Greetings all powerful and imperious Admin... You spotted the discussions we were having over in the Auto Tranny thread eh...

First I freely admit that I used to drop my pressures way down when off road and it wasn't until a few years back that I changed on the advice of a Comp driver when I asked him what to run in my newly purchsed Pro Comp Xterrains... his answer blew me away as they were MUCH higher than I thought.

Currently I run Coopers and I use the pressures recommended by the Manuf which incidentally are close to what I used in the Pro Comps

Cooper Tyres pressure recommendations (and indeed I have found them to be pretty good for my Cooper Disocverer's are MINIMUM (go higher for loaded truck)
Gravel - 32 PSI
Rough Gravel - 26 PSI
Rocks - 22 PSI
Mud - 22 PSI
Sand - 18 PSI

My truck is very heavy with the gear I carry and I actually run higher by about 2 to 4 PSI except on the Beach Sand around SWWA which is like Custard so I drop to 16 to 18. Get onto the hard packed southern beaches of the Southern Ocean and you can stay higher

Different people will have different views which is totally cool... I was advised that higher pressures have the advantages of
1 protecting the side walls... in LT tyres the tyre stands upright and puts the tread between the case and sharp objects
2 less chance of spinning the tyre on the rim
3 less chance of crap in the beads
4 less chance of popping a bead
5 less chance of internal tyre failure... the ply's are not "working" against each other as the tyre distorts laterally

BUT... the bottom line is 'The right presure is the one that works for you'. I just used the Manufacturer's recommendations as a starting point and found them to be excellent 'cept for the local sand conditions