I might have 15x8s.. I'm not sure. I have AR Baja chrome wheels with 31x10.50 tires now and the tread sits flat across, but they are almost shot. I bought the jeep with the wheels on them and there are no markings visible.
EDIT they are Mickey Thompson classic 2s. I went to there website and they only make 15x8 15". So a 12.5" tire would be ok for them?