I purchased a set of 17x8 94 mustang cobra rims for my 73 mustang and discovered yesterday that they will not fit on the front of my car without wheel spacers. The backspacing on most late model rims is 5.45 or greater. Because the 71-73 mustangs originally had wheels with 4.25 inches of backspacing, clearance problems occur when trying to install late model rims.
The 94 cobra rims came in contact with the upper control arm and the tires I installed also came to within an inch of touching the frame on my mustang. Of course that was with the steering wheel turned all the way to one side. With the steering wheel centered the rims still touched the upper control arms but there was plenty of room around the tires.
I decided to go with 245/45/17 tires and had them installed on the cobra rims. I used a tire size conversion calculator to estimate the tire size that came closest to the old tire diameter on my 14-inch rims so my speedo would still be somewhat accurate.
Anyway to correct my problem with the cobra rims I am going to install 1-inch spacers on all four corners. That will get the backspacing back where it needs to be. The 1-inch spacers are made of aluminum and actually bolt onto your spindles and axels. The spacers have a set of studs installed in them where your wheels mount. They run around 100 bucks a pair but I have seen some on ebay that were 150 for a set of four.