https://f30.bimmerpost.com/forums/sh...&postcount=311
https://f30.bimmerpost.com/forums/sh...&postcount=313
the links above show obzen's F36 rwd 255/40/18 on 9 ET30 at m-sport height. at stock height your x-drive gaps will be bigger. if you go with 245/40/18 increase gaps 3.8 mm.
with either size(
but moreso with 245) you'll want to get lowered to reduce the gap and inherently tuck the upper shoulder of the tires slightly more. i suggest Eibach Pro-Kit E10-20-031-05-22 with F80 bumpstops over Koni SA dampers and rest of the bits comprising the strut/shock assembly.
sorry to have opened "another can of worms", lol.