For 513M tire size combo to use for xdrive:
1) 235/45/18(26.3") & 265/40/18(26.3"), 235 is a bit stretched on the 9" up front. taller sidewall helps reduce wheel gap.
2) 245/40/18(25.7") & 275/35/18(25.6"), 0.4% looks like this...
https://f30.bimmerpost.com/forums/sh....php?t=1445526
3) 255/40/18(26") & 285/35/18(25.9") 0.4%, "got beef"?
.