Go to performance wheel outlet. I did this last summer, I have a 66 coupe with Bullitt 180 series wheels, they are 17in. with a 4.5 in. back space. I run 245/45 17's in the rear, and 235/45/17 in the front. I dont have any problems as of yet! However if you intend to really lower your rear, it may rub about an 1/8 in. on the wheel wells, if you have a load of people. Mine is stock height with 5 leafs and no problems yet.