[JRTJH]

When you consider that the temperature sensor in any TPMS "stem system" is going to measure the temperature "at the end of a stalk, 1.5-2.5 inches out in the airstream" and that "stalk" may or may not transfer heat as efficiently as the wheel, rubber tire, air inside that rubber tire might transfer heat, then add in the "cooling effect" of that "temperature sensor" slinging around in the atomosphere, sometimes aided by cooling humidity, sometimes hampered by "scorching sunlight at high noon" and you'll begin to get the idea that temperature "measured by a TPMS valve stem cap" is, at the very best, a close approximation of reality.... Then when you add in all the variables encountered, you can easily come to the conclusion that it may very well not even be a "close approximation"....

TPMS "external sensors" don't do a very good job of "sensing internal tire temperatures".... About the only "close to reality" is to compare both the sensors on the shady side of the trailer and compare both the sensors on the sunny side of the trailer. If each "pair is somewhat close" then that's about as "much temperature reality as you'll get" from a "stem cap TPMS" readout.

Think of it this way: Aim the red dot from an infra-red thermometer at a mirror, bounce the reflection off the mirror toward the tire and judge whether you're close or not to reading the area of the tire where you're concerned with temperature.... Your TPMS may (or may not) be as accurate as the reflected red dot reading.....