The brake assembly components at the wheels of a vehicle are generally called the foundation components because they form the basis on which the rest of the system is built. Foundation components are the mechanical parts contained in or around the wheels that are operated by the air brake system. An air brake system can be designed to work with several designs of foundation brake subsystems — even on the same vehicle.

There are three types of foundation brake systems — ‘S’ cam brakes, disc brakes and wedge brakes.