with your original planned rims use 225/45/18(
somewhat stretched) on 18x8.5 ET30 front + 255/40/18(
lightly stretched) on 18x9.5 ET35 rear OR
do 255/40/18 lightly stretched on 18x9.5 ET35 square, such as in the link below...
https://f30.bimmerpost.com/forums/sh...&postcount=460