That's great thanks.
What if the tyre is wider than the rim, is that ok or not? My 205/45/16s are 8.07 inches wide but if I use a 7J rim, isn't that only 7 inches wide?
Thanks again
rims aren't measured from the very outside of the rim, they are measured from the internal bead i.e where the tyre actually mounts.
http://www.youtube.com/watch?v=B0SLpz3Fs4c