I purchased two things for the trailer. One was a tire gauge and the other was the Tire Pressure Monitor System. First, I checked the pressure by use of the gauge (brand new). The tire pressure showed 110 PSI. After that, I installed a TPMS and noted that the Tire pressure was showing 115 psi (cold pressure). As the tire is used and the day increases in heat, the tire was showing 123 psi. what PSI should I follow? The first gauge that shows the psi to be 110 or the tpms which shows the pressure to be 115. Or should I decrease the amount of air, putting the tpms as priority, in other words putting the psi to 110 down from the reading of 115?

All depends on the QUALITY of each item there is a lot of junk out there.

Yep, just depends on which is the better quality. My pressure gauges and my TPMS agree to the pound.

My TPMS monitor is adjustable to set pressure close to a regular gauge.

Split the difference. 2.5 psi either way makes zero difference.

My Ram TPMS readings match my manual gauge exactly and that is true for my 2018 truck and formerly for my 2010. I would get a new gauge and recheck.

tpms vs tire gauge reading | Good Sam Community

rbp111
Explorer
Apr 18, 2019
Thanks for the input. I guess the TPMS is doing what it is supposed to be doing, i.e. note a change in tire pressure.
I guess I will leave it alone.
wilber1
Explorer
Apr 18, 2019
JKJavelin wrote:
What matters most in a TPMS is consistency and its ability to see the pressure drop is its main job. Use a good quality gauge for cold air pressure. When going down the road, watch for fairly consistent pressures and temperatures occasionally. The actual pressure itself on the TPMS is secondary as long as all tire readings are close to each other.
JK

I agree. I set the pressures with a gauge and rely on the TPMS to let me know if there is a big change. Pressures when running will change according ambient temperature, to how much weight a tire is carrying, which side of the rig is facing the sun etc.
Route_66_Travel
Explorer
Apr 17, 2019
I use a quality tire gauge to set all of my trailer tires to the same cold pressure, then monitor them with my TPMS system. Usually they are within a few pounds of the set pressures, unless they have been sitting in the sun for awhile. Once on the road the pressures vary from tire to tire just a bit, but never more than 3-5 pounds.
jkwilson
Explorer III
Apr 17, 2019
JKJavelin wrote:
What matters most in a TPMS is consistency and its ability to see the pressure drop is its main job. Use a good quality gauge for cold air pressure. When going down the road, watch for fairly consistent pressures and temperatures occasionally. The actual pressure itself on the TPMS is secondary as long as all tire readings are close to each other.
JK

Agree 100%. As an engineer, I was always concerned with accuracy, but in a lot of cases, repeatability is far more important and much, much less costly.
JKJavelin
Explorer III
Apr 17, 2019
What matters most in a TPMS is consistency and its ability to see the pressure drop is its main job. Use a good quality gauge for cold air pressure. When going down the road, watch for fairly consistent pressures and temperatures occasionally. The actual pressure itself on the TPMS is secondary as long as all tire readings are close to each other.
JK
Bobbo
Explorer II
Apr 17, 2019
My TPMS consistently reads 2 psi lower than my gauge. When reading the TPMS values, I just add 2 psi.
IdaD
Explorer
Apr 17, 2019
Grit dog wrote:
Split the difference. 2.5 psi either way makes zero difference.

Yeah as long as you're not way off it doesn't really matter. Tire pressures vary quite a bit from cold to rolling down the highway on a hot day, more than a couple of PSI.
Sam_Spade
Explorer
Apr 17, 2019
rbp111 wrote:
Or should I decrease the amount of air, putting the tpms as priority, in other words putting the psi to 110 down from the reading of 115?

Try another gauge.

But I think you will find that the gauge is "right" and the TPMS is off a bit.......or off more than the gauge.

TPMS sensors are really not intended to be used to "air up" the tires but to monitor them for pressure LOSS as you go down the road.
+- 5 PSI cold usually isn't a big deal.....and the pressure ALWAYS will go up as the tires heat up.

Once you get a feel for the calibration errors in the TPMS system, which can be different for each sensor, then you will know what readings are "normal".
bucky
Explorer II
Apr 17, 2019
You can buy 5 of the same exact gage or tpms sensor and get 5 different answers. Drives me crazy.
JimK-NY
Explorer II
Apr 17, 2019
My Ram TPMS readings match my manual gauge exactly and that is true for my 2018 truck and formerly for my 2010. I would get a new gauge and recheck.

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tpms vs tire gauge reading

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