I have a 2001 SLK 320 with the original 16 inch wheels. I want to upgrade to a larger wheel--either 17 or 18 inches. I have seen pictures of SLKs with what appears to be 18 inch rims, but message traffic on the forum seem to indicate there are problems with mounting larger rims (offsets, rubbing, etc.) What should I know before shopping for larger rims?[B)]