Some discrepancies between tire gauges and TPMS - What's the best gauge to use?

[brasskey]

I want to make sure my tire pressures are accurate and wanted to know if there's some recommended gauges I should be using. Currently, I have the following:


Analog Gauges
Analog Gauge - Looks like one in link, but may be different brand
ARB deflator

Digital Gauges
Aully Park Tire Inflator - use this to inflate to desired psi
Slime Sport Gauge


My digital gauges are reading the same as my TPMS. As an example, I have them inflated to the recommended 41 psi per @gaijin The TPMS and both digital gauges read 41 psi. But, if I use my ARB deflator, it reads about 43 psi as does the other analog gauge. When I deflate down to 41 psi on the ARB deflator, the other analog gauge also reads 41 psi. But, the two digital gauges then read 39 psi as does the TPMS. So, a few psi different, but they're off. I want to believe my TPMS readings are correct, but I wouldn't think my ARB deflator and other analog gauge should be off. Weird that those are consistently 2 psi off the digital reading. I know these aren't the best gauges, so should I get a better gauge? Or, should I just trust the TPMS reading and not worry about it?

 

[hankinid]

@brasskey, you can easily drop $500 + on a calibrated pressure gauge but personally I trust the TPMS. Which is not to say I trust it absolutely down to half a psi or less. I prefer digital gauges and mine are within a pound or 2 of the TPMS. An easy test to verify zero would be to get the truck on jack stands with tires off the ground and remove all 5 valve stems...TPMS should show zero, obviously. I'm not sure how to verify TPMS above zero psi, but a true "calibration" needs to show a zero, mid-range, and upper end deviation from the standard.

 

[gaijin]

I want to make sure my tire pressures are accurate and wanted to know if there's some recommended gauges I should be using. Currently, I have the following:


Analog Gauges
Analog Gauge - Looks like one in link, but may be different brand
ARB deflator

Digital Gauges
Aully Park Tire Inflator - use this to inflate to desired psi
Slime Sport Gauge


My digital gauges are reading the same as my TPMS. As an example, I have them inflated to the recommended 41 psi per @gaijin The TPMS and both digital gauges read 41 psi. But, if I use my ARB deflator, it reads about 43 psi as does the other analog gauge. When I deflate down to 41 psi on the ARB deflator, the other analog gauge also reads 41 psi. But, the two digital gauges then read 39 psi as does the TPMS. So, a few psi different, but they're off. I want to believe my TPMS readings are correct, but I wouldn't think my ARB deflator and other analog gauge should be off. Weird that those are consistently 2 psi off the digital reading. I know these aren't the best gauges, so should I get a better gauge? Or, should I just trust the TPMS reading and not worry about it?

There's really no need to over-engineer the problem.

I purchased a good gauge (99.99 PSI DIGITAL AIR PRESSURE GAUGE - Intercomp Racing) which reads to 0.01psi with an accuracy of 0.1% - it's temperature compensated, barometric pressure compensated, and has stood me in great stead for over 6 years.

When compared to the TPMS pressures in my LC, which indicate only full psi, the tire pressures measured by my fancy dancy gauge are always within 1psi of what the TPMS shows.

In your case, it is important to choose one reference pressure indicator. Since you already have TPMS, I would suggest you use that as your reference. When you need to use a gauge, choose one that is consistent with your TPMS. Doing this, you will always be within 1 or 2psi of the absolutely "correct" pressure.

Bottom line: once you establish a consistant reference pressure indicator it is most important to measure and set you tire pressures regularly when they are cold. Changes in ambient temperature will cause your tire pressures to change. If you check and adjust them regularly, you will stay out of trouble.

HTH

 

[Markuson]

The filler I use with my ARB twin compressor and hose is A digital unit from power tank. It has been extremely accurate and very much reflective of what might be TOMS sensors indicate. So… Either my tea TPMS and our tank gauge device are similarly wrong… Or both are right on the money.

 

[chilibit]

My TPMS readouts are very good. I use very precise gauges for track setups on wheels which clearly don't have TPMS sensors but when I cross check the LC's tires they match within one psi. More than good enough. I can feel 1 psi down on some chassis. On the 200 it really is not that critical IMHO. Three clicks on the display button and there are the values. What is not to like?

 

[Dan Higgins]

Interesting. This has been a constant source of frustration for me. I have used a combination of the gauge on my ARB compressor, a digital gauage, and an analog gauge and the TPMS is always 2-3 PSI lower than those gauges. The gauges themselves tend to vary by 1/2 - 1 PSI. So I just assume that if the TPMS shows 39 PSI first thing in the morning then my tires are at the 42 that I set them to using the other gauges.

 

[gaijin]

So I just assume that if the TPMS shows 39 PSI first thing in the morning then my tires are at the 42 that I set them to using the other gauges.

