Ultimate rotors will stop your BMW faster, straighter and safer. Hard braking generates heat. This heat breaks down the brake pad material, developing a thin layer of gases between the pad and the rotor. This causes the pad to essentially float over the surface of the rotor (like the puck in an air hockey game) instead of grabbing it. Cutting slots and drilling the rotors gives those gases a way to escape or vent. This eliminates brake pad float, minimizes fading and stops your BMW sooner. And they look great behind open-spoke wheels. Install them with the slots and cross-drilling sweeping backward for exceptional braking. Install them with the pattern sweeping forward ( for extra bite on the pads ) to achieve the ultimate in stopping power. Wear indicators on the rotors tell you when the rotors need replacing. Sold in pairs.