The brake discs is a smooth circular steel plate that spins with the road wheels and is used with the brakes to slow the vehicle.
Located behind the wheels the disc is straddled by the brake calipers which contain the brake pad system.
The disc is in a fixed rotation with each wheel, when the brakes are applied the brake pads, on each side of the disc, which are located in the caliper, are forced hydraulically onto the disc which, through friction, slow the rotation of the disc and subsequently the wheels and the vehicle.
Problems with the brake discs can include excessive scoring of the smooth surface, due to the failure to renew brake pads, or corrosion. Removal of the disc requires caliper removal.
Due to the high energy forces, heat, friction and stresses involved with the braking system in the area of the discs and wheels it is of the utmost importance that all components are in good order.