Brake pads are a component of disc brakes used in automotive and other applications. Brake pads are steel backing plates with friction material bound to the surface that faces the disc brake rotor.
Brake pads convert the kinetic energy of the vehicle to thermal energy through friction. Two brake pads are contained in the brake caliper, with their friction surfaces facing the rotor. When the brakes are hydraulically applied, the caliper clamps or squeezes the two pads together onto the spinning rotor to slow/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. The brake pad and disc (both now having the friction material), then "stick" to each other, providing the friction that stops the vehicle.
Disc brake advantages
Disc brakes offer better stopping performance as compared to drum brakes. They provide better resistance to "brake fade" caused by the overheating of brake pads, and are also able to recover quickly from immersion (wet brakes are less effective). Unlike a drum brake, the disc brake has no self-servo effect—the braking force is always proportional to the pressure applied on the braking pedal lever. However many disc brake systems have servo assistance ("Brake Booster") to reduce the driver's pedal effort.
There are numerous types of brake pads, depending on the intended use of the vehicle, from very soft and aggressive (such as racing applications) to harder, more durable and less aggressive compounds. Most vehicle manufacturers recommend a specific kind of brake pad for their vehicle, but compounds can be changed (by either buying a different make of pad or upgrading to a performance pad in a manufacturer's range) according to personal tastes and driving styles. Care must always be taken when buying non-standard brake pads as the operating temperature ranges may vary, such as performance pads not braking efficiently when cold or standard pads fading under hard driving. In cars that suffer from excessive brake fade, the problem can be minimized by installing better quality and more aggressive brake pads.