse the steering motion.
The shimmy oscillates at a rate that the rider's mass on the saddle
cannot follow, causing the top and down tubes to act as springs that
store the energy that initiates the return swing. The shimmy
will
stop if the rider unloads the saddle, because the mass of the rider
is
the anchor about which the oscillation operates. Without this
anchor
no energy is stored. The fork and wheels may store some energy,
although it appears the frame acts as the principal spring.
Shimmy can also be initiated with the hands firmly on the bars by
shivering, typically in cold weather. The frequency of human
shivering is about the same as that of a typical bicycle frame.
------------------------------
Subject: 8.61 Bike Part Failure Web Site
From: Dave Blake <dblake@phy.ucsf.edu>
Here it is, the web based rec.bicycles.tech failures compilation at
http://www.keck.ucsf.edu/~dblake/fail.html
This list is provided as a service to anyone interested in which
bike parts are most durable.
The failures are collections of first hand accounts of bike parts
that failed in usage that was not beyond the design of the part.
If you have a bike part that failed on you - send the account
in ! ! You can view the accounts of others on the web page above.
------------------------------
Subject: 8.62 Rolling resistance of Tires
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>
Date: Thu, 08 Aug 1996 17:17:57 PDT
The question often arises whether a small cross section tire has lower
rolling resistance than a larger one. The answer, as often, is
yes
and no, because unseen factors come into play. Rolling resistance
of
a tire arises almost entirely from flexural rubber losses in the tire
and tube. Rubber, especially with carbon black, as is commonly
used in
tires, is a high loss material. On the other hand rubber without
carbon black although having lower losses, wears rapidly and has
miserable traction when wet.
Besides the tread, the tube of an inflated tire is so firmly pressed
against the casing that it, in effect, becomes an internal tread.
The tread and the tube together absorb the majority of the energy lost
in the rolling tire while the inter-cord binder (usually rubber) comes
in far behind. Tread scuffing on the road is even less significant.
Patterned treads measurably increase rolling resistance over slicks,
because the rubber bulges and deforms into tread voids when pressed
against the road. This effect, tread squirm, is mostly absent
with
smooth tires because it cannot be bulge laterally by road contact
because rubber, although elastic, is incompressible.
Small cross section tires experience more deformation than a large
cross section tire and therefore, should have greater rolling
resistance, but they generally do not, because large and small cross
section tires are not identical in other respects. Large tires
nearly
always have thicker tread and often use heavier tubes, besides having
thicker casings. For these reasons, smaller tire usually have
lower
rolling resistance rather than from the smaller contact patch to which
it is often attributed.
These comparative values were measured on various tires over a range
of inflation pressures that were used to determine the response to
inflation. Cheap heavy tires gave the greatest improvement in
rolling
resistance with increased pressure but were never as low as high
performance tires. High performance tires with thin sidewalls
and
high TPI (threads per inch) were low in rolling resistance and
improved little with increasing inflation pressure.
As was mentioned in another item, tubular tires, although having lower
tire losses, performed worse than equivalent clincher tires because
the tubular's rim glue absorbs a constant amount of energy regardless
of inflation pressure. Only (hard) track glue absolves tubulars
of
this deficit and should always be used in timed record events.
------------------------------
Subject: 8.63 Blowouts and Sudden Flats
From: Jobst Brandt <jbrandt@hpl.hp.com>
Date: Mon, 26 Aug 1996 16:58:07 PDT
Bicyclists often report tube failures that they believe occurred
inside the tire casing. They believe these are caused by a faulty
tube that split or that the rim tape failed. However, they also
heard
a bang after which the tire was flat. On removing the tire casing
from the rim with tire irons, they discover a burst tube with a large
slash.
If there was an audible bang, then the tire was off the rim. That
the
undamaged tire is still on the rim afterwards proves only that tires
usually fall back into place after exposing the tube. A tube
cannot
blow out inside the tire with a bang, because a bang is caused by a
sudden change in volume, an expansion. Such an expansion is not
possible within a tire casing. Beyond that, the resulting clean
slash
in the tube cannot occur from rim tape that would cause a gradual
failure along an abraded line that extends beyond the end of the
split. A burst into a rime hole would cause a starburst hole
that is
smaller than the rim socket because the tube shrinks when no longer
inflated.