Based on my experience, I would assume the tires are at 39psi ...

 

[UCrazyKid]

Here's another way to look at it. I don't trust my TPMS sensors. I will do a cold fill with my inflator/digital pressure gauge to the recommend 46psi and then immediately check my TPMS and 3 out of 5 will have variance 47, 46, 45 psi. With TPMS you are dealing with 5 separate sensors that could each be off their calibration, vs a single pressure sensor (the inflator) that is showing consistency. I'm my mind, I'd rather have all tires at the same pressure even if it is +/- 0.5 - 1.0 psi of my target pressure.

 

[Dan Higgins]

So I just checked my tires. Cold. Still in the garage. All except the right rear were at 42 PSI using my Rhino analog gauge. (I expected the RR would be a tad low. It was at 41.) Then I immediately drove to Discount Tire (< 1 mile away) and had them put the tires at 42. No additional air was required except on the right rear. They needed to increase the RR by 1 PSI. On the drive to Discount Tire the TPMS read 39 and 38 for the RR. Afterwards they were all at 39.

So I asked the DT person about this. His suggestion was that the TPMS may be calibrated for sea level. I live at 6,000'. He said that DT has this issue with their automatic air inflation system. Maybe?

 

[gaijin]

So I just checked my tires. Cold. Still in the garage. All except the right rear were at 42 PSI using my Rhino analog gauge. (I expected the RR would be a tad low. It was at 41.) Then I immediately drove to Discount Tire (< 1 mile away) and had them put the tires at 42. No additional air was required except on the right rear. They needed to increase the RR by 1 PSI. On the drive to Discount Tire the TPMS read 39 and 38 for the RR. Afterwards they were all at 39.

So I asked the DT person about this. His suggestion was that the TPMS may be calibrated for sea level. I live at 6,000'. He said that DT has this issue with their automatic air inflation system. Maybe?

Until you have a known good tire pressure measuring tool, you will never know. What I do know for sure is the BS about the TPMS being "calibrated for sea level" is just plain wrong. What I also know is that DT is not known for accurate tire pressure settings.

I just set all 5 of my summer tires to 33.00psi after being at 85 DegF ambient for 10 hours (i.e. 'Cold"). My TPMS indicated 32/32/33/32/32 (incidentally, I'm at 4553 Feet AMSL). Since the TPMS only indicates whole psi, and I don't know when it decides to "round up" to the next whole psi, I must interpret each TPMS measurement as +1psi. This is plenty good enough for me to be assured that my TPMS is a fairly good indicator of my tire pressure - certainly accurate enough for me to recognize a problem. The TPMS is not a substitute for a good gauge, but once you understand where it reads in relation to a good gauge, it's good enough.

My ARB analog gauge reads 2-3psi high @ 40psi, FYI.

HTH

 

[LBridges]

… Since the TPMS only indicates whole psi, and I don't know when it decides to "round up" to the next whole psi, I must interpret each TPMS measurement as +1psi. This is plenty good enough for me to be assured that my TPMS is a fairly good indicator of my tire pressure - certainly accurate enough for me to recognize a problem. The TPMS is not a substitute for a good gauge, but once you understand where it reads in relation to a good gauge, it's good enough.

Not sure if it is a later model feature, but the TPMS reading in TechStream for my truck displays pressures down to the 100ths of a PSI. The following is a cut & paste from Techstream.

ID 1 Tire Inflation Pressure 39.65 psi(gauge)
ID 2 Tire Inflation Pressure 38.91 psi(gauge)
ID 3 Tire Inflation Pressure 39.65 psi(gauge)
ID 4 Tire Inflation Pressure 39.16 psi(gauge)
ID 5 Tire Inflation Pressure 38.66 psi(gauge)

TPMS data displayed between tach and speedo showed 40, 39, 40, 39, and 39 PSIs respectively. From this I am inferring that it rounds like I was taught in math class, i.e., equal/over .5 round up, under .5 round down.

BTW, I have OEM wheels/tires (run @ 32PSI) as well as Rock Warriors/KO2 (run @ 40PSI) on another set of dealer installed OEM sensors. Correlation between the dash display and two external gauges exhibit numbers is within 1 PSI difference (probably within my clumsy measurement error range). So I have a good amount of faith in the TPMS (as implemented in my '17 TLC anyway).

 

[Dan Higgins]

How do I get a "known good tire pressure measuring tool"? I have had 2 digital, and analog and the ARB (which I never use as a gauge because it is high.) All of the non-ARB examples are very close (within .5 PSI) and all are 2-3 PSI above the TPMS. So if were voting, the TPMS loses. That's what has me baffled. How do I get a measurement I can trust as a baseline? Simply trusting TPMS isn't good enough for me as I need to use the manual pressure gauge on my trailer tires so I need to know how it reads and what bias it has.

