Unless the front brakes are bigger, there's no reason to go 18".
I'm sick of this common trend of cars getting bigger and bigger wheels for no purpose other than just to "look cool".
Same with all these people stretching 205's on 8" wheels... makes no sense. Adding more weight, and still having the same contact patch as if you just kept 205's on 7" wheels... If you're gonna go wider, at least get wider tires to make it worthwhile of adding the extra weight.