Bicycle brakes are used to slow or completely stop a bicycle and fall into three different categories: rim, drum, and disc. All three types function by applying friction to part of either or both wheels with a static, rider operated braking mechanism. Bicycle brakes are typically applied with cable or rod actuators operated by the rider via handlebar mounted levers or pedal controls. The friction applied to the wheels generally comes courtesy of sets of rubber or composite material pads which are pressed up against the wheel rim, a hub mounted disc, or the inner surface of a hub drum.
The most common, and one of the oldest, braking systems used on a wide range of different bicycle types is the rim brake. This brake variant relies on a set of brake shoes mounted over the wheel on a caliper. When activated, the caliper closes and presses the brake shoes, typically heat resistant rubber blocks, up against the wheel rim. The friction caused by the contact between the shoes and rim bleeds energy off the moving bicycle, thereby slowing and eventually stopping it.
There are a wide range of different caliper designs used on rim bicycle brakes including cantilever, center pull, and side pull designs. The calipers are typically actuated by a Bowden type cable operated by a lever on the handlebars. These brakes are simple to adjust and repair and fairly effective although they do tend to loose efficiency when the rim is wet.
The second commonly used braking system is the drum brake, either as dedicated braking or braking and free wheel types. Operated by rods, cables, or back pedal pressure, these brakes press a set of brake shoes up against the inside of the wheel hub much like the drum brakes on an automobile. Free wheel bicycle brakes are unique drum brake arrangements allowing the rear wheel to "free wheel" while coasting down hills and supplying braking via the pedals. When the rider pedals forward, the hub turns the wheel. When the pedals are kept static, the rear wheel runs free, and when the pedals are pushed back they activate the drum brake. Also known as back pedal brakes, this type of braking system is widely used on the ubiquitous roadster cycles common in Asia and Africa.
The third type of bicycle braking system also obtains its design from automobile brakes. Disc bicycle brakes feature a flat disc attached to the wheel hub which travels through a co-mounted caliper. The caliper features one or more sets of piston actuated brake shoes which may be mechanically or hydraulically operated. When activated, the piston pushes the shoes against the disc, thereby applying braking forces to the wheel. While very effective, these brakes require several modifications to conventional wheel designs which add weight and cost to the bicycle.