I have tube tires. Do a lot of small drops (3-4 ft) to level concrete. Thrash down some pretty nasty rock fields. Will be going to Moab in a week or so, then Downhilling at Northstar. What is a good tire pressure to use without flats? Would it be different in Moab than at Northstar? I've heard maybe 25-35 psi. Would pressure differ in front or rear?