offset is on your wheels, tires wouldn't have them. i'm running the 225/40/18 on my Ro_Ja wheels with a 42mm offset. no scrubbage yet.
Well let's see.. if he's getting 18" tires, he's probably going to have to mount them on something, and since the stock wheels are smaller than 18", odds are probably pretty good that he's going to be buying some rims, wouldn't you say?