Sitting in my local BMW dealer having the winter wheels removed and swapped with my summers. My rear winter setup are 265/40 -20 on 11" X6M reps and while they tuck a little bit unless you know whta you are looking for they are still very beefy.

The 20" have performed flawlessly for both my wife and I, so no regrets. I am glad I got staggered wheel sizes (9.5"/10.5" on wife and 10"/11" on mine) but that does preclude me from rotating them. I think the look is better than having 9.5" 275s in the rear with flares...and the benefit of the square setup from a deep snow/ice handling department outweights getting the staggered tires to match.

My 2 cents,
Mike

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PCD 12/3/10: 2011 X5 50i/Alpine White/Cinnamon/Bamboo: M Sport, Tech 20" 333, Cold Weather, Premium, Prem Sound, Rear Climate, rear heated seats, HUD, CA,
Wifey's ride: 2011 X5 35i SA Vermillion Red/Tobacco/Walnut Tech 20" 214, Cold, Prem Sound, rear climate, CA