Originally Posted by slicer
BMW actually recommends 235/40/18 in the front and 255/40/18 in the rear (on their winter 18x8, 18x9 wheels). They don't recommend 235/40/18 on the 9.5" rear wheel. That tire is too narrow for a 9.5" wheel.
Where do you get your information from? They are actually 18x8 square (270m) and they recommend 235/40 on their winter wheel. That being said, I have 235 on my OEM (219m) set up right now and it is doing great (stretched but fine) in Germany where we have had significant amounts of snow in the past two weeks. Not sure where you are getting your facts but I linked a few sites to help you out. If you notice, tire rack also recommends 235 square or you may choose the 235/255. Now, the 235 in the rear is better for handling when it comes to driving in the snow being that it allows the wheel to cut into the snow easier than a 255 tire which is wider.