In the car hub installed two semicircle-type brake pads, using "lever principle" to push brake pads to make the brake pads and drum in contact with the friction.
The drum brakes have been used in the car over the past First century's history, but due to its reliability and strong braking force, the drum brakes are now still configured on many models (more used in rear wheels). The drum brake is by hydraulic pressure will be installed in the brake drum to push outward, so that the brake pads with the wheels of rotation of the brake drum within the friction, and the effect of braking.
The inner surface of the drum brake brake drum is the position of braking torque. In the case of obtaining the same brake torque, the drum brake brake drum can be a lot smaller than the disc brakes. Therefore, heavy-duty vehicles for the acquisition of a powerful braking force, only in the ring of limited space in the drum brakes.