TPMS accurate?

[Big Dog]

I have a Model 3 with 19" sport wheels, so my target pressure is 42 psi (per door jamb). I have checked with two analog pressure gauges and both show 42 per tire cold. But after I roll two blocks down the street, the video screen shows 44 psi all around.

Is two pounds within normal range? Or, do I need a new manual gauge?

fwiw: bought the following gauge on amazon.

https://www.amazon.com/Vondior-Pres...st.&sr=8-1&store_ref=SB_A02929562QU55NXO2R0QS

 

[Magnets!]

Tire pressure increases when tires warm up. 2 lbs in 2 blocks sounds like more than normal though. My TPMS matches my hand gauge.

 

[Dr. J]

I inflate my tires to all the same PSI (44.5 or 45.0, the max per my door sticker) and one sensor always reads lower than the other three. I figure that sensor is a bit off.

 

[coleAK]

A high quality gauge is always more accurate than TPMS sensors.

 

[JackAttack]

I am 5280’ up in Denver. Hand gauge 4-5 psi higher than tpms. I had to “teach” system that 38 is normal. Does this make sense for altitude difference? Have M3P about 3 weeks old.

 

[Need]

I have an air pump with digital gauge. It matches exactly the same as the tires TPMs readings. One of my tire has a slow leak. I have to pump it up a few PSI every 2 weeks. Going up 2 PSI for 2 blocks seem fast.... usually it goes up about 2 PSI for 10 miles on the freeway.. and then it will stop around 3 to 4 PSI above the cold pressure even after 2 hours of driving.

 

[mongo]

I am 5280’ up in Denver. Hand gauge 4-5 psi higher than tpms. I had to “teach” system that 38 is normal. Does this make sense for altitude difference? Have M3P about 3 weeks old.

How did you do that? There is a whole thread on the altitude compensation issue. Denver is 2.5 psi less that sea level.

 

[coleAK]

I am 5280’ up in Denver. Hand gauge 4-5 psi higher than tpms. I had to “teach” system that 38 is normal. Does this make sense for altitude difference? Have M3P about 3 weeks old.

Psi is psi regardless of altitude. A TPMS or gauge dosnt know what altitude it’s at nd it dosnt matter. In a sealed container like a tire, As altitude increases so does PSI. So in Denver with decreased air density your PSI of 45 on the TPMS would equal 45 on a gauge.

 

[mongo]

Psi is psi regardless of altitude. A TPMS or gauge dosnt know what altitude it’s at nd it dosnt matter. In a sealed container like a tire, As altitude increases so does PSI. So in Denver with decreased air density your PSI of 45 on the TPMS would equal 45 on a gauge.

TPMS sensors operate on absolute pressure. Gauges operate on differential pressure. Tires operate on differential pressure.
30 psi on a gauge at sea level is really 44.7 psi absolute, in Denver, it is 44.7 absolute, but 32.5 psi gauge. In a vacuum, it would be 44.7 psi and gauge.
On ICE cars, the computer reads the manifold absolute pressure (MAP) sensor when the car is not running to calculate the ambient pressure offset.

 

[coleAK]

TPMS sensors operate on absolute pressure. Gauges operate on differential pressure. Tires operate on differential pressure.
30 psi on a gauge at sea level is really 44.7 psi absolute, in Denver, it is 44.7 absolute, but 32.5 psi gauge. In a vacuum, it would be 44.7 psi and gauge.
On ICE cars, the computer reads the manifold absolute pressure (MAP) sensor when the car is not running to calculate the ambient pressure offset.

I grew up in Tahoe. My last house there was at ~7300 ft, I never had problems with my MB TPMS but I’ll admit I left there for good in 2003. But looks like things are different now, I stand corrected. I regularly have my current Land Cruiser from PSI set at sea level up to 5-6k feet and don’t get TPMS alarms. I’ll admit though I have on board air and I “air down” most times I’m up that high as I’m off road so I’m checking it with a gauge.

We used to lower the tire pressure on the Humvees before takeoff on long distance transport due to the altitude change. They had CTIS so it was easy. Also I’m pretty sure they measured off a pressure differential not absolute.

 

[mongo]

I grew up in Tahoe. My last house there was at ~7300 ft, I never had problems with my MB TPMS but I’ll admit I left there for good in 2003. But looks like things are different now, I stand corrected. I regularly have my current Land Cruiser from PSI set at sea level up to 5-6k feet and don’t get TPMS alarms. I’ll admit though I have on board air and I “air down” most times I’m up that high as I’m off road so I’m checking it with a gauge.

We used to lower the tire pressure on the Humvees before takeoff on long distance transport due to the altitude change. They had CTIS so it was easy. Also I’m pretty sure they measured off a pressure differential not absolute.

CTIS was likely gauge pressure for read back and control. Absolute wasn't a thing until self contained in tire pressure sensors, since the was no longer a reference.
One of the Falcon 1 rockets was damaged during descent on the flight to the launch site due to cabin repressurization.