Dave is right about the 31's not fitting without a lift. I have a 1.5 inch body lift, Eibach springs in front, with the spacer on top of the strut. It's probably at least 3" of suspension lift and 1.5" of body lift, and when I run 31" mud tires, they STILL rub the plastic bumper in front on the passenger side when the wheel is fully turned to the left and I'm backing out of the driveway. This is after I cut off some of the metal fender to the rear of the wheel well, and I also cut away the metal seam in the underside of the wheel well. Before I did that it also rubbed at the back of the wheel well!

I think you will NEVER fit 31" tires without a lift.

Just for your reference this is how my Sporty looks with the 31" mudders: