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Old 10-19-2020, 06:10 AM #1
SilverFox2020 SilverFox2020 is offline
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TPMS accuracy?

The other day I was prepping my 2020 for a 500 mile trip. I needed to add a few pounds of air to my tires according to my TPMS, so I did. Here is the thing... I have a high end tire gauge that reads in half pound increments that I use on my motorcycle. I filled my tires to 35psi exactly. When I checked what the TPMS it showed that only on tire was 35psi one was 37psi and two were 33psi. Why the difference? Does the TPMS read accurate pressure or is it just a guideline?
I have the stock Duelers with 12000 miles on them and no fix a flat or anything like that in any tires.
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Old 10-19-2020, 07:37 AM #2
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This is common, you are seeing the manufacturing spec variance or component tolerance. While some newer systems are getting close, they can still have a pound or so of variance. I don't know about the Toyota system, but some can be calibrated by the dealer once the pressure in the tires is matched with a known gauge. Hopefully someone here will know.

Originally, these systems were never intended for for measurement. They were solely for warning the driver to inspect the tires.

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Old 10-19-2020, 09:17 AM #3
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I use this and it always matches the TPMS

TPMS accuracy?-1-jpg
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Old 10-19-2020, 09:36 AM #4
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TPMS accuracy?

Strange that yours were that far off. My Longacre analog gauge reads within 1 PSI of the TPMS. All show within 1 PSI of each other when driving as well. However sometimes when the car sits in the sun in certain ways some of the tires may heat up and gain pressure more than the others. Is it possible thatís what happened in your case? Maybe the sun was beating down on that 37 PSI tire and not the others?

Remember also to measure pressure when the tires are cold. They will gain several PSI during driving especially on the highway. Additionally sometimes using a tire pump that gets quite hot may cause some pressure drop in a tire if it was the last one you filled (when the pump got hot filling the others before it) as the air cools back off. I notice this when airing up after off-roading. The pump gets hot and I need to add a bit more air to the 3rd and 4th tire to compensate for the added temp of the air going in through the hot pump. Once the air cools back off those 3rd and 4th tires tend to be a little lower than the first two if I fill to the same PSI.

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Old 10-19-2020, 10:36 AM #5
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Quote:
Originally Posted by rightyouareken View Post
Strange that yours were that far off. My Longacre analog gauge reads within 1 PSI of the TPMS. All show within 1 PSI of each other when driving as well. However sometimes when the car sits in the sun in certain ways some of the tires may heat up and gain pressure more than the others. Is it possible thatís what happened in your case? Maybe the sun was beating down on that 37 PSI tire and not the others?

Remember also to measure pressure when the tires are cold. They will gain several PSI during driving especially on the highway. Additionally sometimes using a tire pump that gets quite hot may cause some pressure drop in a tire if it was the last one you filled (when the pump got hot filling the others before it) as the air cools back off. I notice this when airing up after off-roading. The pump gets hot and I need to add a bit more air to the 3rd and 4th tire to compensate for the added temp of the air going in through the hot pump. Once the air cools back off those 3rd and 4th tires tend to be a little lower than the first two if I fill to the same PSI.

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100% agree - i prefer to check/inflate the tires after sitting for a day or 2. I just checked mine this morning due to temps dropping below 40 overnight.
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Old 10-19-2020, 10:18 PM #6
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rightyouareken made a great point! I balance my tires with a known gauge but never in the sun. In the evening with three to four hours of no sun or driving...or in the morning before sun hits the tires. My TPMS are also within 1 psi of each other.
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Old 10-19-2020, 10:27 PM #7
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So whats this high end tester you speak of?

I've had a Blue POint for years and it works find but I wouldn't call it high end just because it does better than whole psi readings. I didn't even realize high end for a pressure gauge was a thing.
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Old 10-20-2020, 06:13 AM #8
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There are very accurate gauges which can be calibrated. They're usually only used by race teams and engineers due to the price. Sometimes you are lucky and get a cheap digital unit that is dead on.

I have some of those cheap gauges. I compared them to a gauge owned by a tire expert/engineer. One was very accurate so it stays in my tool box as a reference gauge to everything else I use. I even have some stick gauges that compare surprisingly well and are more accurate than some of the cheap digital units.

In truth, for our use, 1 or 2 psi isn't going to be a major problem. Using proper inflation procedure and even pressures puts you ahead of probably more than 99% of the motoring morons...I mean public.
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Old 10-20-2020, 08:25 AM #9
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When I checked and filled my tires, my rig had been sitting for over 24 hr, however it was outside in the hot Florida sun. The tire gauge I used was a Harley Davidson branded dial gauge that reads from 0 to 60psi so where I would normally keep the 4Runner tires at is right at mid gauge where it is most accurate.
My tires were rotated about 2000 miles ago but that shouldnít account for the difference in the readings. I do realize this is not that important that each tire be exactly the same pressure in this rig for optimal handling, but Iím a bit picky when it comes to my cars, bikes, boats, so I was just curious as to the accuracy of the TPMS.
Iím at my N Carolina home now where the temps are much cooler, so I will recheck everything and see if I can get it to balance out.
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Old 10-20-2020, 09:15 PM #10
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I live in Florida and the sun can easily cause a 2-3 psi difference.
Check when everything has been shaded for a few hours and balance the pressure. Then compare your gauge to the tpms.
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Old 10-20-2020, 11:13 PM #11
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Customer states his tire pressure sensors arenít reading set pressure check and advise.
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