Tire blow-off occurs most commonly on tandems where substantial energy
of descending mountain roads is converted to heat in rims by braking,
in contrast to a single bicycle, where most of the energy is
dissipated by wind drag. Rim heating has two effects, of which
increased pressure is probably the lesser one. Heat softens the
bead
of the tire so that it can squirm out of its clinching seat in the
rim. Tire casing flex at the load point works the tire so that
it
squirms out of engagement. Heat also increases lubricity of the
bead
against the rim to facilitate creep.
Short tubes, that must be stretched to fit on the rim, can cause tire
blow-off. A stretched tube will occupy the space on the bed of
the
rim where the tire bead should be to make proper engagement with the
hook of the rim sidewall. The tube under the bead of the tire
can
prevent proper engagement with a hooked rim to cause a blow-off even
without great heat or pressure.
------------------------------
Subject: 8.64 Tied and Soldered Wheels
From: Jobst Brandt <jbrandt@hpl.hp.com>
Date: Mon, 16 Dec 1996 15:09:03 PST
While writing "the Bicycle Wheel", to conclusively determine what
effect tying and soldering of spoke crossings in a wheel had, I asked
Wheelsmith to loan me an untied pair of standard 36 spoke rear wheels,
on on Campagnolo low and high flange hubs. I had an inner body
of a
freewheel machined with flats so that a wheel could be clamped into
the vise of a Bridgeport milling machine while the left end of its
axle was held in the quill.
With the hub rigidly secured, with its axle vertical, dial gauges were
mounted at four equally spaced locations on the machine bed to measure
rim deflections as a 35lb weight was sequentially hung on the wheel
at
these positions. The deflections were recorded for each location
and
averaged for each wheel before and after tying and soldering spokes.
The wheels were also measured for torsional rigidity in the same
fixture, by a wire anchored in the valve hole and wrapped around the
rim so that a 35 lb force could be applied tangential to the rim.
Dial gauges located at two places 90 degrees apart in the quadrant
away from the applied load were used to measure relative rotation
between the wheel and hub.
Upon repeating the measurements after tying and soldering the spokes,
no perceptible change, other than random measurement noise of a few
thousandths of an inch, was detected. The spokes were tied and
soldered by Wheelsmith who did this as a regular service. The
data
was collected by an engineer who did not know what I expected to find.
I set up the experiment and delivered the wheels.
------------------------------
Subject: 8.65 Tube Failure in Clinchers
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>
Date: Mon, 13 Oct 1997 15:02:23 PDT
Riders occasionally tell about a tube that blew out with a loud bang
INSIDE their tire, leaving the tube with a long slash. The tube
blew
out, but not as described. If there was a bang, the tube was
outside
the tire. That is, the tire lifted off the rim and fell back
in place
after the tube burst.
Tubes do not burst inside tire casings, although they may leak, the
most they can do is give off an audible hiss, assuming it is otherwise
quiet enough. An un-socketed double walled rim can make a dull
pop if
the tube is exposed to the inner rim volume. The concept that
a tube
can explode inside a tire is dangerous, because it leads people to
believe that tubes can mysteriously fail without apparent cause INSIDE
a tire. With few exceptions, the cause is an improperly mounted
tire.
Without understanding the cause, a rider may continue to risk a
blowout, without realizing that tire lift-off can be caused by the
tube lying between the rim and the tire bead. In this position,
the
tube prevents the tire from seating properly in the hook of the rim,
a
condition that, under the right circumstances, will cause a blowout.
This cannot occur inside the tire casing. To prevent blow-off,
the
tire seat must be inspected by pushing the tire away from the rim,
upon which the tube should not exposed at any point around the tire.
Valve stem separation is another common failure, but it is less
dangerous because it usually occurs while inflating the tire.
