Hello I too am looking to upgrade to 20" staggered wheels. Research I've done turns out to utilize as close as possible to stock diameter tire circumference. On my vehicle, it is 27.6, which will not effect the speedometer or cause issues with transfer gear case. I found that Chevy Camaro SS V1160 Staggered wheels are plentyfull and reasonable. Your going to have to look for tires that meet your stock diameter circumference for your model X3. They vary from 17, to 18 which are standard on my model or the option 19s. Keep me posted.