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Discussion Starter · #1 ·
I had a problem with a punctured tire (which was repaired) and have been doing a bunch of manual tire pressure measurements -- at first making sure the tire would hold air enough to get it fixed, and then after to make sure the fix doesn't leak.

Anyway, throughout all of this I've noticed that the TPMS display isn't completely matching what my tire gauge says. When I got the car, the salesman explained during delivery that it takes a few minutes for the sensors to display info.

My tires are all inflated to ~38 PSI cold on my manual gauge. When the TPMS display first comes up, they start out at about 34 and go up to about 37 over time when driving. Generally a bump in pressure is expected over time due to heating, but if the increase in pressure on the TPMS is accounted for by heating, it would mean it's starting out about 4 PSI low.

I'm guessing this display is mostly meant for reference purposes, not lab-grade accuracy. My last car had TPMS warnings, but not pressure, which was a PITA if it went off as it meant screwing around with all the tires.

Anyway, I'm going to be watching this display more closely to see if I have any leak problems with the repaired tire. I hate to drive on repaired tires, but I have just under 6k miles on my Limited and would rather not be buying 2 or even 4 new tires.
 

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I'm guessing this display is mostly meant for reference purposes, not lab-grade accuracy.
I think this is key.

The same can be said for your (or mine, for that matter :)) handheld gauge(s) as well.

I'm a benchtop academic scientist by trade and training, so, yeah, I feel your pain! :D

I don't worry about it too much. As long as they're in the ballpark, I'm not sweating it.

It's always funny to look at the display during a long drive, particularly if only one side of the car getting all the sun. ;)
 

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i have 3 digital gauges and all 3 with in -+0.2 PSI of TPMS sensors (on both Subaru's and 1 2008 GM car)

example..
if i set pressure based on gauge 35.7 on all 4 direct reading of sensor will be 35.7+-0.2 and car will show 36 on all 4
 

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also need to remember sensor in the car is based on Relative or sea level pressure and most handheld gauge self reset on "power up" based on Absolute barometric pressure (atmospheric air pressure at a particular location)
 

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Discussion Starter · #5 ·
i have 3 digital gauges and all 3 with in -+0.2 PSI of TPMS sensors (on both Subaru's and 1 2008 GM car)

example..
if i set pressure based on gauge 35.7 on all 4 direct reading of sensor will be 35.7+-0.2 and car will show 36 on all 4
Interesting, because both my analog gauges (totally different make) are within 1 PSI of each other and 3-4 PSI off the car. I'm kind of tempted to buy a third digital gauge because they're cheap and see what it reads, but finding one that's truly accurate is the kicker.
 
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