In the days of asbestos pads, says Dong, there was a gas boundary layer that appeared at the interface area of hte pad and rotor. Although that gas boundary still occurs, it is much less of a problem with modern friction materials. Slots are more then adequate to carry that gass away.

Years ago, that gas boundary , allong with reducing weight, led to the popularity of drilled rotors. However, in the intervening period, the myth has persisted that cooling is the main reason for drilling rotors. Any one that tells you thad drilling makes the disc run cooler, says Dong, "is smoking crack." Although there is a belief among some that drilling can have a slight effect on cooling by drawing addinional air in to the vanes, even those that subscribe to that theory say drilled rotors are more of a liability than a benifit.

"Drilled holdes tend to be stress risers and they tend to be a stress concentrator," says Ruiz. "therfore a driled rotor will tend to have a shorter life then an undrilled rotor. The contribution a drilled rotor makde to the system, reducing gas and debris, can be accomplished with a slot." Not only will rotor life be shorter, but also an on-track failure is likely to be more catastophic than with a non-drilled disc.