24s are way too big for an x5. With that 25 series side wall, your just asking for trouble. I'm not even sure how safe that could be. I would go largest 22, but I think a nice 20 with a small bit of lowering looks great. Save the 24s for the bigger SUVs. I don't think it looks good when the overall height of the vehicle is raised just to accomodate the wheels. Plus big wagon wheels really slow your car down in every aspect.

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2007 Jeep SRT-8 (going to be supercharged)
2007 Trailblazer SS
2003 X5 4.6is ESS supercharged
2004 Silverado SS supercharged
2005 Escalade supercharged
2003 Corvette ZO6 supercharged
1999 Mercedes S600