Kronix,
Check your tire sizes. Proper sizing is
225/40x18 - 265/35x18
225/35x19 - 265/30x18
Stick with those and you'll get the optimum performance. Your car isn't designed for super fat rubber. Besides, bigger = heavier and heavier = slower, both in a straight line and around a corner.
If you're going to customize then do it right. Don't turn the Boxster into a "Ricer"
