I Just bought a 2000 Mustang GT in october and I went to the tire racks website and put in the year make and model of my car and it said the original equipment is 225/55/16 and then I went to discount tire and put in the same information and there website said the original equipment is 245/45/17. So which one is right? My car is garaged right now but I need new summer tires soon. I went and looked at my car and the tires that came with it are 225/55/16. So were there supposed to be 17's on it or what? Also is there a machine at tire places that can tell me exactly what the biggest tire is that I can put on? I want the widest tire I can get this summer but I dont want them to rub obviously and I dont want to do any modifications to the wheel well.