TPST accuracy?
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Laughing Gas
Joined: Jul 2017
Posts: 960
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TPST accuracy?
So I got one of those Jaco air gauges that was highly recommended from members here—the kind you could bleed to reduce to a specific psi. But it never matches the supposed psi the truck says it is. Do I need to send my jaco back to Amazon or is the truck psi off?
Jaco said front tires were 60, truck says it was 63.
Jaco said rear tires were 75, truck says 78.
Do I assume truck is correct?
Jaco said front tires were 60, truck says it was 63.
Jaco said rear tires were 75, truck says 78.
Do I assume truck is correct?
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Laughing Gas
Joined: Jul 2017
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Hotshot
Joined: Oct 2015
Posts: 19,711
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From: Wyoming
I fill the tires with the goal of making the PSI reading on the truck right. My assumption is that the TPMS cost more than the gauge so they could be more accurate. Getting the truck to display the exact, expected PSI is easier than remembering to add/subtract by X amount.
I have yet to find a gauge that agrees exactly with the vehicle's TPMS.
I have yet to find a gauge that agrees exactly with the vehicle's TPMS.
Cargo Master
Joined: Dec 2003
Posts: 2,182
Likes: 7
From: Saint Augustine, FL
This is a calibration issue and is typical of tire pressure gauges. For accuracy and repeatability, digital is typically better. Mechanical gauges are prone to all kinds of calibration issues. Dropping a dial mechanical gauge typically knocks it out of calibration.
Without a known standard for reference it is impossible to know which is more accurate, the hand-held gauge or the TPMS system. As an example, I set the tire pressures on my truck with a highly accurate gauge and then immediately checked the TPMS readout and found them all off slightly and none by the same amount.
Also note that parking the truck with the sun shining on the tires on only one side, on a cold day, will result in significant difference in pressures from one side to the other. This will usually equalize within a few minutes of driving. The inverse is also true: if you set your tire pressures, on a cold day, with the sun shining on the tires on one side, they will then be off once you start driving and the pressures equalize.
I set my pressures using my good gauge and then simply monitor the TPMS readouts from time to time to be sure I don't have a tire going down, or that I need to adjust due to seasonal changes in temperature.
Without a known standard for reference it is impossible to know which is more accurate, the hand-held gauge or the TPMS system. As an example, I set the tire pressures on my truck with a highly accurate gauge and then immediately checked the TPMS readout and found them all off slightly and none by the same amount.
Also note that parking the truck with the sun shining on the tires on only one side, on a cold day, will result in significant difference in pressures from one side to the other. This will usually equalize within a few minutes of driving. The inverse is also true: if you set your tire pressures, on a cold day, with the sun shining on the tires on one side, they will then be off once you start driving and the pressures equalize.
I set my pressures using my good gauge and then simply monitor the TPMS readouts from time to time to be sure I don't have a tire going down, or that I need to adjust due to seasonal changes in temperature.
Hotshot
Joined: Oct 2015
Posts: 19,711
Likes: 12,852
From: Wyoming
My experience that I used in my prior post was with digital gauges. As Steve said, there are a lot of variables in the mix. I figure 2 PSI to be within the margin of error and I don't worry about it. 5 PSI difference and I start to worry.
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Mountain Pass
Joined: Feb 2018
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From: Reno-Tahoe region
My experience is that a TPMS may not match exactly a good air gauge. Mine were very different, so I checked the air pressure with several different gauges I had accumulated over time. Turns out the 1 gauge I was trusting was way off. The other 4 were very close to what I expected the air pressure to be, and closer to the TPMS.
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Junior User
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I did a lot of tire gauge research several years ago and the biggest thing I found was that you wanted a gauge that had your specific target PSI in the middle of the gauge range. Meaning if you want 70 psi in your tires use a gauge that has a max reading as close to 140psi as possible for maximum accuracy in the 70psi range. Beyond that the gauges with Dials were generally considered pretty accurate but they are more delicate than the stick types.
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Laughing Gas
Joined: Jul 2017
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Cargo Master
Joined: Dec 2003
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From: Saint Augustine, FL
More Turbo
Joined: Mar 2005
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My two hand held gauges will say one psi, and my front two tires and rear two tires will all be different in the TPMS.
Odd, all four tires monitors are off a bit, some low, some high. I set them with one gauge, and leave them that way. Wish the TPMS was a bit more accurate.
Odd, all four tires monitors are off a bit, some low, some high. I set them with one gauge, and leave them that way. Wish the TPMS was a bit more accurate.
Senior User
Joined: Sep 2017
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I broke down and got a Power Tank TIG 8340 digital gauge/inflator. Not cheap...but a really nice gauge/inflator that makes setting pressure easy and safe (long hose and lock-on chuck).
More Turbo
Joined: Nov 2005
Posts: 698
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From: Rural Northern California
Typically I use the TPMS system as an alert system only to let me know if any tire has dropped significantly.
Spinning around at high speeds and temps along with impacts can't be too kind to those TPMS sensors.
It's habitual for me to go around all 4 (or 8) corners with a quality hand held gauge before each significant trip to verify my pressures.
This is probably an inappropriate behavior I have brought over to the truck from dirt biking.
In dirt bike riding a 2 psi pressure change makes a huge difference in the way the bike handles as we run those tires at 6 to 8 psi.
Spinning around at high speeds and temps along with impacts can't be too kind to those TPMS sensors.
It's habitual for me to go around all 4 (or 8) corners with a quality hand held gauge before each significant trip to verify my pressures.
This is probably an inappropriate behavior I have brought over to the truck from dirt biking.
In dirt bike riding a 2 psi pressure change makes a huge difference in the way the bike handles as we run those tires at 6 to 8 psi.