TPMS vs hand gauge

[bass mechanic]

Huh? External pressure gauges read GAUGE pressure which is the amount in addition to atmospheric pressure. That won't be a 3 psi difference from an absolute gauge, it would be 14.7 psi difference.

 

The TPMS is reading gauge pressure just like a manual pressure gauge does. Any difference you are getting is the difference between two separate pressure gauges'readings. And having a difference doesn't necessarily mean either gauge is correct or calibrated...

No your wrong, tpms has no way of referencing atmospheric pressure because it's inside the tire. It's internal pressure sensor is calibrated at 0 in a vacuum. At sea level or approximately 14.7 psi it is actually reading 14.7 but the electronics are programmed to zero that reading as reference.

When you fill the tire to 30 psi it reads 30 psi as you would expect

 

A mechanical tire gauge can only read the difference between inside pressure and outside pressure, and if you lower the outside pressure without changing the inside pressure your gauge will read 3 psi more than is actually in the tire at 6500 feet. Trust me I've lived here all my life! And I also fly airplanes. Getting a pilots license requires a pretty accurate understanding of thinks like barometric pressure, pressure altitude and density altitude, relative pressure and so on.

 

You believe what you want, but ask yourself what a tire pressure might read at 32 psi if you placed a tire gauge on it in the vacuum of space. I can assure you it won't read 32 psi. It would actually read 32+ 14.7+ 14.7

 

 

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[spectaculous]

No your wrong, tpms has no way of referencing atmospheric pressure because it's inside the tire. It's internal pressure sensor is calibrated at 0 in a vacuum. At sea level or approximately 14.7 psi it is actually reading 14.7 but the electronics are programmed to zero that reading as reference.

When you fill the tire to 30 psi it reads 30 psi as you would expect

 

A mechanical tire gauge can only read the difference between inside pressure and outside pressure, and if you lower the outside pressure without changing the inside pressure your gauge will read 3 psi more than is actually in the tire at 6500 feet. Trust me I've lived here all my life! And I also fly airplanes. Getting a pilots license requires a pretty accurate understanding of thinks like barometric pressure, pressure altitude and density altitude, relative pressure and so on.

 

You believe what you want, but ask yourself what a tire pressure might read at 32 psi if you placed a tire gauge on it in the vacuum of space. I can assure you it won't read 32 psi. It would actually read 32+ 14.7+ 14.7

 

 

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I stand corrected. Sort of.

 

I didn't think about elevation, since in Houston, we are practically at sea level.

 

I was assuming that the sensors were actually measuring a dp since they physically could (the valve stem connected to them could easily provide atmospheric pressure).

 

But I honestly do not know what technology they actually employ, so I'll take your word that they are calibrated to a perfect vacuum.

[silverplate]

Always a match between TPMS and my gauge. Quality of the gauge could be the difference.

[Retired Bob]

I finally got by the dealer - only 2 miles from the house so the tires were fairly cool. The tech used what he said was a 1 month old $150 digital gauge that they use in the shop (it was a handheld but pretty large in size). We agreed to set the tires to 33psi. As he set each tire to 33psi, I used my gauge and in every case I showed 35psi while the TPMS showed 33/34. So I just marked my gauge storage case with "Reads 2# high). The next morning at 6am and w/o driving, the TPMS read 32psi all around and that's how it will stay for the moment.

 

At least my gauge reading was consistent, just 2 lbs high.