what is largest wheel and tire for 73 mach 1

not 1999 svt cobra, tried them on my 73 stang, they hit the upper control arms.

I have a 1973 mustang with 21 inch rims on the back and 18 inch rims in the front. In order to get that big of a wheel on the back you need to put air shocks on the car to lift it up higher. You can also try a shakle lift kit in the back but make sure the metal bars are thick enough because mine werent and they bent from the weight. The best way is to get the air shocks but they are expensive mine were $800. Hope this helps.