Disc Brake System Components
The disc brake system converts kinetic energy (vehicle motion) to thermal energy (heat) through hydraulically forced friction. The four major components are: the rotor (disc), the caliper, the brake pads, and the hydraulic circuit. The rotor is a cast-iron or composite disc bolted to the wheel hub; it spins with the wheel and serves as the friction surface. Most modern rotors are vented (two friction faces separated by cooling fins) to dissipate heat from high-energy braking events. The caliper straddles the rotor like a clamp; hydraulic pressure from the master cylinder forces the caliper's piston(s) to squeeze the pads against the rotor faces. Floating calipers (most common) have pistons on only one side — the caliper slides on greased slide pins to apply equal force to both pads. Fixed calipers (high-performance applications) have opposing pistons on both sides. Brake pads consist of a steel backing plate with a friction material layer bonded to the rotor-contact face. Friction material compounds vary: organic (non-asbestos organic, NAO) pads are quiet but dust heavily and wear faster; semi-metallic pads contain steel fibers for durability and heat resistance but generate more rotor wear; ceramic pads are the premium choice for low dust, consistent cold-weather performance, and rotor-friendly formulation. Wear indicator tabs on the inner pad's steel backing plate contact the rotor when pad material reaches minimum thickness (~2mm), generating the characteristic metal-on-metal squeal warning.