Internal vs. external TPMS comparison – Hot ambient temperature


RV Tire Safety
with RV tire expert Roger Marble

Since March I have been conducting a comparison of a couple different Tire Pressure Monitoring Systems (TPMS). One from TST has internal sensors, as seen below right.

Please note this shot shows the TPM sensor and the steel band retainer. I was in the process of removing the extra band material as this is a 16″ wheel. A larger wheel would need a longer band.

The other system from TireTraker has external sensors that screw onto the end of your metal valve stems, or as I did on the end of my dual tire extension hoses seen below left.

I also had some TST external sensors that mount on valve stems and look very similar to the TireTraker brand sensors.

This is the final post on the direct comparison of different sensor locations. I previously posted results HERE, but there was a question raised as the internal system was one brand from TST and the external sensors were from TireTraker. We needed to learn if the minor differences were due to the different brands or the different sensor locations.

To accomplish this I mixed the external sensor brands and used three external sensors from TST versus three from TireTraker. Ambient was in the upper 80s to lower 90s for this part of the test. Here are the numbers.

Internal vs. external TPMS test results

All temperatures are in degrees Fahrenheit and pressure in psi.

TST External SystemRF  RRI LRO
Temp.86  84 86
Pressure70  84 86


TST External SystemRF  RRI LRO
Temp.79  90 82
Pressure71  86 87
TireTraker External System LFRRO LRI 
Temp. 78100 91 
Pressure 7082 83 

I realize that reading the above doesn’t make the differences and similarities obvious or even easy to see, so here is a summary of the findings:

TST system:  External vs. internal pressure readings are essentially the same.

TST system:  External temperature readings run 20 F to 30 F cooler than TST internal temperatures.

TST system internal sensor pressure vs. external sensor pressure readings from TireTraker are essentially the same.

TST internal temperatures readings run 15 F to 33 F (average 25 F) hotter than TireTraker external temps.

Reviewing the above results and the results posted in the July 20 report and the two March reports from tests with ambient in the 30s and 40s, it is my considered opinion that both TST and TireTraker systems provide similar numbers for inflation pressure and that external sensors report temperatures that are 20 F to 30 F cooler than internal sensors for both brands.

Given the above comparison on the data readings I would consider these two systems a toss-up for reporting the temperature or pressure, as long as you remember that external sensors are being cooled by external ambient temperature so will report 20 F to 30 F lower temperatures.

There are some differences between the two systems and some of these are subjective. I will cover these differences in a future post.

Read more from Roger Marble on his blog at



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