A vehicle’s disc braking system is made of many parts and the disc brake rotors play an important role. By pressing the brake pedal, the calipers engage and grab the rotors or the brake discs, which causes the wheels to slow and stop. A vehicle's front and back brakes may have different disc brake rotor sizes. Make sure you measure your current ones to get the correct replacement. If you are doing a complete brake replacement, you’ll also need brake pads, lines, and other brake accessories.