I want 18's,tirerack shows that 18 by 9 fits in the back and 18 by 7.5 for the front.Will this setup rub if I also lower it or will it rub when I turn the wheel to make sharp turns.

 

Two ways to find out, measure the clearance when the steering is turned full right of left and then measure the exact with and high of both tire and wheel. Or call of email Tire Rack and they can usually tell you if the combo you want will work.