Off-road is one thing but I'm wondering about on road. I've got 31" Bridgestone Dueller MT's on my Zuk which has got 2" longer shackles and a BDS 4" spring lift. This was all recently installed so I have no idea what tire psi to run!
I run about 20 ish round town, 30 on longer trips, and about 5 on trails. I have super swamper tsl sx tires 29x10.5 that do not flex..
I did get the back end to flex a little when I had 2 tires off the ground.
I run Dueller A/T's, and run 35 psi on the highway. And "on the highway" includes one snake of a road (Golden Gate Canyon west of Denver). I corner hard and fast. The AT's prefer the higher pressure for optimum cornering. I'm getting good wear, and great handling (and 30 mpg).
i run about 30 on the street with 33x12.5 just to make it easy to steer. and it seems to run faster. used to run 20 but it hurt the miliage and steering. off road about 4 psi on 10 in rims and i have never lost a bead.
in my 16x35" Boggers I run about 2-5psi The last time I ran off-road I went down to 8psi and seemed to work fine. The bogger flexes well over rocks when aired down to about 2psi, the light weight of the zuk doesn't help out much. I hope after I install the toyota axles and v6 engine, it will be a little better.