Some folks think airing down (lowering tire pressure) is not really necessary and while that is true for some vehicles, there are reasons why you may want to air down regardless of your thinking on this, even if you have nitrogen in your tires.
A vehicle aired down properly to a nice flat optimum tread footprint rolls more easily mostly over the sand rather than mostly pushing down into and thru the sand with hard tires. Thus less torque is required to move the vehicle and less strain on the engine and drive train.
Additionally hard tires tend to give short way less than a full revolution spins as they push thru the sand. This kicks back a little sand forming a washboard / speedbump affect in the sand. The ride is thus more uncomfortable for you from the spins and very uncomfortable for those following.
Now some don’t want to air down because they worry about tire damage / wear on pavement and many carry portable pumps to air up immediately after coming off the sand or at least as soon as they can get to an air station. This really is not necessary if you are at the optimum flat footprint. I air down upon arrival and sometimes stay that way for weeks, only airing up if say I’m going to go from Salvo to Nags Head area. Over the years and many sets of tires I’ve seen no appreciable difference in tire wear than what I would expect at full street pressure.
Now that said there are things to consider when aired down. More sidewall heat is generated as the sidewalls flex more, but if speed is kept reasonable (even 55 mph or less) for the short distances you would travel around the beach area on pavement, it would not be a problem. Also handling, especially in sharp cornering, is affected as the tire tends to “roll” more to the side of the rim in a turn. But again, reasonable speed and avoiding sharp cornering should give no problems. Gas mileage is slightly affected as it takes a little more effort to move the vehicle.
Now you can air down “too much”. When you go below the optimum flat footprint the center of the tread tends to concave in toward the rim and even in the sand you tend to ride more on the tread edges and the hump of sand in the middle adds to the torque required to move the vehicle. While not as bad as hard tires in the sand, it will tend to result in more “digging” from just the edges and pushing thru the sand. And it will cause excessive tread wear on the tread edges on pavement, plus way more heat in the sidewalls.
In addition sharp turns at very low pressure, as in trying to move over out of ruts, can result in breaking a tire to rim seal. Plus if torque is applied when you start to bog down the low pressure can result in the rim spinning inside the tire if the edges “grab” the sand again breaking a seal. I’ve seen this happen on a couple of occasions, one having two seals broken, thus no help from the spare.
Here is a site that discusses 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 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.
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When driving in the sand, slow steady progress is best. If you start to bog down, stop. Back up a few vehicle lengths in your tracks and then go forward again with slow and steady. Try to avoid spinning / gunning it as this will generally dig you in.