The Racing brake disc is two-part and comprises an aluminum center bell and the floating steel rotor. The aluminum center bell reduces the un-sprung mass and improves heat dispersion. The steel rotor is even more robust than the standard brake disc and, thanks to the slotted design, ensures even more effective heat dispersion. Fits front axles on all models. The rear axle Racing brake caliper (X0871950044) is required for fitting on rear axle. Not approved for use on public roads.