Tuesday, December 5, 2023


More on internal vs. external TPMS temperature reporting

RV Tire Safety
with RV tire expert Roger Marble

Continuing my series on Tire Pressure Monitoring Systems. Last time I covered internal versus external TPMS temperature reports when it was moderate to just cool outside. This report is different. On my way south to Georgia from Ohio it got downright cold.

I stopped for the night in Kentucky and in the morning I obtained these readings.

Internal System:
RF 30   LF 32   RRO 32   RRI 32   LRI 30   LRO 32

External System:
RF 32   LF 32   RRO 32   RRI 32   LRI 32   LRO 32

As expected, the temperature numbers were essentially the same. To me this confirms that the sensors can report ambient temperature if given sufficient time to cool to ambient temp.

After about an hour running down I-75, I observed these temperatures when the outside temperature was in the 40’s:

Internal System:
RF 86   LF 83   RRO 85   RRI 86   LRI 80   LRO 80

External System:
RF 48   LF 48   RRO 46   RRI 44   LRI 57   LRO 55

These numbers clearly show that the external sensors are reporting significantly cooler temperatures than the internal sensors. With cooler ambient the difference from internal to external is greater than when the temperatures were warmer.

I previously suggested that people running external sensor TPMS might consider adjusting their high temperature warning level down by 10° F to 15° F.  While the above might suggest lowering from 158° F to maybe 135° F, I am not sure if this would be too cool for people that are traveling when the ambient is above 85° F.

For now you might just want to be aware of this difference. I am hoping that later this summer when I am traveling I will be able to get measurements when the ambient is above 85° F.

Read more from Roger Marble on his blog at RVtiresafety.net.


Roger Marble
Roger Marblehttp://www.RVTireSafety.net
Retired Tire Design and Forensic Engineer w/50+ years of experience. Currently has Class-C RV. Previous Truck Camper, Winny Brave, Class-C & 23'TT. Also towed race car w/ 23' open trailer and in 26' Closed trailer. While racing he set lap records at 6 different tracks racing from Lime Rock CT to Riverside CA and Daytona to Mosport Canada. Gives RV and Genealogy Seminars for FMCA across the USA. Taught vehicle handling to local Police Depts



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Bill McFarlin (@guest_22401)
5 years ago

Using the monitors to compare reading is what should be done. After 20 minutes or so on the highway check the temperatures and pressures and after that watch for any sudden changes, and if there are check the tires as soon as possible. I have one sensor that occasionally gives me a “high pressure” alarm and yet the temperature is normal, there is absolutely no possibility of this happening so I monitor it and continue on my way.

Jeannie (@guest_22362)
5 years ago

I assume (accept) that TPMS sensor readings, especially for temperature since they are external sensors, will not be accurate and, frankly, I’m not worried about it. I depend, instead, on mine to tell me when one tire’s readings are significantly different from the other tires. One tire that heats up faster than the others could be a sign of a dragging brake (in the case of my spare, it’s the nearby exhaust pipe). Of course, the sun hitting the tires on one side when parked will also result in much higher temperatures; they usually even out, more or less, after driving a little ways. One tire having significantly lower pressure than the others when temperature readings are pretty much the same are an indication that something is probably wrong and should be checked out immediately. A rapid change in the reading of one tire is another indication something may be wrong and should be checked out.

I glance at the readings before starting out and occasionally while driving but I don’t obsess over them. There are reasons for the alarms in the TPMS. They allow me to concentrate on the road instead of the TPMS monitor.

Paul Sebastian (@guest_22361)
5 years ago

Can you recommend an internal TPMS system?

Roger Marble (@guest_22399)
5 years ago
Reply to  Paul Sebastian

Paul, I’m not quite ready to recommend an internal TPM system yet. I do have some observations on the new TST internal system I am currently evaluating. Maybe the best I can do so far is to give some of my initial Pros & Cons. Remember I may change my opinion on some of these after a few more trips.

TST internal System
More accurate tire temperature numbers.
Color display nicer to look at

Initial installation cost ($109 in my case) in addition to purchase price
Display battery life is shorter (maybe because the backlight for the display is always on)

TT500 External system
No cost to install
Display battery life is a week or more of drive time

Less accurate temperature reading.

I still have some tests to run:
Air loss report time
Hot weather temperature comparison

Test I cannot run
Battery life of the internal system

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