How to calibrate 2025 4Runner OEM TPMS?

[MikeUtah]

I have come to learn that all four TPMSs (have not checked the spare) are reading 3 lbs. high. I have double-triple checked all four tires, with three different gauges, after sitting in a cool garage over night, and made sure the pressure was exactly 33 psi for all four tires. However, the multi-informational display shows all four tires at 36 psi. No TPMS warning lights have come on, as expected.

Can the TPMSs be calibrated?

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[MikeUtah]

Tire Pressures, TPMS Readings and Compressor Use – At Altitude

I previously posted that I thought my TPMS system needed calibrating. I was wrong! Being a Master scuba diver with extensive training in relative and absolute pressures, I should have immediately known better!

Situation: I live at 7,500 feet and noticed that my 2025 TH TPMS system readings are ~3.5 PSI lower than my reliable tire pressure gauge readings. When the truck was new, I assumed the TPMS readings were ‘correct’ and I over inflated my tires. To maintain the 33 PSI recommended for the OEM tires, I set the tire pressure to 33 PSI using a reliable tire gauge. The truck TPMS system will show readings of 30 PSI (TPMS rounds off to a whole number).

Yesterday I was off-roading and aired down my tires. Once back on pavement, I aired up my tires using the on-board compressor. I set the compressor to 33 PSI and aired up. I double checked the tire pressure using a reliable gauge. Guess what – the tire pressure was 36.5 PSI! Bottom line is that both the TPMS system and on-board compressor are ‘calibrated’ to sea level. Thus, from a practical point of view, in my situation at 7,500’ (MSL), I need to be aware that the TPMS system and on-board compressor will always read ~3.5 PSI ‘low’. To properly air up my tires to 33 PSI, I set the air compressor to 29.5 PSI.

Summary

• Vehicle at an altitude of 7,500’ (MSL)
• 33 PSI OEM tire recommended pressure (while not stated, pressure is to be determined by a gauge
• Actual tire pressures set by a gauge to 33 PSI (PSIG=pounds per square inch gauge)
• TPMS vehicle system – all tires reading 30 PSI (technically, PSIA=pounds per square inch ‘absolute’)
• If I need to air down to say 25 PSI - set compressor to 21.5 PSI (if using the compressor)
• If I need to air up to say 33 PSI - set compressor to 29.5 PSI

Definitions and References:

• PSI or pounds per square inch, is total pressure (a general or common pressure term).
• PSIG, or pounds per square inch gauge, is the difference between the pressure you’re measuring and the atmosphere’s ambient pressure. Think high altitude = lower atmosphere pressure.
• PSIA, or pounds per square inch absolute, is the difference between the pressure you’re measuring and the pressure at sea level. (Ok, for you technical folks, PSIA is technically the difference between the pressure you’re measuring and the pressure in a full vacuum, 0.0 PSIA. However, in the case of tire pressures, the starting point is 14.7 PSIA, pressure at sea level.
• For every 1,000 feet elevation change, pressure changes by about 0.48 PSI. In practical terms, that means at 7500’ MSL, the gauge pressure in a tire will read 33 PSI and the TPMS system will show 30 PSI (7500/1000=7.5x0.48=3.6, 33-3.6=29.4, rounded to 30 by TPMS)
• Need more science, there are many posts on sport car forums and TACO forums detailing the science.

 

[MikeUtah]

Tire Pressures, TPMS Readings and Compressor Use – At Altitude

I previously posted that I thought my TPMS system needed calibrating. I was wrong! Being a Master scuba diver with extensive training in relative and absolute pressures, I should have immediately known better!

Situation: I live at 7,500 feet and noticed that my 2025 TH TPMS system readings are ~3.5 PSI lower than my reliable tire pressure gauge readings. When the truck was new, I assumed the TPMS readings were ‘correct’ and I over inflated my tires. To maintain the 33 PSI recommended for the OEM tires, I set the tire pressure to 33 PSI using a reliable tire gauge. The truck TPMS system will show readings of 30 PSI (TPMS rounds off to a whole number).

Yesterday I was off-roading and aired down my tires. Once back on pavement, I aired up my tires using the on-board compressor. I set the compressor to 33 PSI and aired up. I double checked the tire pressure using a reliable gauge. Guess what – the tire pressure was 36.5 PSI! Bottom line is that both the TPMS system and on-board compressor are ‘calibrated’ to sea level. Thus, from a practical point of view, in my situation at 7,500’ (MSL), I need to be aware that the TPMS system and on-board compressor will always read ~3.5 PSI ‘low’. To properly air up my tires to 33 PSI, I set the air compressor to 29.5 PSI.

Summary

• Vehicle at an altitude of 7,500’ (MSL)
• 33 PSI OEM tire recommended pressure (while not stated, pressure is to be determined by a gauge
• Actual tire pressures set by a gauge to 33 PSI (PSIG=pounds per square inch gauge)
• TPMS vehicle system – all tires reading 30 PSI (technically, PSIA=pounds per square inch ‘absolute’)
• If I need to air down to say 25 PSI - set compressor to 21.5 PSI (if using the compressor)
• If I need to air up to say 33 PSI - set compressor to 29.5 PSI

Definitions and References:

• PSI or pounds per square inch, is total pressure (a general or common pressure term).
• PSIG, or pounds per square inch gauge, is the difference between the pressure you’re measuring and the atmosphere’s ambient pressure. Think high altitude = lower atmosphere pressure.
• PSIA, or pounds per square inch absolute, is the difference between the pressure you’re measuring and the pressure at sea level. (Ok, for you technical folks, PSIA is technically the difference between the pressure you’re measuring and the pressure in a full vacuum, 0.0 PSIA. However, in the case of tire pressures, the starting point is 14.7 PSIA, pressure at sea level.
• For every 1,000 feet elevation change, pressure changes by about 0.48 PSI. In practical terms, that means at 7500’ MSL, the gauge pressure in a tire will read 33 PSI and the TPMS system will show 30 PSI (7500/1000=7.5x0.48=3.6, 33-3.6=29.4, rounded to 30 by TPMS)
• Need more science, there are many posts on sport car forums and TACO forums detailing the science.

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