https://f30.bimmerpost.com/forums/sh...ht=437m+square
his wheels are 19x9 +29 with 255/35/19. if you used 18x9 +30 with 255/40/18 square, the position of your wheels/tires would be just 1mm further in than his, basically the same place. it is poking a little bit, but if you like what you see, get 18x9 +30 with 255/40/18 square.
18x9, +40 square with 255/40/18 should fit as well however the inside of the front wheel/tire will be close to the spring perch and strut and may even touch depending on the tire
https://f30.bimmerpost.com/forums/sh...lo08816&page=2
you could also do +30 front, +40 rear, but then no rotation front to back
18x8 245/40/18 with either +30 or +40 offset fits without issue. obviously, the +40 will be 10mm more tucked than +30.