If it
occurs while riding it causes a slow leak, as the vulcanized brass
stem separates from the tube. When this occurs, the stem can
be
pulled out entirely to leave a small hole into which a valve stem from
a latex tube of a tubular tire will fit. Stems from tubulars
have a
mushroom end, a clamp washer, and a locknut, that fit ideally.
Such a
used stem should be part of a tire patch kit.
------------------------------
Subject: 8.66 Wiping Tires
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>
Date: Mon, 13 Oct 1997 15:02:23 PDT
Although the tire wiping has mostly gone the way of the tubular tire,
some riders have remained believers in this practice, that never had
any validity in the first place. It is purportedly done to prevent
punctures by wiping off glass that may have "stuck" to the tire.
If one considers the rotation rate of a wheel in typical bicycling,
about 15-20mph, it comes to about 3.5 revolutions per second.
When
observing a tire wiper, the time between noticing hazardous debris
on
the road and the first wipe is more than a second. Hence, any
glass
or other small object would be firmly pressed into the tire by four
revolutions and all exposed glass edges chipped off. By the time
the
other tire is wiped several more seconds will have passed. If
the
glass is not thoroughly embedded by then it will not enter the tire.
This is not to say that particles embedded in a tire always cause a
leak immediately, but that they are irrecoverably in the tire at that
time. Those who have patched flats from glass will recall that
the
piece of glass is not easily found, especially if the location of the
puncture is not known. The embedded chip is usually imperceptible
when wiping the hand over the place even when known.
On the other hand, the rear wheel is more subject to flats than the
front, because flat objects must first be tipped up to engage a tire
to have any effect. Wiping the rear tire on common short frame
bicycles is hazardous, because the fingers can be sucked into the
narrow gap between tire and seat tube to cause serious injury.
Carefully considered, tire wiping is an idle gesture, reassuring to
some riders, and impressive to others if deftly executed. I recall
as
a beginner that learning all the tics of bicycle racing was important.
Wiping tires was one of these. Forget it.
------------------------------
Subject: 8.67 Coiling a Wire Bead Clincher
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>
Date: Fri, 17 Oct 1997 10:00:05 PDT
_____________
_________
*/
\*
*/ \*
*/
\*
*| |*
*/
\*
*| |*
*/
\*
*| |*
*|
|* _________*|__________/*
*|
|* */
*|
*|
|* *|
*|
push--> *| pull & turn <-- |*
*| *|
*|
|* *|
*|
*|
|* *\_________*|__________
*|
|*
*| \*
*\
/*
*| |*
*\
/*
*| |*
*\
/*
*| |*
*\_____________/* (*)tread
*\_________/*
Holding the tire seen edge-on in front of you, pull the front half
inward while turning that part so the tread faces you, to make the
figure on the right.
Fold the side loops over one another on top of the central loop.
This
is the way band saws are coiled for storage. The three coil pack
must
be secured to prevent it from springing open again.
------------------------------
Subject: 8.68 Working on a Bicycle Upside-down
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>
Date: Tue, 04 Nov 1997 14:33:14 PST
> Should I continue to turn my bicycle upside-down to fix a flat,
> the way I learned it as a youth?
Nothing can be done to a bicycle upside-down that cannot be done
better with it right-side-up, except to spin the rear wheel while hand
cranking the pedals. In fact, that is what most children do when
they
haven't anything better to do with their bicycles. That is how
I
discovered that a bicycle wheel is not well balanced, because the
bicycle began to hop when I cranked fast. I also found that this
wore
a hole in the saddle, and scratched the handlebars and grips to the
dismay of my parents.
Many riders who have taken up the sport after years off the bicycle,
recall only a few things from their earlier experience, and turning
the bicycle upside-down seems to be one of them. I defy someone
to
show me how they can change a rear wheel easily on an upturned
bicycle, be that with one speed or a derailleur. Even chain removal
is more difficult on the inverted bicycle, but this should be apparent
because no bicycle shop works on upside-down bicycles.
Beside the inconvenience, damage to the saddles, handle bars, and
speedometers is expensive. Warranty claims for damaged speedometers
with cracked LCD's and housings first brought this practice to my
attention, the failures being unexplainable under normal use.
