It depends on WHICH stock rim it is. On the 05's thru 09's, the stock rims were anywhere between 8.5" and 9.5" IIRC. It should be stamped on the inside (side facing towards under the car) of the wheel.

 

Looks like they are just 8.5" wide. I guess I should stick with the 245 wide..

Im thinking about going with the Eagle GT. I would love to do a summer tire, but unfortunately I do have to get through some winters here and I dont have the extra cash for two sets right now..

 

Go on tirerack's website and look at the specs for the tires you like. The specs will tell you what the widest tire that you can safely put on an 8.5" wheel. IIRC, it's 255's.

Be aware that all-season tires are pretty crappy in snow and the Stang simply compounds that by being so light over the rear tires and having a lot of torque. If you can swing it, get a dedicated winter tire and put about 150 lbs in the trunk for winter. If nothing else, add weight to the trunk and hold on. I drove in the philly/south jersey/ York, PA areas for over 35 years (plus 4 years in Detroit and 1 year in Chicago) and all-seasons are nothing but a poor trade-off.

 

Unfortunately two sets of tires isnt really doable right now. I wish it was.. If all seasons arent worth it, should I just skip the all seasons, go with a set of summer tires, throw a bunch of weight in the trunk and drive cautiously in the winter? I feel as if this is the question of all questions when it comes time to tires...

 

If you can only do one set then go with all-seasons; better than summer tires in the snow but still woefull in a number of areas if you ask the tires to really perform. For most dry and wet "normal" driving, they're ok. The rating info on tirerack is helpfull but don't bet your life on it. Careful driving and some weight in the trunk and you should manage.