the reason for no caps is that when the wheels heat up, air pressure builds underneath them and they can literally pop off. my friend has RE30's with nice caps and after doing some laps at VIR he pulled into the pits and when he stopped he heard "pop..........pop pop.......... pop" and they had all popped out. when racing, what the wheels are designed for, you don't want caps, therefore they didn't even try to make them to accept caps

Your friend is lucky! During a track day, I saw the aftermath of a center cap coming of wheel and hit the front lip of a car running behind it, taking a huge chunk out of the lip. Center caps should never be run on the track!

This sort of mod should only be used for cosmetics, never when on the track.

yea he was lucky to have it happen there. had he stayed out another lap i'm sure they would have been long gone/trashed