Originally Posted by JHM2K

On the 2002-2004 C32, they used one rotor for left and right applications. Therefore, the vanes point one way on the R/H side of the car, and the opposite on the L/H side. The central cooling vanes are consistent between the two, so it was a cost-savings measure for production.

Neither direction on the rotor surface is superior to the other... the grooves are only there for evacuation of gasses.