I'm confused also.

You're putting GM wheels on your X5?

Or are you taking the tires off of GM wheels and having them installed on your existing X5 wheels? If so and as said above, as long as your X5 wheels are within the tire manufacturers recommended wheel width there shouldn't be an issue. All I'll say is that 235mm seems narrow as the recommended winter tire from BMW is 255mm wide.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim