FWIW I run G-Loc R18 front and R12 rear. I have no issue with ABS or bias. I do have the racing ABS module though. Front and rear pads wore exactly the same, so i think on the smaller rotor, the rear would have gotten hotter and worn faster. I use DBA 4000 1 piece rotors that are slotted. I did the GT500 brackets and DBA rotors that are 13.8 inch. I have not had one bit of noticeable extra rear bias under very heavy braking.