i have 4 17x9.5 wheels...but i want to get 2 18x10.5 wheels for the back.......i have found a pair with a 54 mm offset...will i need to do any modifying to the fender wells? or will they fit in there ....i am at stock height

 

You may have some issues with the inner sidewall of the tire rubbing on the inner fender liner. That width/offset combo puts the backspace at about 7.85", and that's within 1/10th inch of the typical 11" wide/50mm offset dimension. Look at the writeup in the FAQ (stickied at the top of the Wheels and Tires forum topic listing) on the 17x11 wheels, and where you might have problems. Obviously you have a little more clearance (1/10th inch), but with wide tires, you may still have rubbing. You would also need to make sure the inner edge of the rim does not catch on the jounce bumper bracket when you jack the car and the axle goes to full drop. Check the FAQ for info and photo links.