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Old 05-27-2016, 10:29 PM   #1
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TPMS

I'm looking for feedback on TPMS accuracy.

My TPMS seems to read about 4psi low.
Same error consistently on all four tires plus spare.
I compensate for it, but wish it weren't there.

The TPMS vendor, who seems honest, doesn't see the error at his location in California.

I've checked against several different gauges. All the gauges agree with each other and not with the TPMS.

The only thing that comes to mind is that I live at 6600ft elevation. Perhaps my TPMS doesn't properly compensate for altitude.
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Old 05-27-2016, 10:50 PM   #2
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Various TPM claim 3 to 5% accuracy. TPM is a monitoring and warning device and is not intended to be a substitute for a good quality digital hand gauge.

When tires are cool and at ambient (not driven for at least 2 hours and not in direct sun for at least 2 hours. Set all the tires to your Cold Inflation goal pressure based on your digital hand gauge.

You can look at your TPM Monitor after doing a "Signal reset" command or resetting the monitor so it registers the new cool temperature pressure. Now you know the monitor reading to expect.
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Old 05-27-2016, 11:02 PM   #3
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Recently bought a second digital pressure gauge as a backup just in case I lost or damaged the original one. The second gauge was 2 psi lower than the first. I took it back to Auto Zone and they let me exchange it for another unit. The new one was one lb over the first. I tried two mechanical gauges I've had for years and the results varied. Go figure!
My original digital gauge is never more than .5 psi different from the TSTM 507 sensors, so I'm happy with it.
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Old 05-27-2016, 11:13 PM   #4
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Quote:
Originally Posted by Tireman9 View Post
Various TPM claim 3 to 5% accuracy. TPM is a monitoring and warning device and is not intended to be a substitute for a good quality digital hand gauge.

When tires are cool and at ambient (not driven for at least 2 hours and not in direct sun for at least 2 hours. Set all the tires to your Cold Inflation goal pressure based on your digital hand gauge.

You can look at your TPM Monitor after doing a "Signal reset" command or resetting the monitor so it registers the new cool temperature pressure. Now you know the monitor reading to expect.
Agreed on when and how to set cold inflation levels.

My TPMS claims +/-1.5psi accuracy, which is comparable to the spec on my AccuTire digital gauge. Based on comparison on multiple tires using a variety of gauges, my Accutire gauge reads correctly and the TPMS is low by 4psi. Kinda disappointing.

Despite the error, it's fun to be driving along and notice that the right side tires are at higher pressure than the left, and then realize that the sun is on the right and is warming those tires.

I also noticed that here in Colorado where there can be a wide temperature swing during the day, if I set my tire pressure early in the morning when it's still cold, pressure when towing at 2pm in the afternoon warmth can be surprisingly high. Tires set at 65psi cold may be running at 75psi warm, which is getting close to the 80psi rating of my wheels.
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Old 05-28-2016, 12:06 AM   #5
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Sunseeker 3010 running TST 507s internally mounted on metal bands. After 5 camping trips, the Passenger side inside dual runs consistently 5 degrees warmer. Cold pressure is exactly the same on the pair. Wanna guess which side the exhaust is on? It's nice to know the digital temp, but the little things like this can bug you until you get to the A'ha! moment.
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Old 05-28-2016, 09:43 AM   #6
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Originally Posted by Gidyupgo View Post
Sunseeker 3010 running TST 507s internally mounted on metal bands. After 5 camping trips, the Passenger side inside dual runs consistently 5 degrees warmer. Cold pressure is exactly the same on the pair. Wanna guess which side the exhaust is on? It's nice to know the digital temp, but the little things like this can bug you until you get to the A'ha! moment.
That would have driven me nuts.
Nice sleuthing!

Have you checked the accuracy of your TSTs?
If so do you know the altitude where you checked?
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Old 05-28-2016, 12:06 PM   #7
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Quote:
Originally Posted by Gyrogearloose View Post
Agreed on when and how to set cold inflation levels.

My TPMS claims +/-1.5psi accuracy, which is comparable to the spec on my AccuTire digital gauge. Based on comparison on multiple tires using a variety of gauges, my Accutire gauge reads correctly and the TPMS is low by 4psi. Kinda disappointing.

Despite the error, it's fun to be driving along and notice that the right side tires are at higher pressure than the left, and then realize that the sun is on the right and is warming those tires.

I also noticed that here in Colorado where there can be a wide temperature swing during the day, if I set my tire pressure early in the morning when it's still cold, pressure when towing at 2pm in the afternoon warmth can be surprisingly high. Tires set at 65psi cold may be running at 75psi warm, which is getting close to the 80psi rating of my wheels.
Pressures for setting tires or wheel limits are based on "cold" tires.

"Cold" tire means not warmed up by Sun or driving. It does not mean you have to put the tires in the fridge.

Tire pressure will increase by about 2% for each 10°F. Here is the Engineering info with links to even more details for those interested in understanding the "why".
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Old 05-28-2016, 12:17 PM   #8
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On my blog I have a number of posts on Temperature and Pressure and even on Elevation effects.

Also some information on how to have, use and preserve your own "Master" gauge.

I suggest you start HERE.

Then if you want or need more details simply look at index on left. I am not allowed to simply re-post my blog writings here.

FYI I use Accutire Tire MS4120 from Amazon for about $10. I have checked three of these againsed certified ISO Laboratory master gauges and the Accutire units were always +/- 0.5 psi

You might also read "Measurable vs Meaningful"
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Old 05-28-2016, 03:22 PM   #9
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You just have to choose which guage you want to believe when you set your cold pressure. I believe the digital guage I've been using for years. Compared to that, my TPMS reads 2psi low consistently across all tires and I've just gotten used to that.

The point of a TPMS is not necessarily to be able to tell your absolute pressure, its to be able to monitor for unexplainable relative differences, especially sudden changes (which should trigger an alarm anyway). The initial conditions, once I know they have been properly set, are not important to me.
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Old 05-28-2016, 03:25 PM   #10
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Originally Posted by DaveSchwartz View Post
You just have to choose which guage you want to believe when you set your cold pressure. I believe the digital guage I've been using for years. Compared to that, my TPMS reads 2psi low consistently across all tires and I've just gotten used to that.

The point of a TPMS is not necessarily to be able to tell your absolute pressure, its to be able to monitor for unexplainable relative differences, especially sudden changes (which should trigger an alarm anyway). The initial conditions, once I know they have been properly set, are not important to me.

X2
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