StopTech AeroRotor Replacement Kits ARK are designed to replace your vehicle's original factory rotors, while retaining the factory brake calipers. Although the ARK is the same diameter and thickness as the factory rotors, it offers improved cooling, braking, and handling. The directional, floating AeroRotors allow independent expansion of the rotor and hat without "coning," thanks to elongated drive pin holes. ARK components include AeroRotor friction rings with patented internal vane design, pre-assembled to billet aluminum AeroHats with directional stand-offs that optimize cooling airflow. The patented AeroRotor vane design pushes up to 80 percent more air than factory rotors for better cooling and reduced fade on the track. The aircraft-grade aluminum hats and 2-piece AeroRotors are up to 8 pounds lighter than stock rotors, allowing faster acceleration and deceleration, and improved handling. StopTech AeroRotors are available slotted or cross-drilled. These slots or holes allow better dissipation of heat, friction material and debris, assuring that fresh pad material is in contact with the rotor every time the brakes are applied. An optional anti-corrosion, zinc finish is available for customers in cold climates, where salt and chemicals are used to melt snow and ice. The zinc coating also benefits customers who prefer no visible surface rust on the vanes and outer circumference of the rotors. StopTech AeroRotors are 100 percent made in the USA. Reduced Unsprung and Rotational Mass. Improved Thermal Capabilities. Optimized Heat Dissipation. Designed to Work with OE Calipers 2012 - 2015 BMW 335i, 2013 - 2013 BMW 328i xDrive, 2013 - 2015 BMW 335i xDrive, 2013 - 2015 BMW ActiveHybrid 3, 2014 - 2015 BMW 335i GT xDrive, 2014 - 2015 BMW 435i, 2014 - 2015 BMW 435i xDrive, 2015 - 2015 BMW 435i Gran Coupe, 2015 - 2015 BMW 435i xDrive Gran Coupe