that's going to through off the speedometer as well as the odometer.. 225/40/18 is 25.09" high while the stock 255/35/19 is 26.03" high. Not to mention it will be worse in the snow due to the gear ratio effect that will make all the gears ratios slightly lower. 18's in the rear should be 255/40's, as they will have the same overall height but with a smaller rim.