Traction Control Needed...

First off, ditch the air shocks before you crack your shock mount stud sheetmetal!
Get the springs re-arched or buy some new ones if they sag.
I can't understand putting a 215 on the rear if you are looking for traction, even for normal driving.
If you are buying new rear wheels anyway, you might look at a 15x7 and have more tire choices, especially if you might ever want a drag radial at the track.
I can't tell you if a 245 or 255 is the biggest you can run, but the limiting factor on that car will be the fender wells before you ever hit springs.


I run a 15x8 with 275/60/15 and 4.25" backspace leaving 3/8" clearance to the springs and no rub, BUT with folks in the back or bad bumps I get a little on the fender lips. Point being, you need to get your tires as far inboard with backspace and maybe offset hangers, to run any serious tire size.