If it's only occasional and you care about it working in warm conditions and in the mountains, I'd get another set of wheels (17 or 18). You can get a set of Style 57 17"ers with Michelin MXVs for less than $400, and it's worth it for the piece of mind. It also lets you get very aggressive with the tires you put on your 20s. Just my two cents.

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2002 X5 3.0i