Internal vs External TPMS comparison Hot ambient

Since March I have been conducting a comparison of a couple different TPM systems. One from TST has internal sensors, as seen here.

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 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 here.

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 location. 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 brand or the different sensor location.

To accomplish this I mixed the external sensor brands and used three external sensors from TST vs three from TireTraker. Here are the numbers.

Ambient was in the upper 80s to lower 90s for this part of the test.

Internal vs External TPMS test results

All temperatures are in °F and pressure in Psi
Internal System.            
Temp.  RF 102   LF  102    RRO  104   RRI  109   LRI   113   LRO  106
Press          69           70                 82              84              84              86

TST External System
TEMP    RF  86                                      RRI   84                         LRO   86
Press           70                                              84                                  86



Second run
Internal System.            
Temp.  RF 108   LF  111    RRO  115   RRI  124  LRI   117   LRO  109
Press         70           71                 84              87              84              87

TST External System
TEMP    RF  79                                      RRI   90                         LRO   82
Press           71                                               86                                    87

Tire Traker External System
TEMP                    LF  78     RRO   100               LRI   91
Press                          70                  82                         83

Now 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 20F to 30F cooler than TST Internal temperatures.

TST system internal sensor pressure vs external sensor pressure readings Tire Traker are essentially the same
TST internal temperatures readings run 15 to 33 (average 25F) hotter than Tire Traker 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 20F to 30F cooler than internal sensors for both brands.


BOTTOM LINE
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 so will report 20F to 30F 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.