Spoon calipers - OEM wheels clear with no spacers, 15x6.5" ET42 regamaster EVO require 6mm spacers
Brembo touring car race calipers with 300x28mm 2 piece discs - 15x7 ET35 buddyclub P1 racing SF require 6mm spacers (the above regas would have needed 25mm.........)
any SERIOUS brakes such as race brembos / AP's will need wheels with big clearance, for me i have to have the wheel weights placed further in board to allow the caliper to clear the baskets of the wheels also
Anything over 3mm spacers you will need ARP extended studs, also never ever ever run aluminium wheel nuts, this is just common sense though, steel wheel nuts are the best