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TPMS vs. My Tire Gauge

  • + 5 or higher

    Votes: 2 2.2%
  • + 4

    Votes: 3 3.2%
  • + 3

    Votes: 2 2.2%
  • + 2

    Votes: 1 1.1%
  • + 1

    Votes: 2 2.2%
  • Very Accurate

    Votes: 16 17.2%
  • - 1

    Votes: 5 5.4%
  • - 2

    Votes: 27 29.0%
  • - 3

    Votes: 25 26.9%
  • - 4

    Votes: 3 3.2%
  • - 5 or lower

    Votes: 7 7.5%
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Discussion Starter #1 (Edited)
Been doing research in the forum. Like everyone else, my TMPS reads differently than my tire pressure gauge. I just wanted to do a poll with other TPMS owners to see what kind of readings they are getting compared to their gauge. Please indicate your TPMS reading. My TPMS reads -2 lower than my gauge.
 

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Depends on the conditions. At 68 degrees/my altitude it is always the same and at other temps and barometric pressures it can be different. Seems very difficult for people to get their minds around that.
 

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Mine reading cold is usually + 1/2lbs off on the high side, don't check it a whole lot against my guage but when I do that's what I see.
 

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This is a good poll. Interesting to see I'm in line with all the majority of people who's TPMS reads 3 psi lower.
 

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I just wanted to do a poll with other TPMS owners to see what kind of readings they are getting compared to their gauge.
And how do you know your gauge is right? :confused:

I have one particular gauge that I use for my cars. That gauge and the TPMS are pretty close if the temp is around 68°.
 

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Discussion Starter #6
I'm not saying my gauge is right. I just wanted to know other results. Seems that the majority results is -3 from what I have read in the forums. This poll is just a visual in case others wanted to know just like myself.
 

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"The TPMS system reads the pressure from inside the tire and is not impacted by environmental conditions therefore those readings may be significantly different from those of some tire gauges especially if the gauge is also not accurate or environmental conditions have changed." There are gauges that advertise they are not effected by temps, changes in altitude and humidity and they are best to compare with. So until we get the type of gauge used, the temperature at measurement, the altitude and barometric pressure impacting the gauge from each person polled we don't have a lot more knowledge. Most gauges or off by about +/- three pounds.

Hawc I didn't know Blue Point made a tire gauge that could be calibrated. Is it oil filled? What model # is it?
 

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"The TPMS system reads the pressure from inside the tire and is not impacted by environmental conditions therefore those readings may be significantly different from those of some tire gauges especially if the gauge is also not accurate or environmental conditions have changed." There are gauges that advertise they are not effected by temps, changes in altitude and humidity and they are best to compare with. So until we get the type of gauge used, the temperature at measurement, the altitude and barometric pressure impacting the gauge from each person polled we don't have a lot more knowledge. Most gauges or off by about +/- three pounds.

Hawc I didn't know Blue Point made a tire gauge that could be calibrated. Is it oil filled? What model # is it?

They all read pressure from the inside. That's where the pressure is. DOH! Heat your tires up and the pressure goes up with TPMS or a regular gage.
 

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Most tire pressure gauges measure the ambient pressure outside the tire. TPMS measures pressure from within. The OEM manufacturer had a good explanation of the difference on their site at one time. Of course TPMS changes with temps but usually the difference between the two completely different measurement systems being discussed stays the same.

It is possible that the threshold alarm is set conservatively for Porsche's TPMS.
 

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Most tire pressure gauges measure the ambient pressure outside the tire...

SF:

Most tire pressure gages measure the ambient pressure outside the tire? Really?

Here's my take. SOME digital tire gages zero out to ambient air pressure (barometric pressure) before they take a tire pressure reading. I have two types of digital gages at home that do this. Analog gages that I've seen and owned do not have this function. One of my digitals goes through a short setup zeroing procedure before each measurement before it can be put on the gage (annoying) and the other has a "Zero" button on it that simply measures barometric pressure and calls it "Zero" when you push the button.

