Another important factor in wheel and tire selection is the location of the rear leaf springs in relation to the surface of the axle flange. Once the depth is known, it can be compared to your backspacing to determine if there's enough clearance between the wheel and the spring. | 
This perspective of the installed wheel shows how close the wheel and tire will come to the spring. Our 17x9.5-inch wheel with its 5-inch backspacing is a cozy but workable fit. By the time we allow for tire sidewall bulge, there will be less than 1 inch clearance on the inside edge. | 
Even stepping up 1 inch to a 15-inch wheel will make a big difference in the way your car looks and handles. These American Racing Torq-Thrust D wheels along with P225/55R15 tires make a nice first upgrade, but even this modest size improvement should be checked for clearance in all dimensions. |
When installing a larger wheel and tire assembly, be sure to check for interference at the control arms, tie-rod ends, and shocks. This 16-inch Vintage 45 wheel will have no problem working in the wheelhouse of a '69 Mustang. | 
We recently measured for custom wheels on a project car at Classic Creations of Central Florida for the installation of a 17-inch wheel package. After checking our caliper clearance, backspacing, and wheel-house dimensions, we settled on our wheel and tire choice. The wheels are Wheel Vintiques Billet Bullet sized 17x9.5 in back and 17x8 in front. Our tire choice is a Nitto NT555 P275/40ZR17 sized for the rear axle and P245/45ZR17 for the front axle. With the tire mounted, the assembly tucks up into this '65 Mustang rear fenderwell quite nicely, though this axle has been narrowed and the rear leaf springs moved inboard for larger tires. In this tight rear tire installation, be sure to check the positioning of the parking-brake cables because they can rub completely through the tire inner sidewall in a mile or two, and you won't hear it happening-although you might smell burning rubber. | 
This installation of a 17-inch Cragar SS wheel on a '65 Mustang is a much tighter situation and near the limit on the early car. Be sure to check this arrangement for clearance problems by cycling the steering wheel lock to lock. On cars with power steering, it is especially important to check for interference at the power-steering hoses. |