Brake Pads

Bicycle V Brake Pad Adjustment

Brake pads can be adjusted in 5 different directions:

• Height  - This is the most critical adjustment. The pad should contact the rim fully, but not overlap it. If the pad is set too high, it will rub on the tyre, destroying it very quickly. If the brake pad is set too low, it can "dive" under the rim and get caught in the spokes, leading to dangerous wheel lockup. On mountain bikes with narrow rims and big bulgy tyres, it may be quite difficult to get a good vertical adjustment--the shoe may clear the tire when the brake is engaged, but it may rub on the sidewall of the tire in its rest position. As the brake pad material wears down, the pad hits lower and lower on the rim, increasing the risk of "diving" into the spokes, so periodic checking is in order.

• Roll angle - The roll angle should be set so that the brake pad hits the rim squarely, both the top and bottom of the pad should meet the rim. If this is not set perfectly, normal pad wear will eventually even it out, but braking will be less effective until the pad has worn in.

• Pitch angle - The pitch angle should be set so that the pad follows the curvature of the rim as closely as possible.

• Yaw angle ("toe in") - The pad can be set so that the front edge contacts the rim slightly before the rear edge. This is commonly called "toe in." If this is not set perfectly, normal pad wear will eventually even it out, but braking will be less effective, and the brakes may squeal until the pad has worn in. Some brakes, however, use asymmetrical shoes (longer end faces the rear) that are designed to be set with no toe in.

• Extension - Extension is the adjustment of the distance from the pad braking surface to the cantilever arm. Direct pull cantis aren't very critical about this, as long as there's a reasonable distance betwen the tops of the arms.

Squealing & Squeaking

Squealing brakes is a common problem, and there's no one simple solution to it.

It's caused by the friction of the brakes against the rim flexing the brake arms, which then slip back, grab, slip back, grab, etc. This process happens at such high speed that it often causes an audible vibration.

All brakes do this, but with luck the pitch (frequency) is too high for human hearing.

This is generally annoying, but not a safety issue. Unlike automotive brakes, bicycle brakes that squeal are usually in good functional condition.

Here are some things to try if your brakes squeal:

* "Toe in" the brake shoes, so that the front edge of the shoe hits the rim slightly before the rear edge.

* Clean the rims with a good, oil-free solvent (citrus, alcohol, something like that.)

* If the pivots of your brakes are adjustable, make sure that you've eliminated as much play as possible without causing them to bind.

* Different brake shoes may help.