Tire Gauge Calibration?

676 Views 14 Replies 7 Participants Last post by m4ca, 2 mo ago

Marek K

Discussion Starter · 4 mo ago

2

This isn't specific to the Renegade... Except that I'm trying to keep accurate tire pressure on my 2021 Trailhawk.

I've got several decent-quality (I think) dial-type tire gauges -- one in each of our vehicles, and a couple on the garage shelf.

Most gauges agree pretty-well with one another, to with one psi or so.

Two of the gauges are like this:

Measuring instrument Tool Gas Circle Gauge

And they don't agree with one another. One reads about three psi higher than the other, on the identical tire. And, again, that's higher than the other tire gauges I've got.

I notice there's a knurled collar on the chuck (I think it's called). It screws off, and the core (again I think) is slotted:

Measuring instrument Gas Metal Cylinder Auto part

Is there any way to "calibrate" the tire gauge using any of those bits?

By the way, the TPMS system on the Traihawk tends to show a few psi higher than most of my gauges, even before the tires heat up with driving. So I'm trying to figure out if the TPMS system is inaccurate, or most of my tire gauges...

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Marek K

Discussion Starter · #2 · 4 mo ago

Here's what I mean...

I checked tire pressure this morning at ambient temperature, and two different tire gauges were showing my Trailhawk has 36 psi all around (which is the recommended tire pressure).

I drove the Trailhawk a few hundred meters down the street -- just enough to "wake up" all the sensors, but not enough to heat up the tires. The display showed 38 psi all around:

Speedometer Steering part Vehicle Motor vehicle Tachometer

So which is correct? If I know, I can compensate.

Or is a measured difference of 2 psi not enough to make a difference?

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Ops

· #3 · 3 mo ago

tires will fluctuate due to temperature. so hard to gauge , back and forth in real time

Marek K

Discussion Starter · #4 · 3 mo ago

Ops said:
tires will fluctuate due to temperature.

Yeah, I know that. But again, I measured the pressure with the tire gauge, then immediately drove the Trailhawk a few hundred meters at about 20 MPH just to wake up the sensors. Certainly not long enough to heat up the tires. Difference of 2 psi, gauge vs. the TPMS system.

jeff1

· #5 · 3 mo ago

Marek K said:
This isn't specific to the Renegade... Except that I'm trying to keep accurate tire pressure on my 2021 Trailhawk.

I've got several decent-quality (I think) dial-type tire gauges -- one in each of our vehicles, and a couple on the garage shelf.

Most gauges agree pretty-well with one another, to with one psi or so.

Two of the gauges are like this:
View attachment 2396355895

And they don't agree with one another. One reads about three psi higher than the other, on the identical tire. And, again, that's higher than the other tire gauges I've got.

I notice there's a knurled collar on the chuck (I think it's called). It screws off, and the core (again I think) is slotted:

View attachment 2396355897

Is there any way to "calibrate" the tire gauge using any of those bits?

By the way, the TPMS system on the Traihawk tends to show a few psi higher than most of my gauges, even before the tires heat up with driving. So I'm trying to figure out if the TPMS system is inaccurate, or most of my tire gauges...

must spend at least $40.00+ for an accurate gauge. then they can still be +/- 3psi off

Marek K

Discussion Starter · #6 · 3 mo ago

jeff1 said:
must spend at least $40.00+ for an accurate gauge. then they can still be +/- 3psi off

"Accurate" and "+/- 3psi" seems like an oxymoron.

Everything I've got -- all my gauges and the Trailhawk's TPMS system -- seem to be within 3 psi. So I can't get any better than that...?

Nev

· #7 · 3 mo ago

The TPMS sensor are not accurate enough to be used as a gauge. I set with pump gauge, in bar, and drop the pressure down to what I want.
Then the TPMS, set to bar, gives even readings on all 4 tyres.

e.g. inflate to 2.6 with pump, drop to 2.5 with guage, reads 2.5 on TPMS.

rsanges

· #8 · 3 mo ago

Being a Fiat at heart. I assume the default pressure units are kPa (kilopascals). And I also assume the minimum resolution is 10 kPa which is about 1.5 psi. So if it rounds to the nearest 10 kPa then, after it does the conversion to psi, every few psi change will skip a least significant digit.

For example, 230 kPa = 33.36 psi which rounds to 33 psi. 240 kPa = 34.81 psi which rounds to 35 psi. No 10 kPa increment will round to 34 psi.
250 kPa = 36.26 psi (36 psi), 260 kPa = 37.71 psi (38 psi)

Edit: the default units may also be tenths of a bar which is the same as 10 kPa. Ah, the joy of metric units. If only my life was so simple.

