OP, You never mentioned if these were going on a coupe or sedan. That being said, $350 for a set of Genesis wheels is a hell of a deal and were it me, I'd jump all over it. Also, be advised that the genesis wheels have an offset between +30 an +35. Its fairly aggressive for a sedan but can be pulled off nicely with a decent drop and the right sized tires. OEM rolling diameter for an 18" wheel is either a 215/45 or 235/40. If you have a coupe, the wider tire will fit nicely with a fender roll and not poke. If you have a sedan, fender roll, slight pull and some negative camber for either size tire. More pull and camber for the wider tire though.