picked up some iroc rims off craigslist with decent tires.. at least the fronts are.. they're 16 x 8 and labled front and rear.. only difference is the rears have a 20mm less backspacing so they sit in closer to the center of the car... somehow these wheels / tires work on an iroc.. but on my 86 firebird (all stock). the tires will bottom out in the rear when turning or over a bump. not sure what is hitting.. maybe the rubber bumper right above the axle.. seems pretty close the inside edge of tire... so does anyone know what's going on here? why do these wheels not seem to work on my car? is there a way to make them work?

 

What size tires?

 

Sorry... it's just the stock tire size 245 50 16

 

There's no reason for it not to work because the car is exactly the same in the rear between the two cars. The only possible thing that I can think of is that maybe your rubber bump stops are gone or damaged so the rear is rising too close to the body, which is causing a tire rub. Aside from that, the only other real possibility is that something is wrong in the rear of the car... damage to the inner wheel well, panhard rod is broken, etc.