Marek K

Discussion Starter · #9 · 3 mo ago

Nev said:
The TPMS sensor are not accurate enough to be used as a gauge. I set with pump gauge

Pump gauge? What's that -- the gauge that's integrated with your pump?

Nev said:
2.5 with guage, reads 2.5 on TPMS.

So in your case, your gauge reads the same as the TPMS?

rsanges said:
I assume the default pressure units are kPa (kilopascals). And I also assume the minimum resolution is 10 kPa which is about 1.5 psi.

Yeah, metric tire pressure measurements are always in tenths of a Bar -- which is indeed about 1.5 psi (actually 1.45037738 psi

).

So it's just barely possible that the TMPS showing 2 psi higher than the gauge (38 vs. 36 psi) could because of metric rounding...

OK, at least for now I'll set pressure to the recommended 36 psi using my tire gauge, and assume that's correct. And assume that the TPMS-displayed pressure will show about 2 psi higher than that.

darthcuda01

· #10 · 3 mo ago

I bought a Milwuakee 18v inflator which has a set it and forget it design. I checked it with a gauge before and after, also checked against the renegade readings and it was within 1 psi (which was probably lost in screwing/unscrewing coupling). So of you want something hassle free and accurate it's worth a look. It's not an inexpensive option though.

Marek K

Discussion Starter · #11 · 3 mo ago

darthcuda01 said:
I bought a Milwuakee 18v inflator which has a set it and forget it design. I checked it with a gauge before and after, also checked against the renegade readings and it was within 1 psi (which was probably lost in screwing/unscrewing coupling).

I've got a Kobalt inflator like this for the garage:

Sleeve Gesture Liquid Gas Electric blue

Not real cheap; now about $75.

While it pumps well and is convenient, I've found that the pressure gauge in it varies wildly as it gets older -- up to 5 plis or more, and never consistent. So I use it for inflation, but always check with a hand-held gauge.

So your TPMS pressure matches your gauge to within 1 psi or so? What size tire do you have, and what's the recommended inflation? The bigger the tires, the higher the recommended inflation in general. And if rsrange's theory about metric rounding is correct, and if your inflation is less than my 36 psi, that might make sense...

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darthcuda01

· #12 · 3 mo ago

I have stock tire size, for 2018 sport. 215/65 R16 recommended is 35 psi.

Marek K

Discussion Starter · #13 · 3 mo ago

darthcuda01 said:
I have stock tire size, for 2018 sport. 215/65 R16 recommended is 35 psi.

OK. So maybe mine being 36 psi is just enough for the "metric rounding" to make a 2-psi difference...

Marek K

Discussion Starter · #14 · 3 mo ago

rsanges said:
Being a Fiat at heart. I assume the default pressure units are kPa (kilopascals).

You know, you may be on to something with your crazy "metric-rounding" theory.

I took the Trailhawk out this morning. After all the TPMS sensors woke up, three were showing 38 psi, and one was only 36 psi. After driving a bit farther the 36 psi one suddenly jumped up to 38 psi (bypassing 37). So it may have been just a hair lower than the others, just enough to be on the other side of the threshold.

And note that it jumped by 2 psi.

A bit farther, and one of the other tires warmed up enough to rise to 39 psi. So it incremented by 1 psi at that point.

I'm not sure what all this means to my original question, but metric rounding does seem to be "a thing"...

Hmmm... My Trailhawk's Uconnect system allows me to set just the tire pressures to show in Bar, while other stuff (distance, speed) stay Imperial. I just may have to do that.

Annnnd... I just noticed the tire pressure sticker recommends 35 psi, instead of the 36 that I'd though was recommended.

Rectangle Font Parallel Ticket Electric blue

So maybe I need to reduce cold pressure to 35 psi, instead of 36 psi. And set the units to Bar (which would be 2.4 Bar). That way maybe the TPMS reading will match the gauge pressure...

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m4ca

· #15 · 2 mo ago

rsanges said:
Being a Fiat at heart. I assume the default pressure units are kPa (kilopascals). And I also assume the minimum resolution is 10 kPa which is about 1.5 psi. So if it rounds to the nearest 10 kPa then, after it does the conversion to psi, every few psi change will skip a least significant digit.

For example, 230 kPa = 33.36 psi which rounds to 33 psi. 240 kPa = 34.81 psi which rounds to 35 psi. No 10 kPa increment will round to 34 psi.
250 kPa = 36.26 psi (36 psi), 260 kPa = 37.71 psi (38 psi)

Edit: the default units may also be tenths of a bar which is the same as 10 kPa. Ah, the joy of metric units. If only my life was so simple.

This is an old thread but with the fluctuating spring weather I have been able to confirm that I only see readings of 33, 35, 36, and 38 psi. Never 34 or 36! Looks like your assumptions of metric measurement being converted to our wacky units is spot on.

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