I read the Nitto bulletin referenced earlier and I don't find anything in it that is misleading. I do, however, find that unless you start with the context offerd, the message is misleading.
For example, the concern raised here was that under-inflated tires generate excessive heat, and if this were not an issue, why would Nitto say it was? What Nitto says is that the IR photos they use show two tires 'at equivalent load' with pressures of 30psi and 50psi. The tire with the lower pressure ran hotter. The question is "why?"
The answer is in the next paragraph, bottom of page one of the bulletin. Nitto states therein that the 30psi tire was "under-inflated" while the 50spi tire was not. If not, then the 50spi tire must have been carrying pressure sufficient for whatever the "equivalent load" was, i.e., 2,601 pounds, since that is the example they are running in the bulletin.
Obviously, if you have a load on board that results in a per tire load of 2,601 pounds (10,404 pounds if evenly distributed over 4 tires), you would need to run 50psi and certainly would not want to run 30psi. Thus, the example is skewed in my opinion by the starting premise, that you are running a load requiring 50psi. Or is not skewed, the premise of the example is not as clearly stated as it could have been.
Of course, we generally don't run max loads with expedition type trucks. Nor would it be feasible (or all that illuminating from the perspective of Nitto) to draft a bulletin that discusses intermediate positions, such as running D or E range tires at half or less of their rated load capacity. Such discussion would lead to more confusion than it would resolve because everybody would then offer their own personal "what if" and the answers would vary for each circumstance.
Here Nitto is simply making a point, that if you have a load that requires, say, 50psi for the tire you have, running at 30 will cause elevated temperatures and might compromise the tire. No doubt.
What we are looking for is the correct pressure for our tires, not the maximum, and we can do that by reference to the Tire and Rim Association (TRA) load capacity chart published for reference purposes by that association. I found a copy of that chart on the Toyo website, and there are doubtless several other sources for that chart. We can use the same example that Nitto used because as it happens, it is the same tire size that we have been discussing here in regard to Nissan Frontier/Navarra: P265/75/16 versus LT265/75/16. Nitto states that the P265 tire needs 35psi to carry 2,601 pounds. Fine. But does our truck actually carry anything even close to 2,601 pounds per tire? No. So, what would be the correct pressure to run in such a tire given the load that we do carry?
Determine the actual weight that you carry at GVWR (always assuming you will never overload your truck), determine the weight bias for your vehicle (50/50, 60/40, or whatever), and determine the gross weight each corner of the vehicle will need to carry. Pick a tire size, then refer to the chart.
For the Frontier at 5,600 pounds gross with a 60/40 front weight bias, each front tire will carry no more than 1,680 pounds, and each rear tire will carry no more than 1,120 pounds per tire. None of these weights comes near 2,601, so we can assume going in that none of the tires really "needs" to be inflated to 35psi for the P-metric or 50psi for the LT style tire. The needed pressure is going to be less roughly proportionate to the lesser weights actually to be carried.
The TRA chart for P-metric 265/75/16 tires shows a minimum value of 2,249 pounds at 26psi. Even if we downgrade the P-metric load capacity by the 1.1 factor discussed in the Nitto technical bulletin, at 26psi, the P265 will carry 2,049 pounds. This value is still well over the per tire load carried by the Frontier at GVWR.
The TRA chart for LT tires shows a minimum value of 1,910 pounds at 35psi for the LT265. Obviously this "heavy duty" tire is able to carry less weight pound for pound than the P-metric when used at the low end of the application scale. But still, at 1,901 pounds, the load capacity of the LT at 35psi is still above the maximum load any one of the tires on the Frontier will need to carry, and only 139 pounds less than the P-metric equivalent tire. Thus it is safe to use the LT265 in any station on the Frontier running no more than 35psi, which is the manufacturer's placard pressure for that vehicle.
If a difference of some 300 pounds of load capacity (1,910 v. 1,680) is not sufficient safety margin for you, or if you feel that you might take a fully loaded vehicle into dangerous terrain which will place more than a fair share of load on any one tire, you might want to adjust your pressures accordingly, but to simply say that just because you are using an LT instead of a P-metric, you HAVE to increase your tires pressures by 10 or 15 psi disregards the facts published by TRA and the various manufacturers and oversimplifies the problem. In this case, the needed pressure is about 9 pounds over the P-metric pressure for the roughly equivalent LT tire, but only when the pressure of the P-metric is adjusted downward to start with to compensate for actual load. In fact, both tires can be run at the placard pressure of 35psi without causing havoc.
So, to answer the original question about the Nitto bulletin, I find nothing in it that is misleading, deliberately or otherwise, but I do find that the information can be confusing or misleading if the bulletin is not read carefully. I am sure that was not the intention of Nitto.