This is something TPMS cannot do unless the tire is deflated. So, if the sensor was zeroed and then mounted at sea level (assuming there is some way to zero them) and the tire pressures were being measured in Denver, there might be an issue here. My car is from New Jersey, travelled to Savannah, GA and then moved to Chicago, 610 ft above sea level. I had the TPMS monitors rebuilt here when I put my new tires on the rims two months ago. This did nothing to change the readings which are still about 3psi low on the TPMS.

I'm chalking this up to just plain innacuracy of the often spinning, pothole hitting, battery powered, heated and cooled, lightweight, radio transmitting little plastic sensor inside the tire. They just aren't accurate enough to fill your tires by and they're exposed to too many hostile forces and constraints. It's amazing to me that they work at all.

HOWEVER.... ALL tire gages measure the pressure INSIDE the tire. That's why they have that little valve thingie on the rim,....so you can measure and change, at will, the "ambient" pressure inside the tire without actually being inside the tire.

The OEM manufacturer is doing something Porsche and a lot of other German manufacturers do very well. Make far flung technical points, valid or not, to explain why there stuff doesn't work right yet. Sounds much better than "We're working on it".

Please read carefully the Turbo Encabulator Article in Articles section. :cheers:
 

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We may be talking alike. Gauge pressure is the difference between the absolute and ambient pressures and the relationship can be expressed as Pg = Pa - Pambient

psia is the unit "pounds per square inch absolute, and psig is "pounds per square inch gauge.

We do agree to use a good gauge for filling and checking tire pressure and TPMS as a warning device. An example is at sea-level the ambient pressure is 14.7 psia, while in Denver at 5000 feet the ambient pressure drops to about 12.2 psia. Thus, a person at 5000 feet who adds or removes air from a tire to a pressure of 30 psig according to the person's gauge will resultin a tire with an absolute pressure as measured by a tire sensor placed within the tire that is about 2.5 psia less than what a person at sea level.
 

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Is it possible that TPMS is using absolute pressure transducers? Unless I'm mistaken the DME system measures ambient pressure so they would have a reference to correct to guage pressure.

Either way I think the system is overengineered and overcomplicated for it's purpose. A low tire pressure alarm. Temperature compensation and all the rest seems a bit much when all it needs to tell me is the tire is going flat.
 

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Les, you might like the TPMS in my Audi. You fill the tires with any pressure you choose, tell the computer that is what you want to measure against and it warns you if falls below that by some internal pre-determined threshold percentage (guided by government regs). Gives you no feedback, no current pressures, zip nada until the warning sounds.
 

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Perfect. What else could you ask for in a warning system? And it would negate the need for the endless debate on the accuracy or lack thereof in the TPMS.
 

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This is a very good thread. However, I can not answer the poll as written. Why? Because there are so many variables and offering a third axis including the +/- option would be more accurate--at least for me and my Cayenne Turbo.

I have had a lot of trouble with TPMS which was an option on my 2005 but I would not want to live without it.

My service manager in Scottsdale was excellent. He advised me that there are three (3) TPMS systems on my Cayenne and he suggest that I go with the one that gave me pressure warnings in red on start up because it took into account the load, temperature, altitude and humidity. He also suggested I feel free to overfill by about 2 pounds.

Lord knows I spent a lot of time trying to adjust the pressure for the perfect settings but with an air compressor onboard I was able to provide my own air on the Alcan when the stations had all taken their air hoses inside for the winter.

These are nice cars! Certainly over engineered but perfectly so. I trust the car to warn me on start up of what it needs and I trust the TPMS systems on my SUV more than my old hand guage.
 

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Yes. Over many years and cars and tires and gauges.
OK, then how come I can't find a dial-type or digital gauge that isn't accurate to within 1 PSI at 32 PSI? I have four now, two digital, two mechanical, including one el-cheapo plastic thing, and they all read the same. If your statement is true, the chances of that happening is near zero.
 
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