The
solution was to reinforce the speedometer's case so it could support
the load of the bicycle.
The most common explanation for this practice is that there was no way
to keep the bicycle from falling over during a tire change. Laying
it
on its side somehow doesn't seem right, so the bicycle is turned on
its head. It might not look fallen over, but it is worse off.
------------------------------
Subject: 8.69 Talcum Powder for Tubes and Tires
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>
Date: Tue, 04 Nov 1997 16:54:17 PST
> I've been told since my first bike that I should liberally dust the
> tube in talcum powder before installing it. I've believe that
this
> may have reduced the number of flats I've had recently.
Talcum is one of the more durable urban legends. There is no benefit
in putting talcum or substitute powder on a tube or in a tire.
The
practice has come to bicycle tires the same way tire treads that are
miniature replicas of automobile treads have... if it's good for cars,
it must be good for bicycles. Trucks (and formerly cars) use
talcum
or graphite powder between tire and tube, because without it, the two
can vulcanize from the heat of rolling. This often makes tube
removal
destructive, leaving tube fragments stuck in the tire casing.
Bicycles do not generate enough heat to vulcanize tubes, so they can
be removed from the tire without problem. Other than that, talcum
has
no effect on punctures other than to release air faster when one
occurs. A tube stuck to the casing will retain air for a considerable
distance after a thorn penetration because the thorn that penetrates
plugs the casing hole leaving the tube hole with no outlet. This
is
especially true for snake bites. I have found such flats the
day
after when they have gone flat over night. Without powder, a
tube
will stick adequately to most clincher tires in about 100 miles.
Corn starch is no better than talcum powder, the only difference being
that it is water soluble, but then who cares. Talcum also cakes
up
when wet, although it doesn't dissolve.
A tube cannot move in a tire when inflated, regardless of what powder
is used, because, no translational forces exist, on top of which the
holding force between tube and casing is large. That talcum prevents
damage when mounting a tire is also not the case, because the pinch
occurs when the last part of the bead is being popped onto the rim.
This can cause a pinch with or without a tire iron, and powder will
not protect a tube from lying in the gap if it hasn't been pushed into
the tire adequately.
The reason tubes have talcum powder inside is that in manufacture,
they become hot enough that, otherwise, they could become inseparably
stuck when folded. That is why most butyl tubes have talcum inside.
------------------------------
Subject: 8.70 Tires with smooth tread
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>
Date: Fri, 05 Dec 1997 16:29:59 PST
Drag racers first recognized the traction benefits of slick tires,
whose benefit they could readily verify by elapsed times for the
standing start quarter mile. In spite of compelling evidence
of
improved traction, more than twenty years passed before slicks were
commonly used for racing cars, and another twenty before they reached
racing motorcycles. Today, slicks are used in all weather by
most
street motorcycles. In spite of this, here at the end of the
millennium, 100 years after John Dunlop invented the pneumatic tire
for his own bicycle, bicyclists have not yet accepted smooth tread.
Commercial aircraft, and especially motorcycles, demonstrate that a
round cross section tire, like the bicycle tire, has an ideal shape
to
prevent hydroplaning. The contact patch, a pointed canoe shape,
displaces water exceptionally well. In spite of this, hydroplaning
seems to be a primary concern for riders who are afraid to use smooth
tires. After assurances from motorcycle and aircraft examples,
slipperiness on wet pavement appears as the next hurdle.
Benefits of smooth tread are not easily demonstrated because most
bicycle riders seldom ride near the limit of traction in either curves
or braking. There is no simple measure of elapsed time or lean
angle
that clearly demonstrates any advantage, partly because skill among
riders varies greatly. However, machines that measure traction
show
that smooth tires corner better on both wet and dry pavement.
In such
tests, other things being equal, smooth tires achieve greater lean
angles while having lower rolling resistance.
Tread patterns have no effect on surfaces in which they leave no
impression. That is to say, if the road is harder than the tire,
a
tread pattern does not improve traction. That smooth tires have
better dry traction is probably accepted by most bicyclists, but wet
pavement still appears to raise doubts even though motorcycles have
shown that tread patterns do not improve wet traction.
