Maximum Tire Width: It’s a good idea to make sure the tire you are buying will fit on your rim, not only in the way of diameter, but also in width. A standard 1987-1990 Mustang GT Turbine wheel is 7" in diameter. The stock 225mm tire is 8.86" wide at it’s widest point. Going too wide puts dangerous levels of side loading on the rim which can result in dismounting or catastrophic failure. Side load on the wheel is not only dependant on width though. It’s also dependant on aspect ratio. The taller the sidewall, the less pressure there is on the rim because it can gradually flex the tire down to rim size. To illustrate this, the P275/60 has been mounted on the stock turbine wheel. It’s too big for maximum tire performance, and it borders on being dangerous, but some people have managed to get it on the rim (not the car without removal of quadrashocks or at least reversing them). Just try and get a P275/45 tire on the stock turbine rim. If you manage to accomplish the feat, it’s going to be an extremely dangerous combination. Another problem related to side loading a rim with too wide a tire is the contact patch of the tire is reduced. As the rim presses the tire in at the bead, the edges of the tread are actually pulled away from the roadway because of the pressure. This results in a less efficient contact patch. Expect this to start taking place with any tire over 245mm on a stock turbine.