Depends on what ply tire you have.
I air down to about 18 psi in both parks. I run an E Rated (10 ply) Mud Terrain tire.
If you have the stock tires that came with your rig, either upgrade them to C or E rated tires if you can, or go really slow on the roads out there.
Like everyone before me has stated, have at least 1 spare, a GOOD compressor, a tire repair kit that you KNOW how to use, a good jack, lots of water in case you get stuck...
