Pads & Shoes

The disc brake is a device for slowing or stopping the rotation of a wheel. A braking disc (or rotor in US English), usually made of cast iron, is connected to the wheel or the axle. more...

To stop the wheel, the braking pads (mounted in a device called a brake caliper) are squeezed mechanically or hydraulically against the disc on both sides. Friction causes the disc and attached wheel to slow or stop.

History

Experiments with disc-style brakes began in England in the 1890s; the first ever automobile disc brakes were patented by Frederick William Lanchester in his Birmingham factory in 1902, though it took another half century for his innovation to be widely adopted. The first designs resembling modern disc brakes began to appear in Britain in the late 1940s and early 1950s. They offered much greater stopping performance than comparable drum brakes, including much greater resistance to "brake fade" (caused by the overheating of brake components), and were unaffected by immersion (drum brakes were ineffective for some time after a water crossing, an important factor in off-road vehicles). Disc brakes are also more reliable than drum brakes due to the simplicity of their mechanics, the low number of parts compared to the drum brake, and ease of adjustment. Unlike a drum brake, the disc brake has no self-servo effect and the braking force is always proportional to the pedal force being applied by the driver.

Disc brakes were most popular on sports cars when they were first introduced, since these vehicles are more demanding about brake performance. Many early implementations located the brake disc inboard, near the differential, but most discs today are located inside the wheels. (An inboard location reduces the unsprung weight and eliminates a source of heat transfer to the tires, important in Formula One racing.) Discs have now become standard in most passenger vehicles, though some retain the use of drum brakes on the rear wheels to keep costs and weight down as well as to simplify the provisions for a parking brake or emergency brake. As the front brakes perform most of the braking effort, this can be a reasonable compromise.

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