Brake pad

[1] When the brakes are hydraulically applied, the caliper clamps or squeezes the two pads together onto the spinning rotor to slow and stop the vehicle.

When a brake pad heats up due to contact with the rotor, it transfers small amounts of its friction material onto the disc, leaving a dull grey coating on it.

Racing calipers, however, can utilize up to six pads, with varying frictional properties in a staggered pattern for optimum performance.

Depending on the properties of the material, the weight of the vehicle and the speeds it is driven at, disc wear rates may vary.

A common technique is manufacturing a small central groove whose eventual disappearance by wear indicates the end of a pad's service life.

Other methods include placing a thin strip of soft metal in a groove, such that when exposed (due to wear) the brakes squeal audibly.

[2] However, due to high cost and inefficiencies compared to drum brakes they were not commonly implemented until after World War II.

The performance difference was most noticeably exhibited in 1953 when a Jaguar outfitted with brake pads won the 24 Hours of Le Mans Grand Prix of Endurance race.

[7] Asbestos was added as a common ingredient to brake pads post-WWI, as car speeds began to increase, because research showed that its properties allowed it to absorb the heat (which can reach 500 °F) while still providing the friction necessary to stop a vehicle.

Asbestos brake pads have largely been replaced by non-asbestos organic (NAO) materials in first world countries.

[9] Today, brake pad materials are classified into one of four principal categories, as follows: Phenol formaldehyde resin is frequently used as a binding agent.

FMSI's mission is to, "Maintain and enhance this standardized part numbering system for all on highway vehicles in use in North America.