TPMS / TST507 Questions

GMandJM wrote:
Tire pressure and temp increase from the heat of driving (rolling resistance), heat of the day and such. That's why the manufacturer says to set your alarm settings 20 percent above and below your cold pressure settings. I do 25 percent.

There is a slight diffidence between cold pressure readings on the monitors vs the tire gauge, but not enough to be of any concern since it is consistent. I always use the same gauge for continuity.

Are you sure you want to only get warned after loosing 25% of your air pressure? I don't know what brand TPM you have or if it warns when you are 25% below the cold "set" pressure or after you loose 25% from the high hot tire pressure.

If the pressure you need to carry the measured load on the heavy end of the axle is 90 you might consider your normal morning cold pressure to be 100 as it's nice to have a margin so you don't have to go chasing for air whenever the temperature drops 10 degrees.
A good TPM will offer a "rapid air loss" warning the warns after loosing about 3 psi in a couple of minutes. This means that if your hot pressure is 111 and you get a leak you would get an initial warning at 108.
This would allow you and the co-pilot to start looking for a safe place to pull off while you monitor the air pressure. You might even have a number of minutes before you drop down to 90. You certainly want to pull over before the pressure drops to 78 psi as that is the 20% figure tire companies use to identify when damage can start to occur to the tire from running "flat".

If you only get warned after dropping 25% under the set pressure you have a good chance of having already done permanent damage to the tire.

RambleOnNW wrote:
We have the TST system, flow-throughs on the rear and non-flow-throughs on the front. During the summer I can count on the pressure increasing on the rears by about 12psi from the cool of the morning to the heat of the highway. The sensors read 2-3psi low when cool but they match the reading of my digital tire gauge when hot.

Ambient temperature increase of 10 degrees F will cause a pressure increase of 1 psi. The other pressure increase is due to tire heating from flexing while rolling, and also heating from rolling on hot pavement.

Sorry the 1 psi for 10F may be close for passenger tires but the better figure to use is 2% for 10F change.

We have the TST system, flow-throughs on the rear and non-flow-throughs on the front. During the summer I can count on the pressure increasing on the rears by about 12psi from the cool of the morning to the heat of the highway. The sensors read 2-3psi low when cool but they match the reading of my digital tire gauge when hot.

Ambient temperature increase of 10 degrees F will cause a pressure increase of 1 psi. The other pressure increase is due to tire heating from flexing while rolling, and also heating from rolling on hot pavement.

I agree with the previous two postings.

ditto what he said above....Dennis

Tire pressure and temp increase from the heat of driving (rolling resistance), heat of the day and such. That's why the manufacturer says to set your alarm setttings 20 percent above and below your cold pressure settings. I do 25 percent.

There is a slight diffference between cold pressure readings on the monitors vs the tire gauge, but not enough to be of any concern since it is consistent. I always use the same gauge for continuity.

As temp goes up, pressure goes up, a little.

My TST reads about 2 or 3 pounds lower than my gauge. Not enough to concern me.