Here is my winter set up, 275/315-20" on the factory 20" wheels the tires are all season continental DWS that are surprisingly good in deep snow and on ice. The picture is on a frozen lake.

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X5M Eisenmann exhaust, de-Catted down pipes, 22" HRE wheels, ECUProgram stage II (700hp) tune
X5 35d Tuned and Lowered