Also known as a floating disc assembly, two-piece brake rotors consist of an outer ring (this is the part the brake pads contact) and a center piece (hub) that bolts to the car. The outer ring and hub are bolted together forming a functional rotor. The outer ring is made of cast iron and the hub is made of aluminum which means the heat from the pads contacting the outer ring doesn't transfer to the hub, keeping heat away from the wheel bearings. Usually, 2 piece rotors are lighter as well. Zero In Racing offers 2 piece rotors from DBA and Wilwood.