[9TOFIVER]

well first off 18's aren't the best for performance in handling, its all in the width of the tire not the height. In other thought, i would first put on the 18's see if there is a gap in between the tire and wheel well that you wouldn't want there, then if there is ,lower it down to where you want, make sure you get Adjustable Springs, so you can lower it down to where you want it.