The primary brake shoe is the brake shoe in a set which initiates the self-energizing action of braking. A brake shoe is a carrier to which the brake lining is attached, used to force the lining in contact with the brake drum or rotor. When brakes are applied, the brake shoes or friction pads are forced into contact with the brake drums or rotors to slow the rotation of the wheels. The friction between the tires and the road surface then slows the speed of the vehicle.