Tire pressure on board reading accurate?

[dragoneggs]

When I picked up my new JLR my tires were all set at 40psi per the on board computer. I dropped them all 5psi to 35psi and figured that was a good on road running pressure for starters.

After installing the ARB dual compressor, I decided to check the pressure manually with a dial meter and it read 30psi. Checked them again with a second dial meter and inflater and it also was 5psi lower than the Jeep is measuring.

Anyone else seeing a big discrepancy like this? Is there possibly a calibration that needs to be done?

Edited: Fixed my math.

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[engineXI]

Tested mine several times. Always spot on

 

[Yellow Cake Kid]

I use an inexpensive digital meter to set my tires where I want them. I imagine it to be wholly inaccurate but it is impressively precise in terms of consistent repeatability so it makes it easy for me to set the tires for the feel I want.

That said the external gauge seems to measure as much as 3 psi lower than my TPMS, depending on weather conditions. I also have an impressively expensive name brand calibrated once but not certified 4" dial gauge, and it also reads as much as 3 psi lower than my TPMS.

Keep in mind that an external gauge reads a relative pressure, relative to the external ambient air pressure, and is referenced to what ever ambient pressure it was calibrated with, while the TPMS sensors measure an absolute pressure, they don't have any reference to the air outside.

I have to admit, I have been trying to wrap my head around the implications of the differing function and have yet to comprehend what one should expect when comparing the results of the two systems. Every time I think I have it figured out I figure out I am fooling myself.

In theory, a good calibration on a absolute system could be very accurate. Regardless, in my experience the TPMS are remarkably precise, as the relationship between what I measure with my digital meter and observe with the TPMS read seems to be remarkably consistent.

In other words, I found a way to relate a consistent reading with the comfort and handling I desire. That works for me despite the fact that I really do not know what the actual tire pressure is.

Good luck.

 

[jaymz]

When I picked up my new JLR my tires were all set at 40psi per the on board computer. I dropped them all 5psi to 36psi and figured that was a good on road running pressure for starters.

After installing the ARB dual compressor, I decided to check the pressure manually with a dial meter and it read 30psi. Checked them again with a second dial meter and inflater and it also was 6psi lower than the Jeep is measuring.

Anyone else seeing a big discrepancy like this? Is there possibly a calibration that needs to be done?

They are more accurate than your math.

But seriously, they are pretty accurate, and there’s no calibration to be done. You probably don’t have the best quality dial gauges.

 

[Chocolate Thunder]

They should be accurate to within 1 psi.

 

[Lightguy]

“A man with 1 tire gauge always knows his tire pressure, a man with 2 gauges is never sure”

 

[Vinman]

My 2021 is reading about 2 psi high when compared to my tire gauge.
I have 4 or 5 tire gauges that are all within about a half a psi of each other so I’m fairly confident the Jeep is reading a bit high.

 

[AZJeepGuy]

I picked up my JLUR a couple weeks ago and the tires were at 39 psi. That quickly went to 43 once I got on the freeway. I stopped at Walmart and bought a gauge and dropped it 5 psi. The gauge and the computer have matched every time I've checked. Now I'm at 33 cold which turn to 37 once warm. Rides much better.

 

[MrMischief]

I have some cheap analog dial tire gauge that I use when airing up (airing down my deflators are set to 15 psi and I just trust they are accurate). The dash gauge matches my tire gauge. I don't know how accurate either is, but I figure good enough. If they didn't match each other I'd go off of the dash gauge. Not because I necessarily believe it is more accurate, but because that's the one that'll set off the annoying light if it gets too low.

 

[Reinen]

I've seen my dash PSI change from 34 PSI to 29 PSI and back up to 33 PSI within a 1/10th of a mile on 3 of 4 tires. OEM TMPS sensors (Pre-6/21 change). So I'm thinking they're not quite spot on.

 

[dragoneggs]

They are more accurate than your math.

But seriously, they are pretty accurate, and there’s no calibration to be done. You probably don’t have the best quality dial gauges.

Ha ha... fixed it. I cracked myself up rereading it.

 

[dragoneggs]

Based on a few comments here, I am thinking my on board TPMS is way off. Gonna take it in to the dealer. Also noticed a couple of drops of tranny oil on the case and on the ground. WTH!

 

[Yellow Cake Kid]

I live at elevation and my external gauges were manufactured near sea level. Our Jeep isn't a daily transportation driver but we drive in the desert several times a week. Every time I drive our Jeep, I air down and match all 4 tires to within a 1/10 of a psi. My favorite, and constant dash display is the TPMS info. I think this is because I am fascinated by watching how sunlight and shadow so quickly influence the pressure readings, and I like to know if I can depend on my tires to have maintained pressure when I get in a off camber situation because many times it is of grave concern that everything operate as expected.

When we start to head home, I air up the tires. Sometimes I just get them close out on the trail and then match them back up to the 1/10th psi the next morning in my garage when they are cool and the temperatures are equalized. Sometimes I find a cliff shadow or line the Jeep up with the sunlight and match them before heading home.

I am, for all intents and purposes a tire pressure nerd, and have never seen the Jeep's TPMS match the gauges I use.

I am surprised that so many here can confidently state that they observe everything matching. I guess a lot of people live at lower elevations.

I don't think there is any easy access calibration procedure available for the TPMS system.

Here's some basic info about measuring tire pressure:

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=167

 

[BullMoose1776]

This thread needs a calibration...

 

[dragoneggs]

This thread needs a calibration...

Maybe so but I'm 5psi off so any suggestions?

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