Ya know, you can probably get 275s back there now. I can put 245s in back right now, just have to move the axle over about 1/2 inch then I will barely have the clearance necessary to do that. You got a tonna room now.
All depends on your tire/rim package and your desired use of the car. Short stiff sidewalls on larger rims will flex much less than higher profiles on 15" rims like mine. Drag strip use you can get away with very tight clearances but a cornering car needs more. This one is going to get flogged on curvy back roads so I shot for 1" clearance on both sides as I don't want to hear any rubbing.