A window-cleaning squeegee demonstrates this effect well. Even
with a
new sharp edge, it glides effortlessly over wet glass leaving a
microscopic layer of water behind to evaporate. On a second swipe,
the squeegee sticks to the dry glass. This example should make
apparent that the lubricating water layer cannot be removed by tire
tread, and that only the micro-grit of the road surface can penetrate
this layer to give traction. For this reason, metal plates, paint
stripes, and railway tracks are incorrigibly slippery.
Besides having better wet and dry traction, smooth tread also has
lower rolling resistance, because its rubber does not deform into
tread voids. Rubber being essentially incompressible, deforms
like a
water filled balloon, changing shape, but not volume. For a tire
with
tread voids, its rubber bulges under load and rebounds with less force
than the deforming force. This internal damping causes the energy
losses of rolling resistance. In contrast the smooth tread transmits
the load to the loss-free pneumatic compliance of the tire.
In curves, tread features squirm to allow walking and ultimately,
early breakout. This is best demonstrated on knobby MTB tires,
some
of which track so poorly that they are difficult to ride no-hands.
Although knobby wheelbarrow tires serves only to trap dirt, smooth
tires may yet be accepted there sooner than for bicycles.
------------------------------
Subject: 8.71 Another way to glue sewup tires
From: "Mike & Joanna Brown" <mjbrown1@airmail.net>
Date: Wed, 06 May 1998 21:49:53 CDT
I have been racing for 6 years now and have tried multiple tire/rim
combinations. I have come to the conclusion that good tubular
tires on a
pair of good carbon fiber rims provide the ultimate ride. But
many people
dislike tubular tires because of the gluing process and the possibility
of
rolling the tire during fast cornering.
I decided to write this article because of the three to four racers
who
rolled a tire at the recent Baylor/Mirage sponsored criterium.
Rolling a
tire at anytime during race can be catastrophic. Everyone has
their "best"
way of gluing a tire. I can assure you, this is by far the best
and SAFEST
way to glue a tire to prevent it from rolling during any type of cornering
at any speed. I took this process out of Cycling USA last year
and now
follow it religiously when gluing my own tires. This gluing process
was
far superior to the manufacturers recommended process in regards to
bond
strength at tire/rim interface. We will briefly discuss the following;
1)
The glue 2) Mounting tubulars to new rims 3) Mounting tubulars to used
rims.
Not all glues are the same. Especially in Texas! The temperature
outside
may be 90 to 100 degrees, but the surface you are racing on may be
150 to
160 degrees. You definitely want a glue that sets up hard in
hot weather.
If not, as the temperature increases the glue/bond gets softer/weaker
and
chances of roll off and serious injury increase. The article
listed seven
glues in this order of strongest to weakest tire/rim bond; Vittoria
Mastik'
One, Continental, Wolbar, SM Fast Track, Vittoria Gutta, Pana Cement
and
Clement. I prefer clear glues. That way if you screw
up its very
difficult to tell. With colored glues, if you screw up everyone
knows.
Also for your information I use Pana Cement. It does not provide
the
strongest bond, but it sets up perfectly in all extremes of hot weather
and
it takes one hell of a finger bleeding effort to get the tire off the
rim.
Gluing tubulars to new rims properly should take about 84 hours.
Here's
the process. Test mount the tubular to a dry rim, inflate to
100 psi and
allow to sit 24 hours. This stretches the tire which will make
mounting
easier and also allow you to inspect the tube and tire for defects
(most
"good" tubulars are hand made). After 24 hours remove the tire.
Clean the
rim with acetone, lacquer thinner or alcohol only. Other types
of cleaners
may leave a film on the rim that cannot be seen by the eye and will
decrease tire/rim bond strength. Composite rim owners should
contact the
manufacturer for recommended solvents. Roughing the rim surface
will not
improve the bond strength. Gently scrap the base tape on the
tire with a
straight edge to remove any latex. If you scrap a one inch section
and the
appearance of the base tape does not change, then you probably have
no
latex on the base tape and can stop scrapping. But be sure to
visually
inspect the entire base tape just to be sure.
