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Friday, May 28, 2021

Does your TPMS "control" you? or can you control it?

I saw a post on an RV Forum about a tire "Blowout" on an RV that had a TPMS.

The RV owner said they had TPMS but still had a sidewall failure. He also said, he "set his  "baseline" PSI which is the threshold for the low end pressure reading and then the upper limit alarm will tell you if you''re exceeding normal pressures and headed for a blowout. Same thing for the temperatures as well....set the baseline and then it alerts you if the tire temperature is above normal and too high. I used my unit last year on 2 long haul trips to MI and it performed well. Gave me the piece of mind knowing I could keep an eye on the tire pressures and temps. I do recommend the unit. I purchased the unit which can support up to 22 sensors, but got the TPMS system with 6 sensors on Amazon, then bought 2 additional sensors for a total of 8 - 4 for my TV and another 4 for my TT. My trailer has dual axles. I mounted the wifi extender on the front of my TT just behind the battery box and use the clip on leads from the battery to power it. The wifi unit is in my truck and I tuck it in the center pocket in my cab. Works well."

I pointed out that not all TPMS let you set that actual low pressure warning level. Some use a % or number of PSI below the "set pressure" AKA Baseline. Others let you set the low pressure warning level.

I recommend that the low pressure warning level be no lower than 5 psi below the minimum pressure needed to support the measured load on the inflation for the tires on that axle. With some TPMS, this will require some extra calculation and work as you will need to set the Baseline higher than your actual "cold" inflation.

If Tire minimum inflation needed to support the measured load was 70  your low warning level should be no lower than 65.
If your system has the warning at -25% from "baseline" then you need to set your Baseline to 87 psi  (75% of 87 = 65). Some systems use the pressure in the tire when you first connect the TPM sensor as the "baseline" so you would need to pump up your tires to 87 before first connecting the TPM sensor. Once the TPM system is fully connected you could then lower your 87 to  80 (70x 1.15).
The 1.15 is a suggested margin of inflation so you are not pumping up your tires if the Ambient temperature drops. Remember that a drop of 10°F will result in about a 2% drop in the "cold" tire pressure.
Yes this is complex but that is a problem with the TPMS MFG not giving the user full control of your warning and baseline inflation levels. Please learn how your TPMS is programed. Your instructions should tell you how to set the "Low Pressure Warning Level" but if it doesn't you will need to do the above math.

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