Description Reviews SP Performance Slotted Front Rotors for Gen 2 Cooper R55, R56, R57, R58, and R59 models. These high quality slotted rotors are provided with a gray ZRC coating. It provides long-lasting protection against corrosion in the most hostile salt-water environments. After being applied, ZRC provides the highest level of galvanic protection. The film of ZRC is conductive. After the coating heats up during use, it bonds permanently to the metal surface. It will not allow the metal to corrode, even when the surface is scratched. Note: Rotors sold in a set, with 1 left and 1 right.