The specific function of vehicle brakes can vary significantly according to the type of vehicle and the current technology being used. The most common type of modern vehicle brakes is the disc braking system, which is a hydraulic system that uses pistons that press against a metal disc known as a rotor. Other systems used for vehicle brakes include drum brakes, inboard brakes, and hand brakes; these systems are usually used on automobiles, though they are also commonly used on motorcycles and even bicycles. Bicycles also use rim brakes, which have rubber pads that press against the sidewalls of the rim to stop the bicycle.
Disc brakes are used on most modern automobiles and motorcycles, as well as on some bicycles. Hydraulic systems are most commonly used for vehicle brakes in this case, though cable-actuated disc brakes are available, usually on bicycles. The hydraulic systems are initiated by depressing the brake pedal in an automobile; this action pushes hydraulic fluid — usually some type of oil — through a master cylinder and through the brake lines. The force of the hydraulic fluid then actuates the brake caliper system, which consists of a housing along with moving pistons positioned on either side of a rotating disc known as a rotor. The hydraulic system allows for modulation, or the ability to vary the amount of pressure being applied to the rotor. The vehicle can be slowed smoothly, or stopped suddenly.
Drum brakes very often work very similarly to disc brakes as far as the hydraulic system is concerned. The difference lies in the brake actuation at the wheel. Instead of using a disc rotor, the drum brake uses a metal drum within which the brake shoes are mounted. The brake shoes press outward against the inside of the drum; they are pushed outward by a wheel cylinder that is connected to the end of the brake line. When the fluid presses into the wheel cylinder, two arms push outward on either side of the cylinder, activating the brake shoes.
Inboard vehicle brakes work similarly to disc brakes, but the location of the brake caliper and rotor is changed to be mounted on the axle rather than close to the wheels. This is done to improve handling in most cases; this system is far rarer than other brake systems. Cable actuated hand vehicle brakes are commonly known as emergency brakes, or e-brakes. These brakes are activated by a lever which pulls a length of cable. The cable is mounted to the rear brakes of an automobile and actuate the brake pads in an emergency situation. This braking system does not allow for much modulation and is used primarily as a parking brake.