Inflate your tire off the rim until the base tape rolls outward.
Apply a
uniform layer of glue over the entire base tape area. It is best
to do
several tires at this time. You can store those tires not used
and
anticipate that the adhesive bond will remain strong as long as the
tire
surface is kept clean. Apply a uniform layer of glue across the
entire
width of the tire rim gluing surface. The principle bond
is at the rim
edge; therefore, it is critical for performance to ensure that the
glue
reaches the edges of the rim. Allow both to dry for 24 hours.
Apply an
additional coat after that 24 hour period and allow that 2nd coat to
dry
for 12 hours. Apply a third coat. This is the mounting
coat. With Pana
Cement, once the third coat is applied to the tire and rim mount the
tire
immediately. (One tip I would suggest here is before putting glue on
the
rim is to put black electrical tape on the entire outside edge and
breaking
surfaces. This makes for very easy cleaning after the tire is
put on.
Just peal the tape away and all excess glue comes with it and leaves
behind
a nice, clean breaking surface).
Place the rim vertically on a clean, smooth surface with the valve hole
at
the top of the rim. Place the valve stem through the hole and
ensure that
it is properly aligned-straight through the hole (Another tip…For those
with deep dish rims requiring valve extenders, place a small amount
of
loctite on the tube valve stem threads and then screw the valve extender
on. This will prevent any leaking at that junction once the tire
is glued
on). Grab the tire 8" away from the valve stem in both directions,
pull
outward with a mighty heave and place the section of tire between your
hands on the rim. Slide your hands down another few inches down
the tire,
pull and install this section. Once a full 180 degree section
of the tire
has been mounted, turn the wheel over and place the valve stem section
down
vertically on the ground. This is the point where I have my wife
hold the
section of tire I had just put on the rim with two hands at 0 and 180
degrees. I then grab the tire at the top and turn it so the base
tape is
facing up. At this point I pull up on the tire and roll it onto
the top of
the rim. It's actually very easy with two people.
Once the tire is on the rim, it must be aligned. Inflate the tire
to
about 50 psi so it can be easily "turned" to align. You can either
align
the tire by the tread or by the base tape. Here, I prefer to
align my
tires by the base tape. Higher quality tubulars treads will align
properly. Lower quality tires were not necessarily made straight,
so
perfect alignment may not be possible. Once aligned, inflate
the tire to
100 psi and allow to dry for preferably for 24 hours.
When gluing tubulars to used rims, do not remove the old tire until
you
are ready to begin the gluing process as the old tire keeps the rim
surface
clear of debris which would weaken the new tire joint. You must
find a
weak point in the joint and begin removing the old tire. On my
Zipp 440's,
I use a tire lever so I do not damage the rim surface. On aluminum
rims
you can use a flat head screw driver to make it easier. You may
glue a new
tire over the old glue on the rim unless it is not contaminated or
old, if
there is too much glue on the rim or if the remaining glue covers the
rim
only in spots. If one of these conditions applies to your rim,
remove the
old glue with heavy duty furniture stripper. Apply the stripper
according
to the manufactures recommendations. I always put the stripper
on and let
it sit for 30 to 45 minutes and the old glue then wipes away like butter.
DO NOT wipe the glue along the rim. This causes the old glue
and stripper
to be pushed down into the nipple holes. Wipe across the rim
in small
sections. Once the rim is free of glue, begin the process as
described
above in the article. If you leave the old glue on the
rim, apply at
least one additional coat before installing the tire. To the
tire, apply
at least one coat and let it dry for 24 hours before putting on the
mounting coat.
In concluding, let me state once again everyone has their "best" way
to
mount tubulars. I can honestly say I have mounted and raced on
tubulars
put on in 24 hours. Those instances are far and few between though.
I
always make a 100% effort to follow the procedure written above if
all
possible. 84 hours seems like a long time to wait just to mount
a stupid
tire. It all comes down to how much you value safety. When
it comes to
the safety of the other riders, not to mention the consequences of
roll off
to my wife and my job, I want to be damn sure I'm as safe as I can
possibly
be because I took the time to do things right!