225/50/16 is as big as you wanna go on a 7 inch rim on an everyday driver. Anything over 2 inches is asking for sidewall flex and can make the car handle worse though you have more of a patch on the ground.
Kevin
I believe the pony's are 7" wide -- could be wrong though. Sicarius is right -- general rule of thumb is a tire no more than 2" wider in section than the wheel. The section width of the tire in millimeters is the first number in the size. So a 225 tire is (225/25.4 in/mm) is 8.85" wide in section. So, your wheel needs to be at least 6.85" wide. If you move up to a 245 section tire, you really need an 8" rim.
Don't misunderstand - you can MOUNT a wider tire on the narrower rim. The problem is that the sidewalls don't have the support they need to allow the tire to put all it's tread on the ground. So even though you've mounted a bigger tire, you don't have much more rubber on the ground than you do with the 225 tire on the 7" wheel. Furthermore, since the sidewall isn't supported like it should be, the wider tire on the narrower wheel will tend to roll onto it's shoulder more easily under heavier cornering.
Another issue - you may like the small tires front/big tires rear look. But the Stang is EXTREMELY front weight biased -- 57-58% on the front, the rest on the rear. The front tires provide 85% of the stopping power of the car. And of course, they have to turn the car as well. Even if you go larger on the rear, I wouldn't run anything smaller than a 225 section tire on the front. You simply compromise handling and stopping if you do. Not a good thing - especially on the street where you never know when someone else is gonna do something stupid, and you've got to ask your car to safely perform an emergency manuver.
I used BFG Comp T/A's in 245/50/16 all the way around on my '91 and it's a close fit but everything clears. My car has Steeda 660#/F and 245?#/ rear springs
Never seen an 8" Pony wheel and I looked real hard. All are 7" wide and would not work for my 245/45/16 tires. I did put on 245/50/16 and they worked for me real well. It may be pushing it but I found that the stiff sidewalled Yoko tires worked real well. Now that I have Cobra R wheels that are 8" wide the feel I get from my car is not that much different than the Ponys with the 245's!!
my ponies have 225/50/R16 Toyo Proxies and they look good. They seem to be good tires to me, although my back ones are nearly bald
I think I'm gonna throw my tires/wheels from my GT on my LX though because I can't afford to buy new tires right now. Otherwise, I'd replace the tires on the ponies w/ more toyo proxies 225/50/R16.
I know I've read that 245 in the front rubs at full lock.
Tire manufacturers usually put a minimum rim width for each tire size. As long as you abide by those rules you aren't running outside of the manufacturer's specifications and you should be fine.
Most of the 245/50/16 and 255/55/16 have a minimum tire rim width specification of 7". Is it optimal for traction? Not really. Will you damage the tire or kill yourself running them? At least the tire manufacturer doesn't think so.