All StopTech Balanced Brake Upgrades are shipped with slotted AeroRotors, however drilled or slotted rotors can be substituted for an additional $50 per rotor. Slotting assists in removing the debris generated between the pad and rotor during braking as well as increasing the "bite" characteristics of the pad/rotor interface. A drilled rotor provides the same benefits and works better in the wet, but is more susceptible to cracking under severe usage, as well as causing greater pad wear. Many customers prefer the look of a drilled rotor, and as long as they will only be used for street and occasional light track use, they will work fine. For more severe applications, where elevated rotor temperatures are expected on a regular basis, StopTech strongly recommends slotted AeroRotors. 332 x 32mm