I think the custom magnesium wheel hubs and adapter plates is what makes the clearance for the AP calipers under Fuchs wheels. I can fit 15X7 fuchs as well as 15X6 fuchs under my calipers and also 15X9 ronals. A spacer will work, but the rally cars did not use spacers. http://www.bufkinengineering.com/testfit.htm James