The two main types of braking systems used in bicycles today are caliper brakes and cantilever brakes. Both apply pressure on the rim of the wheel to stop the bike and are considered rim brakes. While calipers have been and continue to be the most common brakes found on bikes, the newer cantilevers are stronger and have become more popular in recent years (see Figure 2-9).
Rim brakes work through a system of levers and cables. Cables connect the brake levers (located on the handlebars) to the brake arms that surround the top of the wheels and are secured to the fork in front or seat stay in back. When the levers are flexed by hand, the cables pull, closing the brake arms around the rims. When the levers are released the brakes spring back to their original position.
The section of the brakes, called the brake pad or brake shoe, that comes into contact with the moving rim is usually made of rubber or leather to maximize the friction needed to stop. All other parts of the braking system—arms, cable, and levers—must be rigid and precisely positioned to transfer the relatively light force exerted by hands on brake levers to the high power needed in the brakes for effective braking.
Figure 2-9 BRAKES: CALIPER CENTERPULL (TOP); CALIPER SIDEPULL (CENTER); CANTILEVER (BOTTOM)
Most caliper brakes are sidepull, meaning the cable pulls the two brake arms (one on each side of the rim) from the same side of the wheel. Centerpull calipers, which are somewhat out of date and much less common, pull the brake arms from above the wheel. With centerpulls, the main brake cable forms an inverted Y shape with a second straddle cable, which connects to both brake arms separately on both sides of the wheel. Either method is effective for most bikes, but design considerations make sidepulls work better with thin wheels while centerpulls are more effective with wide tires.
Cantilevers are also centerpull brakes (technically, they're also considered caliper brakes), but they do not function in the same way as calipers. The essential difference between cantilevers and traditional calipers is that with cantilevers the two brake arms are mounted separately and work independently, while with calipers the brake arms work together as a unit. As with centerpull calipers, cantilevers use a straddle cable to divide the brake cable's pull among the two sides.
Originally designed for use on tandem and BMX bikes, the high-power cantilever brakes have become quite common on mountain bikes and some touring bikes as well. Because they offer better stopping power, cantilevers are recommended for bikes that carry heavy loads or make steep descents. Most racers, meanwhile, stick with calipers because they're smaller and more aerodynamic.
Other Brake Types
Older and less sophisticated bikes may use the coaster brake, which works by pressing backward on the pedals. Simply, the backward motion counteracts the forward spin of the rear wheel to slow and stop the bike. Other less common brakes include U-brakes and cam operated brakes, both of which are variations on the caliper and cantilever designs, and hydraulic brakes, which use compressed liquid (usually oil) for stronger braking force.
Drum brakes and disk brakes are entirely different braking systems that use hand-activated cables but work at the wheel hub. Drum brakes use flexed cables to push brake pads against the inside of the hub shell to stop the turning of the wheel. Disk brakes use caliper-style brakes to clamp onto a small disk that turns along with the wheel and is located next to the hub.
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