What specific size rim diameter are you running? The bigger the rim diameter, the less you can safely air down since you have less sidewall with the bigger diameter rims. Less sidewall means you need more pressure to keep the tire from de-beading as it flexes.
On 35" tires with a 16" rim, you'll have no problem going down to 12 psi while driving slow, like 15 mph or less. This is a great sand & flotation pressure. For the "oh ********" moments, I've gone down to 10 psi to get through some super soft sand terrain in my big heavy Suburban with 35" tires on 16" rims. For two tracks, gravel and washboard roads, I would run anywhere from 16 psi to 18 psi when below 25 mph. As the speeds go up, you need to increase air pressure for handling stability and heat resistance.
On 35" tires with 17" rims, maybe a low of 13-14 lbs...with 18" rims maybe a low of 14-15 lb for soft sand, snow, rock crawling, etc.
The best thing you can do is find an open dirt or gravel lot near your house, lower the pressures and see how the truck reacts. When staying under 15 mph, you can go very low and the bead will retain unless you're playing baja racer or hit a very large rock against the sidewall when turning.
In the comfort of your driveway you should remove one of your tire/wheels and deflate it and break the bead so you can learn to re-seat the bead with your air compressor, etc. Every tire and rim has its own idiosyncrasies and you won't know what that is until you actually try and seat the bead. It doesn't matter how many books or videos you watch, hands on technique is key. Think of brain surgery, you can read books and watch all the videos of a procedure, but until you crack open a lot of heads to physically do the job you won't get good at it. Tire repairs and re-seating beads is something that has to be practiced on the vehicle you drive. A one ton truck tire and wheel is going to have different tendencies than a 15" rim with P rated tires on a RAV-4.
When re-seating the bead, the most important thing to remember is to remove the valve core while seating the bead....it is so restrictive that is slows the air volume down too much and makes re-seating the bead very difficult.
If you're at 30 psi, you might as well leave the tires at 55 psi....not going to help. You have to get under 20 psi to start seeing a softness in ride for washboards and even lower for flotation on sand, snow, etc. As I stated above, the faster you drive and the heavier your truck, the more psi you need to hold up the weight. One my F350 4WD with a diesel, when running empty on the street I keep around 50 psi in the front and 45 psi in the rear. This makes the truck ride very smooth at highway speeds. As my weight increases due to loads or trailer weight I increase the pressures for stability and heat resistance.
Experiment, experiment, experiment...practice, practice, practice......you don't want to find out you can't seat a bead when on a muddy hillside road in the dark on a Sunday night.
