installed a set of 31" nokian rotiiva a/t tires on my '94 reg cab 4x4's stock 6" rims. They are quite crowned at the stock tire specs of 26psi front and 29 rear. I have been incrementally lowering the pressure to try and get the proper tread contact with the ground. observing road salt/grime on the tread (chalk test), I can tell there is not full contact at 22psi front and 22 rear. If I had to guess, I think the fronts will be perfect at about 20psi and the rears slightly less, but didn't think this low was a good idea for on road driving.