Tire and Rim Dilemma

You can't fit a 255 on the back? I have 235/60R15s on the back and they look puny. I can EASILY fit a 255/60 on the back. I'm thinking of trying for a 275/60 IF the diameter isn't too much. I would REALLY like a 295/50, but that would definately require rolling the lip on my car.

I have 15x7 on the front with 215/60 and there are no clearance issues.