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So, some of you may have seen my posts about setting tire pressures and my continual complaints that the TPMS system on the dash is consistently 2-3 psi lower than any handheld gauge I use.
It turns out that the onboard TPMS system is calibrated for sea level. I guess it measures absolute pressure inside the tire and subtracts 1 Bar or 14.7 psi.
A handheld gauge is repeatedly zeroed at the ambient pressure where I live (Denver at 5,280 feet elevation which is only 0.8252 Bar or 12.13 psi ambient pressure) and displays the tire's pressure margin above that baseline. So, if I am aiming for 32 psi hot pressures here as recommended by the tire manufacturer, then I have to aim for around 29-30 psi on the TPMS on the dash.
And if the owner's manual says for the Performance pressure settings I should aim for 27 psi front and 30 psi rear pressures when cold, I want the dashboard to show something closer to 24-25 psi front and 27-28 psi rear (but my handheld will show the expected 27 psi front and 30 psi, rear). This has been a head-scratcher for years and I've unfairly blamed the TPMS for being unreasonably inaccurate (and always reading too low).
I thought the TPMS system zeroed itself at the altitude the car is at. Doesnt make sense that its only zeroed and accurate at sea level.
In my case I'm at 720ft and what I set my tires at on either of my P cars is accurately reflected on my cars TPMS readings...(also accurate on my Honda)
I thought the TPMS system zeroed itself at the altitude the car is at. Doesnt make sense that its only zeroed and accurate at sea level.
In my case I'm at 720ft and what I set my tires at on either of my P cars is accurately reflected on my cars TPMS readings...(also accurate on my Honda)
Nope - it can’t possibly zero itself for changing altitude, because the TPMS sensor is sealed inside the tire and has no access to the outside ambient pressure.
720 ft is very little and represents a small fraction of 1 psi difference (that’s why you don’t experience any inaccuracy). You won’t see a difference of 1 psi until you reach about 2,000 ft of elevation.
If it was inaccurate at different altitudes that would be expressed in the owners manual, don't u think?
I haven’t read the entire manual carefully, so I don’t know if it addresses this or not.
If you don’t believe me, take a mountain road trip (to a high mountain pass) with your favorite handheld digital pressure gauge (that zeroes on turn-on) and compare again to TPMS dashboard reading.
If it was inaccurate at different altitudes that would be expressed in the owners manual, don't u think? 720 is 13% of 5280...not exactly a small fraction...
Try using the calculator to which I linked. 720 feet is only going to change air pressure by 0.38 psi. The TPMS system only has a full PSI of resolution (no decimal), so it is effectively not a very significant change.
11-05-2023, 02:32 PM
Setting Tire Pressure at High Altitude
