I agree whole heartedely with bushpilot, the temperature function is just as important as the air pressure. You set the alarm for a drop in pressure, or an increase in temperature. Either is a sign of impending tire failure. And he is correct you will see the tire temp go up if you have a bearing or brake problem developing. I once had an emergency brake not completely release and was rubbing slightly. Ninety miles later I finally noticed when the red hot backing plate blew the seals out of the wheel cylinder, the brake fluid caught fire, and I saw flames flickering in my rearview mirror. "Luckily" it was night time or I wouldn't have seen that either. A tire monitor would have sounded as soon as it started to get hot. It used to be my habit at every stop to do a walk around, visually inspect each tire, thump it for pressure, and lay my hand on the wheel to check for anything too hot. With the tst system all I do is the walk around and visual.
It amazes me watching the readout how much the temperature changes in the tires. Pressure, outside temperature, speed, load, even which side is in sun/shade all make a noticeable difference. When I had 15" load range D tires on my trailer I was having tons of tire problems, even though when I scaled it I was within the rating of the tires. But I found that as my load got closer to that point, the tire temperature went up dramatically. And the temps went up far more than the pressure. Even a 1000# difference in the load on a triaxle trailer made a difference. Also the speed, the tires were running way hotter at 65-70 vs. 55-60. Eventually I upgraded axles and went to 17.5 tires and tire problems went away, but I learned a ton with the tst sensors on saving tires, and still run them. The 17.5's were the second best money I ever spent, in a season and a half I have literally not even had to add air to the trailer tires, the spare has never been on the ground, and I was going through 5-6 tires per season before that. I never left the shop without at least 2 spares.
While it is correct to say that the pressure needs to be the same in both dual tires, out in the real world it is not critical that they have to be precisely the same. The theory of course is that the tire with the higher pressure will have a slightly larger diameter meaning it is supporting a bit more than it's fair share of the load, and with the larger diameter the rollout is slightly bigger so the surface of that tire is travelling just a bit faster than the other tire causing faster tire wear. So, like I said out in the real world, you would have to have a pretty serious difference in the pressure for any of that theory to translate into enough reality that you'd notice. 5 or 10psi on a heavy truck tire is not going to make an appreciable difference in any of that, and you can certainly keep track of that with a set of monitors and gain all the other benefits at the same time.
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