I am helping my friend looking at 18" wheels for the 2008 xD. We were wondering what is the correct tire size for the rims with no rub. The rims he looking at vary from 7"-8" wide.

depending on the offset you go with.

I have 18x7.5 35 offset and they rub.

18x7.5 45 offset seem to do fine, some even have 5mm spacers on them to take em out to 40 offset with little to no problems.