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Brakes |
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Four principal braking systems are used on bicycles: coaster, caliper, disc, and drum brakes. Coaster brakes, which are mounted inside the hub of the rear wheel, are usually found only on single-speed utility bicycles or on children’s bicycles (most children do not have hands big or strong enough to squeeze brake levers). Coaster brakes are operated by rotating the foot pedals backward half a revolution until they lock; this expands a mechanism inside the hub that creates friction on an internal brake sleeve. Caliper brakes are almost universal on multigeared road, BMX, and utility bicycles. They consist of a pair of arms that are pivoted together and fitted with brake pads. These arms close onto the metal wheel rims in a scissor-like motion. They are controlled by hand levers mounted on the handlebars that connect to the arms by way of cables. Caliper brakes are available with either side-pull or center-pull cables. Side-pull brakes are frequently used in road racing because their braking force is easily feathered (adjusted minutely). Center-pull brakes are sometimes found on recreational and light touring bicycles; their braking leverage is greater and they can be designed for the larger clearances required for wider tires and rims. Cantilever, cam, and U brakes—always of a center-pull design—are caliper brakes with exceptionally large brake pads and leveraging mechanisms to increase the amount of braking force delivered. These large, leveraged brakes are found most commonly on mountain, touring, commuter, hybrid, and BMX bicycles, where a premium is placed on retaining braking ability even when the bicycle is ridden through dirt, water, or mud. Disc and drum brakes, which operate much like the disc and drum brakes on automobiles, are less common but are sometimes used on tandems, utility bicycles, mountain bicycles, and recumbents that must carry heavy loads. |
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