Mechanical Advantage
stop!
Maintaining your bike’s brakes
by Jan Heine
Your bicycle’s brakes must be maintained in good working order to
perform optimally. Poorly maintained brakes can be dangerous not
only because they compromise your ability to stop, but also because
they can lead to tire blowouts. Whether you have ridden your bike through the
rain and grit of the winter months or you’re taking it out of hibernation, it’s a good
idea to check your braking system every spring. This article explains how to check
your rim brakes. If your bike uses disc
brakes and if you’re not sure how to
check them, have your brakes inspected
by a qualified bicycle mechanic.
Start the inspection by cleaning the
bike thoroughly, especially in the often
forgotten areas of the brake pads and rim
sidewalls. This gets rid of the grime that
accumulates there and makes the task of
inspecting the brakes much more pleasant.
Check Rim Wear
Your brakes work by clamping the
rim. The resulting friction converts
kinetic energy into heat. This friction
causes the brake pads to wear out, but
the rim also becomes abraded. On clincher rims (found on almost every modern
bike), the rim is pressurized by the tire
and tube. If the rim’s sidewalls get too
thin, they can fracture suddenly, resulting in a tire blowout.
Many modern rims have a line scribed
into their sidewalls. That line is a wear
indicator, and when it disappears, it is
time to replace the rim. On rims without a
wear indicator, it is difficult to measure the
remaining sidewall thickness because of
the bead hook that keeps the tire in place.
As a rule, if you have replaced your
brake pads on a wheel twice, the rim is
probably getting thin. You can use calipers to check whether the rim sidewalls
are still parallel. With the tire inflated
to maximum pressure, see if the walls
are starting to bow outward at the outer
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A DV E N T U R E C Y C L I S T M AY 2 0 1 2 Are there rocks or other debris embedded in the pads? If so, remove the debris
before it ruins your rim. Does the pad
surface look dark and/or shiny even
after you have cleaned them? Brake pads
can “glaze over,” which reduces their
effectiveness. Remove the pad and use a
coarse file to expose fresh rubber.
Figure 1. New (left) vs. worn (right) rims:
After a few seasons of braking, the rim sidewalls have been abraded to half their original thickness, from 1.6 mm to 0.8 mm.
edge of the rim. If they are, the rim
should be replaced immediately. The
same thing applies if the rim shows striations or has been scored by sharp rocks
embedded in the brake pads.
Check Brake-Pad Wear
After you have ascertained that your
rim is still in fine shape, check the brake
pads. If your pads slip into separate
holders, it is easy to see how much pad
material you have left. If your pads have
mounting studs that are molded directly
into the rubber pad material, don’t be
tempted to get that last bit of use out of
them. Inside the rubber is a steel stiffener, and if that gets exposed, it will score
and ruin your rim. Usually, these pads
have a step that shows how far you can
use them. Brake pads are not that expensive. When in doubt, replace them.
If your pads have a lot of material left,
check the surface that touches the rim.
A DV E N T U R E C Y C L I N G . O R G
Check Brake-Pad Alignment
Most bicycle brakes move the brake
pads on an arc-shaped path. As the pads
wear, they no longer touch the rim in the
correct spot. When brakes have a pivot
below the pad (cantilever or V-brakes),
the pad moves lower on the rim as it
wears. This can result in the pad diving
under the rim when you brake very hard
in an emergency, resulting in a total loss
of brake power.
When brakes have a pivot above the
pad (dual pivots, side-pulls, center-pulls),
the pad hits the tire as it wears. This can
cause the pad to rub through the tire,
resulting in a blowout.
Check pad alignment by looking at
the pad. The surface that touches the rim
should be smooth. If your pad is showing a ridge at one edge, it means that it
is not aligned with the rim. Before you
realign the pad, file off the ridge (or use
a new pad).
Also squeeze the brake lever hard and
see where the pads touch the rim. The
pads should be centered on the rim, and
no part of the pad should extend beyond
Figure 2. As the brake pads wear, they no longer touch the rim at the same spot. For
each brake, the unworn pad is shown on the left, the worn pad on the right. On cantilever and V-brakes, the pad can dive underneath the rim. On dual pivot, side-pull or
center-pull brakes, the pad can abrade the tire and cause a blowout.
the rim surface. If your rim is narrow
and your brake pads are too wide, get
narrower pads!
While you are checking your brakepad alignment, check that your pads are
“toed-in” correctly. Squeeze the brake
lever lightly until the pads barely touch
the rim. Ideally, the leading edge of the
pad should touch the rim first. If the
trailing edge touches the rim first, your
brakes will squeal and your braking
power will not be optimal. Adjusting
brake pad toe-in can be tricky on some
brakes. If you cannot get it right, have a
qualified mechanic do it for you.
Check Brake Cables and Levers
Visually inspect the brake cables.
Quality brake cables usually do not wear
out, but if the cable is frayed or has broken strands, replace it. If the housing
has kinks, replace it as well. Pull on the
levers. They should be easy and smooth
to pull until the brake pads hit the rim.
If you feel resistance, you probably need
new cables and housing.
To check the brake-lever travel,
squeeze the brake levers very hard.
They should not bottom out against
the handlebars. If a lever does touch
the handlebars, release it and check
the distance between rim and pads.
If this distance is larger than 2 mm,
your pads should be moved closer to
the rim to make up for the wear of the
pads. (If the pads already are close to
the rim, your brake levers and brakes
may be mismatched. Ask your bike
shop about brake levers with more
cable pull.)
Brake levers, brakes, or both are usually equipped with a barrel adjuster. On
most models, you turn the entire adjuster
to screw it out. This elongates the effec-
tive length of the cable housing, which
in turn shortens the effective length of
the cable, bringing the pads closer to the
rim. The adjuster also features a nut that
you screw down onto the body of the
lever or brake to lock in the adjustment.
If the adjuster is screwed out so far that
only a few threads are engaged, screw
it all the way back in and shorten the
brake cable itself at its attachment point
to the brake.
Brake levers also rarely wear out, but
if they are obviously bent or don’t move
smoothly, replace them.
Play It Safe!
If you have any doubt about your
brakes, take the bike to a qualified
mechanic who can inspect it for you.
Your braking system is a crucial element
in the safety of your bike.
After you have inspected your brakes,
you can go for a ride, confident in your
ability to slow down or stop when you
need to. It’s a great feeling when you
know you can rely on your bike.
Jan Heine is editor of Bicycle Quarterly, a magazine
about the culture, technology, and history of cyclotouring. His blog is at janheine.wordpress.com.
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