yes I know but anything is better the my stock 17 inch GM wheels with 265-70-17 tires. At least the larger rim and a little more heigh/width of the 18 tire will fill up some more wheel well until I stop being a wussy and pull the trigger on some 275-70-18s but they only come in ten ply and range E.
if there was a larger tire that wasn't 15 pounds more then my oem set up that would kill my MPG I would do that.
but again anything is better then my stock wheels and tires IMO