Check the bottom half of
this page. That shows my winter set up which is OEM rims with 255/55/18's. I use 30MM HR spacers on the rears, none on the front. My fender flares make the small rims look worse than on an X5 without flares. There are quite a few guys here running that same spacer.
HR Website. Check ebay or google, you can buy these spacers all over.