The rust you are seeing is normal for any rotor and is in no way a safety or durability concern.
The factory Viper rotors are coated with a silver finish called Dacrament (sic?). We have tried to source this coating, but it is cost prohibitive for our volumes compared to what an OE would process. The alternative is Zinc or Cadmium (Cad) plating. The Zinc has not shown itself to be a durable finish and we have felt it is not worth the effort. The Cadmium plating is much more durable, but has it's own issues. First, the Cadmium plating takes several miles of easy driving with very light braking to wear the coating from the face of the rotor where the pads touch. This is unacceptable in a race environment as a new set of rotors is taken directly onto the track. If not removed in a controlled manner, the Cad plating will actually ball up and imbed itself into the brake pads. Secondly, if over heated, the Cad plating will burn off and actually become somewhat caustic, causing even more aggressive corrosion.
We do offer Cad on our 1-piece direct replacement Viper AeroRotors. We do not recommend it for going directly onto the track, but do feel it is valuable for the typical street only or limited track enthusiast. If you have time to bed-in the system before going onto the track, we feel it is a worthwhile upgrade. The hat section of the 1-piece rotor is very visible (same as the black aluminum hat on the 2-piece) and the plating protects that area very well from corrosion. If overheated, the heat effected zone will adversely affect the plating on the outer diameter of the rotor and the area of the rotor face close to the hat; the same area as the small band of rust around the aluminum hat. It typically will not damage the finish very far onto the hat as the temperatures drop of quickly away from the pads.
I hope this explains what you are seeing. Please feel free to contact me if you have any other questions-
Matt Weiss
StopTech
