well im running 18x9.5 +15 with 245/35/18 up fronts (clears my z brakes and my fender really well) and my rears im running 18x10.5 +18 with 265/36/18. I needed to roll my rear fenders slightly but came out sweet....
to get an understanding of this...check out
www.rimtuck.com...it will show you the offsets on each car and wheels.