I'm running ~24psig rear, 26psig front on mine with P285/70R15's & the same fronts you're running. I did the chalk check for the rears, using kid's driveway chalk to put a heavy mark across the tread, drive 50' on asphalt and stop to see how much is worn away. Started at 30psig, dropping a pound at a time before it wiped the whole width pretty even at 24psig. Fronts are pretty narrow, so I just bumped them to 26. Getting an even wipe shows you an ideal contact patch - best for grip, for longest wear, and more comfort, too. It's an old Jeep trick, running big meat with light weight, and trying not to wear the big, expensive tires out in the middle by running "recommended" pressures for trucks.