Bicycles can be the source of a number of noises, and as Jim Langley, former editor of Bicycling Magazine, points out, the description of a noise can be subjective. One person's creak is a clack to someone else. However, Langley points out that whether it's called squealing or squeaking, the most common source of the noise is the brakes, and the cause is the brake pads vibrating against the bicycle rim.
Toed-In Adjustment
In order for bicycle brakes to function quietly, they need to be properly adjusted in a toed-in position. This means that when the brakes are applied, the front of the brake pad touches the wheel rim first, before the rest of the brake pad. If the brake pads are viewed from above, they can be viewed as a person's feet, and the "toed-in" description means that the toes are angled in, toward each other. In this position, the fronts of the brake pads will contact the wheel rim first as the pads are drawn into contact with the rim.
Wear and Cleaning
Worn brake pads may make it difficult to adjust them into the correct toed-in position. If this is the case, replace the pads and make the adjustment with the new pads. If the pads are new or showing little wear, and they are still squeaking, the cause could be a build-up of residue on the rims. The rims should be cleaned with a solvent. Further clean the rim by lightly sanding the surface that comes in contact with the brake pad. Use medium emery cloth. This breaks up any rubber deposits, which may be a source of the squeal.
Nonadjustable Pads
You may find yourself with brake pads that are not adjustable or that your adjustments do not leave the pads in a proper toed-in position. If this is the case, you can use a file on the brake pad to file off a part of the brake pad. Use caution and file only a minimal amount of the pad away as the pad provides the braking action for your bike. File away the backs of the pads so that the front of the pads come into contact with the rims when the brakes are applied.
Considerations
Different types of rims may be more susceptible to squeals. According to Erik West of The Bicycle Workshop, chrome-plated and steel rims are more prone to squeals than other alloys. Brake arms, which hold the pads, that are weak or have too much play can also result in brake pads squealing. These arms should either be tightened or replaced with sturdier arms.
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