A 245/45/17 is pretty much the limit for the front on a Fox. And, it IS tight! That's assuming that you have a
stock height car. Otherwise, you may need to go down to a 225 up front.
BTW: As I've said a million times
, there is no such thing as a standard for tires sizes! Check tirerack! My 245/45/17's (RE730's) are among the widest 245's there are. Both in sidewall and tread-width. Cheap tires are often thinner. So, two different 245/45/17 tires can have different amounts of clearance between the fenders.
And, your fender height makes a difference also! Chances are your lower spring isolators are no more. That can result in a drop of ~0.05" -> 0.1". Not much. But, if you then have 0.05" interference, a 0.1" drop is a big deal.
Also, be careful about general advice from people. The
year makes a
difference! It makes a difference in fenders, k-frame mounting holes, and strut towers. For 4-eyes, the k-frame is also different. And, as I said, Stang drop over the years because the isolators wear out, and many people run cheap tires that have widths that are really a few down from the "tire spec". Again, check out the tire specs on tirerack.
So, that's it in a nutshell.
Most 245's
barely fit on stock height Stangs. Otherwise, 225's are the safe way to go. As said, for handling, you want 245's up front.
FWIW: My car:
http://www.veryuseful.com/mustang/tech/misc/Mustang1986_with_Mach1_springs/
As you can see, the tires barely fit. But, since my car is an '86 with
suspension mods, it doesn't mean those same tires will fit on your car.