There's a few variables that might influence what will fit. Many times the rear axle wasn't centered in car from the factory, so, one side might have more clearance than the other. In a stock wheel well, I found with the stock wheel offset, I could put a 9" wide tire and a 28" diameter one without rubbing anything. It's pretty close though, so, take some measurements to verify. Custom wheels with odd offsets might allow something wider, but, you may run into problems in the front if you want all 4 wheels the same.