 

[gaijin]

How do I get a "known good tire pressure measuring tool"?

Do as I did, get one of these: 99.99 PSI DIGITAL AIR PRESSURE GAUGE - Intercomp Racing

Accuracy is not a subject to vote on - all 4 of your gauges could be wrong. Honestly, if you don't want to spend the money for a calibrated gauge, my recommendation is to trust your TPMS readings and pick a consistent gauge that you can calibrate to your TPMS - i.e., if the gauge reads 2psi higher than the TPMS, then fill to a reading on the gauge 2psi more than the desired pressure when using the gauge.

HTH

 

[brasskey]

Thanks everyone. I appreciate the help.

 

[BROKEROB1]

Dan Higgins gave you a nice tip... if you don’t want to drop $100 for a gauge, my experience has also been great with the good old fashioned made in the USA Rhino gauge... shows within 1 psi of my M5 tpms and also my LX570 tpms and is built like a tank!

Rhino USA Heavy Duty Tire Pressure Gauge (0-75 PSI) - Certified ANSI B40.1 Accurate, Large 2" Easy Read Glow Dial, Premium Braided Hose, Solid Brass Hardware, Best For Any Car, Truck, Motorcycle, RV https://www.amazon.com/dp/B01J580F2K/ref=cm_sw_r_cp_api_P1FqBbTGV7205

 

[Dan Higgins]

Thanks, Rob, yet I have been using the Rhino Heavy Duty. That's my analog gauge. That's my issue. I don't know what to trust. @gaijin says to use the TPMS. But the TPMS has been 2-3 PSI low for every gauge I have ever tried. 2 different digital ones. The Rhino. And so on. Consistently 2-3 lower on the TPMS. So I have ordered the $300 Intercomp on @gaijin's advice. It will come next week. I'll post pics of the results. When towing I need to know I can count on my tires been inflated correctly. Especially my trailer tires as I don't have TPMS on them.

I will try the Intercomp when it arrives. If it is no different than the Rhino I will return it. (Bought on Amazon.)

 

[Dan Higgins]

Let me ask a different, possibly dumb, yet related question. Do I need to reset the TPMS every time I alter the tire pressure a few PSI? Such as after I air down when off road? Or air back up again when I am finished? The only time I reset the TPMS is after new tires have been installed or my tires have been rotated.

 

[gaijin]

Let me ask a different, possibly dumb, yet related question. Do I need to reset the TPMS every time I alter the tire pressure a few PSI? Such as after I air down when off road? Or air back up again when I am finished? The only time I reset the TPMS is after new tires have been installed or my tires have been rotated.

Resetting the TPMS resets the trigger pressure for the alarm based on the tire pressure at the time of the reset. If you adjust your tires to the Recommended Cold Tire Inflation Pressure, you should reset the TPMS immediately after. If you TEMPORARILY adjust tire pressures above or below the Recommended Cold Tire Inflation Pressure, there is no need to reset the TPMS. However, be aware that the alarm trigger pressure remains the same unless you reset the TPMS.

OK, this is starting to sound a lot more complicated than it really is. Let's say your Recommended Cold Tire Inflation Pressure is 40psi. Adjust all your tires (when COLD of course) to 40psi and reset your TPMS. This sets the trigger pressure to 25% below the tire pressure when the TPMS was reset - in this case, the trigger pressure is 30psi (75% of 40psi). If you temporarily increase or decrease the tire pressures, the TPMS will still alarm at 30psi.

HTH

 

[Dan Higgins]

OK, this is starting to sound a lot more complicated than it really is. Let's say your Recommended Cold Tire Inflation Pressure is 40psi. Adjust all your tires (when COLD of course) to 40psi and reset your TPMS. This sets the trigger pressure to 25% below the tire pressure when the TPMS was reset - in this case, the trigger pressure is 30psi (75% of 40psi). If you temporarily increase or decrease the tire pressures, the TPMS will still alarm at 30psi.

This is what I do so I'm good to go on that. Now it is just a matter of seeing what results I get from the Intercomp gauge compared to the Rhino and the TPMS. If the Intercomp and TPMS match and the Rhino is off then I'll toss the Rhino. If the Rhino and Intercomp match and the TPMS is off then I'll toss the TPMS. Actually, if the Rhino and Intercomp match I'll return the Intercomp and to from there.

 

[brasskey]

This is what I do so I'm good to go on that. Now it is just a matter of seeing what results I get from the Intercomp gauge compared to the Rhino and the TPMS. If the Intercomp and TPMS match and the Rhino is off then I'll toss the Rhino. If the Rhino and Intercomp match and the TPMS is off then I'll toss the TPMS. Actually, if the Rhino and Intercomp match I'll return the Intercomp and to from there.

Interested to see those results. Let us know how it goes.