Brake Toe-In: Define "Front"?!!!
sggo...@my-deja.com
Brake toe-in requires that the "front" of the brake pad touch before
the back. I thought this meant that the "leading edge" of the pad -
closest to the back of the bike, from where the rim is approaching on
its way up and around - was the side that touched first. But some bike
repair books are worded such that one might assume that "front" means
the front of the BIKE.
Does the arrow on the pad refer to the direction of rim travel or the
direction from which the rim is approaching...like the wind?
I went and installed new pads with my bike upside down, and managed to
accidentally install the front pads with the trailing edge touching
first. They didn't squeak - but the back pads, leading-edge first,
squeak. This is the exact opposite of what I thought would happen!
Anybody care to define "front" regarding toe-in? None of my bike books
make this perfectly clear....
Thanks
Steve Goodridge (who should know better....)
Sent via Deja.com http://www.deja.com/
Before you buy.
Mel Erickson
gradually make contact with the rim from the front to the rear as more
force is applied. The forward most end of the pad should touch first
(both front and rear brakes). The reason your rear brake squeals is
that the rear of the pad touchs first and grabs, flexes the brake
caliper and sets up an oscillation or shudder in the pad/brake caliper
causing the squeal. This can be demonstrated on the basketball court.
When a basketball player makes a sudden change in direction and the toe
of his shoe comes in contact with the floor first you often here a
squeak. If the same players heel were to come in contact first you
would not here the squeak.
Depending on the amount of toe-in and flex in the caliper/frame, this
squeal may or may not go away when more force is applied. I believe
the arrow should coincide with the direction the wheel is spinning.
--
Mel Erickson
yeti-man
Think of the toed
in pads making an arrow ^ in the direction the bike (or the rim)
travels. The arrows marked on the pads should also point the
direction the bike (or the rim) travels.
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Stanley Goldstein
> Front means front. Er, the front of the bike.
> Think of the toed
> in pads making an arrow ^ in the direction the bike (or the rim)
> travels. The arrows marked on the pads should also point the
> direction the bike (or the rim) travels.
After a good bit of pad wear, I've reversed them so the arrows point
backwards and haven't been able to discern any difference in their
functioning. This is with Shimano 105/Ultegra pads and Koolstops.
Stan Goldstein
gol...@u.washington.edu
sggo...@my-deja.com
> Front means front. Er, the front of the bike.
Thanks to those who replied. This definition of front for proper toe-in
makes sense given the squeal I hear.
Having the pad edge closest to the front of the bike touch the rim
first seems to ensure that any flex in the brake pad and caliper caused
by drag forces will push the pads flat against the rim, rather than
working to rotate them away from the rim.
Toeing the other way seems to increase the concentration of force on
the touching edge rather than distributing it across the pad.
Shame on me for forgetting the basics....
Steve
Jobst Brandt
Brake Squeal
Most brakes on cars, motorcycles, and bicycles squeal at one time or
another, because they involve stick-slip friction, something that
should occur at frequencies above the audible range. Squeal is not
only annoying, it decreases brake efficiency, especially in the lower
frequencies where the slip part exceeds the stick part of friction.
Brake noise requires elastic motion (vibration) to occur on a moving
brake surface with a component in stop-start motion. Bicycles in
particular, not having power brakes, require a high coefficient of
friction and therefore use brake material that is soft and flexible
enough to achieve good contact on relatively rough rims. Bicycle
brakes generally have a mechanical advantage between 4:1 and 6:1, as
described under "Brakes from Skid Pads to V-brakes." That's not much
compared to motorcycles that have hydraulic disk brakes and almost no
pad clearance to take up.
Soft brake pads and flexible light weight calipers invite squeal and
chatter, chatter being the mechanically more detrimental version of
stick-slip behavior. Brake chatter is caused by gummy residue on the
rim together with excessively flexible (skimpy dimensioned) brake
calipers. Rims can be cleaned but flexible brakes can only be fixed
by using better brakes. If the rim becomes gummy again after
cleaning, then either the rims are being contaminated by something
like riding through tar weed or the pads are no good. My solution for
pad quality is Kool-Stop salmon red pads.
Squealing brakes, the more common problem, involves mainly the brake
pad that generates caterpillar like surface waves. The usual advice
is to bend the brake calipers to make the trailing edge of the pad
(with respect to rim motion) contact first (the forward end of the
front brake pad). This is not entirely without merit because this is
the natural state of a used, non squealing brake. Elasticity of the
caliper, however small, allows the pad to follow the rim and rotate
forward about the caliper arm, wearing the heel of the pad more than
the nose, causing toe-in. Toe-in is preferred because a pad that
makes full contact as it first touches the rim will rotate slightly
from frictional drag, reducing contact... and drag, which allows it to
snap back and repeat the action. This causes surface waves in the
pad, especially when it is new and thick. For this reason, some pads
are made with thin friction material to reduce elasticity.
If the pad contacts the rim, trailing end first, it achieves full
contact stably as pressure and frictional drag increase. However, the
brake may squeal anyway. This can occur with new rims or one with wax
or oil, or from other contaminants like those from riding over a moist
lawn. Machined rims have machining grooves, a roughness that reduces
squeal tendencies so they don't have to be "broken in". Some new pads
also may have a glossy skin that should be removed either by sand paper
or use. Many types of residue can increase stiction (stick-slip) that
is easily removed by abrasive scrubbing. This can be done by braking
at moderate speed with household cleanser on a moist rim, followed by
a water bottle squirt rinse (while still braking). This effect is
more easily and conveniently achieved by riding through a long mud
puddle while braking. Better yet, descend a mountain road in the rain
where there is usually plenty of fine grit and where rain supplies the
rinse.
Avoid bending brake calipers. This is "cold setting" in its worst
form. Aluminum in such cross sections doesn't bend far without
structural damage. Besides, this remedy could lead to more bending
with each occurrence of squeal that is better abated by other means.
Jobst Brandt <jbr...@hpl.hp.com>
Lawrence Fieman
about Kool Stop salmon red pads..
"Jobst Brandt" <jbr...@hpl.hp.com> wrote in message
news:8kfm09$5kv$1...@hplms2.hpl.hp.com...
Steve Palincsar
>
> On Tue, 11 Jul 2000, yeti-man wrote:
>
> > Front means front. Er, the front of the bike.
> > in pads making an arrow ^ in the direction the bike (or the rim)
> > travels. The arrows marked on the pads should also point the
> > direction the bike (or the rim) travels.
>
> After a good bit of pad wear, I've reversed them so the arrows point
> backwards and haven't been able to discern any difference in their
> functioning. This is with Shimano 105/Ultegra pads and Koolstops.
You know, Stan, on some brakes those arrows indicate which end of the
brake shoe has the metal block thingie that keeps the rubber from
sliding right out of the brake shoe when you clamp down hard... Boy,
would that ever be embarassing!