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So I decided to check my tires with a precision gauge and I am glad I did. All of my tires were ~3 to 4 lbs lower than my monitor was reporting. I inflated them all to ~40 lbs (max is 44). My front right read ~ 39 so it was slightly lower that all the rest. I got in my car and it was reporting 42 on the ones that had 40 and it reported 43 on the one that had 39.

Has anyone else seen similar discrepancy? Might be work checking on.
 

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So I decided to check my tires with a precision gauge and I am glad I did. All of my tires were ~3 to 4 lbs lower than my monitor was reporting. I inflated them all to ~40 lbs (max is 44). My front right read ~ 39 so it was slightly lower that all the rest. I got in my car and it was reporting 42 on the ones that had 40 and it reported 43 on the one that had 39.

Has anyone else seen similar discrepancy? Might be work checking on.
I have always checked my TPMS values from the driver's seat. (Both cold and warm pressures.) I have read here on the Forum, that the left front tire may read slightly higher due to a change in balance by the driver's seat being occupied and more weight on the LF tire. I always (by definition) check gauge pressures at the valve stem, with the car empty. How does the addition (and distribution) of an extra 200 pounds in the car show up in TPMS indications? The surface area of each tire does not change much, but there is 50 more pounds being held up by each tire. This must affect indicated tire pressures, doesn't it?
 

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Has anyone else seen similar discrepancy? Might be work checking on.
This is our first car with tire pressure sensors, so I don't know how normal it is. They do seem to be all over the place. I set my tire pressure with a stick gauge. With all tires set to 40 psi, cold, the sensors vary by plus or minus 2 pounds. Once up to temperature, they all match within 1 pound, at a higher pressure, of course. This behavior repeats each time they cool down, and heat up. I don't know why they would be more consistent when warm.
 

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For me the big problem is high altitude. In my conversation with GM engineers they seemed surprised when I told them the sensor was way off, because it subtracts ambient air pressure and assumes that that is 14.7 psi, making no accommodation for the fact that it is 12 in Denver and 10 up here. Hence the readings are quite wrong. My Highlander had the same problem but the dealer told me how to reset. There is no such reset in Chev. calls. The engineers seemed to realize that this is an important problem that should be fixed (unlike their response to my other concerns). Anyway, the sensors on the screen read 34 when there is 38 lbs of pressure in the tires.
 

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I have had quite a few cars with TPMS, I haven't seen one yet that would agree with my good tire pressure gauge.

Just like every gauge its only an estimate of what it is monitoring.

The best that you can do is figure out how much they are off, then add air when needed.
 

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Great thread guys. Currently trying to manage a 3lb spread on the tpms when the (admittedly old) hand guage says even.


Edit: now within 1lb. Happiness.
 

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If you set the tire pressure cold and in the dark, you would see them change when the sun
came up. The sun will heat tires and raise pressure. If the sun is only hitting on one or both
tires on one side of the car, the side in the shade will be lower. As you drive and all the tires
come up to temperature, they'll balance out.

They'll match again because all tires are now at an even temperature, unless the sun is causing
one side to be hotter based on sun load. As far as pressure VS gauge VS altitude, it's
simple. The gauge is exposed to it's environment/barometric pressure. The TPMS is not.
The tire is also affected by the barometric pressure differential.
The gauge is compensating for the barometric value. Not TPMS sensor.

You can buy 5 gauge's and they'll all show a different reading. When setting tire pressures,
I use a digital gauge, but, I use the TMPS as the proper indication of my tires actual pressure.

YMMV!

I trust the TPMS to give a more accurate reading, but I always make sure it's close with a gauge.
I run 50 PSI in my tires. I ran 55 in my C-Max Energi, but it had a higher rated tire.
 

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...I set my tire pressure with a stick gauge. With all tires set to 40 psi, cold, the sensors vary by plus or minus 2 pounds....
Stick-type gauges are notoriously inaccurate, because they become "sticky", and the friction on the stick varies over time, dirt and wear. Dial-type gauges are more likely to be accurate, or at least consistent.
 

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Stick-type gauges are notoriously inaccurate, because they become "sticky", and the friction on the stick varies over time, which affects their accuracy. Dial-type gauges are more likely to be accurate, or at least consistent.



At least until it gets dropped :eek: This is why, I use a good digital gauge :nerd:
 

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Stick-type gauges are notoriously inaccurate, because they become "sticky", and the friction on the stick varies over time, dirt and wear. Dial-type gauges are more likely to be accurate, or at least consistent.
I've checked them with two different dial gauges on my air compressor, and several different dial bicycle pumps. The tire pressure sensors are the ones that are not consistent.
 

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I've checked them with two different dial gauges on my air compressor, and several different dial bicycle pumps. The tire pressure sensors are the ones that are not consistent.

Tire pressures change with temperature. The sun will change a tires pressure from heat.
Tires heat up when driven. The biggest cause of change is the sun hitting 1 or 2 tires at a time.
 

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Tire pressures change with temperature. The sun will change a tires pressure from heat.
Tires heat up when driven. The biggest cause of change is the sun hitting 1 or 2 tires at a time.
Yup. I see that too. I am talking about the car sitting in a garage overnight. The next day the readings are all over the place with cold tires. Once warmed up they fall right into line.
 

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Yup. I see that too. I am talking about the car sitting in a garage overnight. The next day the readings are all over the place with cold tires. Once warmed up they fall right into line.
Yeah, that's been my experience too. I'm kind of wondering if maybe they go into some sort of power-down mode when they've been sitting without being interrogated for a while.
 

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Yeah, that's been my experience too. I'm kind of wondering if maybe they go into some sort of power-down mode when they've been sitting without being interrogated for a while.
Yes, they do go to sleep to save battery power.
 

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Yes, they do go to sleep to save battery power.
About the batteries... If you leave the instrument cluster set to always show the tire pressure, would it run the batteries down prematurely? Or are the TPMS designed to report at a particular sample rate independent of the car?
 

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I check tire inflation once a month and set all four tires to the recommended 38 psi using an accurate dial gauge.

When my car is sitting in the garage and tires are cold TPMS pressure sensors read +/- 1 psi of 38. That tells me the TPMS readings are pretty accurate.

Only exception would be when there’s a large change in ambient temperature, every 10 degree change would add or subtract about 1psi.

I never see the large TPMS sensor reading swings some are reporting.
 

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Back in my racing days the right air pressure was critical, the guy who owned the race car came up with a high quality furnace dial gauge it only measured up to 50 lbs.

A few brass fittings and a hose was adapted to it to work at that time.

We were only interested in air pressure below 50 lbs, the slicks only ran with 13 lbs of air to get the best traction.

You can buy a cheap dial style air gauge to get all the fittings needed, then just buy the good pressure gauge at a furnace supply house to make your own high quality air pressure gauge.
 

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You know, a man with two watches never knows what time it is... ;) A couple of pounds here and there is pretty much what the weather does every day. Temperature goes up, pressure goes up. Temperature drops, pressure drops. And then then there is barometric pressure. You could chase your tires every day.
 
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