The link in the air down post for optimum footprint no longer works, so here is the info.
The optimum footprint for sand.
It is not a one size fits all so you will have to experiment a little to find what fits your setup. Your vehicle should roll (float) rather easily over the sand and not require a lot of extra power (torque). And remember street pressure is not necessarily exactly what is on the door placard. The placard is nominal for a nominal load (usually indicated on the placard). Both street and sand pressures are load dependent (including passengers, gas, etc) and may vary front to back, depending on how you are loaded.
Here is a place to start on airing down. Works for radials; don’t know about others.
Load your vehicle, including passengers, like you will have it in the sand. On level pavement with the tires at street recommended pressure, measure the height from the pavement to bottom of the rim. Remember recommended street pressure on the door placard is nominal so more or less load means more or less pressure. And the height can vary front to back, depending on load, so measure both.
Then drop the pressure until the height is ¾ of the street pressure measurement. This will give a nice flat footprint that will roll (float) easier over the sand rather than pushing down into the sand as hard tires tend to do. Lowering the pressure more generally does not gain you much and it can concave the center of the tread in toward the rim and thus you are riding more on the edges and that can also tend to dig you in.
With the flat footprint you can also drive on pavement without fear of excessive tire wear because you are not riding just on the edges. Now that said you want to keep speed down on pavement because the extra flex in the sidewall can generate excessive heat and that is where damage can occur.
I have used this for decades, staying aired down for weeks at a time, and have seen no noticeable degradation in tire wear. Just keep my speed at about 45 mph max, particularly in hot weather and don’t do long trips. But never hesitate to do a 60 mile round trip up and down Bodie, Hatteras and Ocracoke Islands.
For my 4Runner this works to about 20 +/- 2 psi, give or take on load.