TPMS and tire gauges

[MerlintheMad]

Hi all, I just got back from Jerry Seiner for an oil change/maintenance. The TPMS "discrepancy" has been bugging since I got my Nitto Motivo A/S tires two weeks ago this Friday. So I asked the tech to look into it. "The TPMS reading on the LCD seems to be about four to five pounds low." Also, "I had Big O inflate my tires to 40 in the front and 38 in the rear. Interestingly, as I was pulling out, the TPMS showed the 'four pounds low' readout at first, then abruptly shifted to 39 front and 37 rear. One pound off, that's acceptable. But next morning, it was back to four pounds low showing on the LCD." The Big O guy told me to get the dealer to adjust to the computer. So, this morning, that is what I said I wanted.

The Kia tech said, "Your TPMS is doing what it's supposed to be doing. Our pressure gauge shows a one to two pound difference at the tire, with what the TPMS is sending to the instruments."

Hmm. It isn't that cold around here. The tires should not have lost c. four pounds from cooling since Big O inflated them to 40 in front and 38 in rear. When I pulled into Big O, the readout showed 36 in front. So inflating to 40 psi, then having the TPMS send back 39, then ever since that singular moment the TPMS shows anywhere from 34 to 38 psi (after driving for a while), and nowhere near 40: do I assume that someone's equipment is off by more than one or two pounds? Or do I just stop thinking about it unless the TPMS starts to show a drastic loss of pressure in one tire? Is that all the TPMS is really good for? Because I sure haven't seen any consistency between my handheld tire gauge(s), Big O, Jerry Seiner and the LCD psi display.

 

[Waynerm002]

My advice check it every 2 week to a month, if the temps change drastically and is going to stay there, set for that temp and you will be fine. Before this auto stuff, I checked mine manually and continue to do so. I use the in car system as a gauge to tell me if one is way out of whack, meaning a slow leak or a fix will be needed. I normally can tell based on how the car feels and handles if it's too low. Yeah, sometimes I get busy and don't check as open and go by feel.

 

[MerlintheMad]

Well, just checking again, the discrepancy (in spite of what the Jerry Seiner techie told me) remains four pounds. At the tire, the pressure gauge says "40". The LCD said 36 all around.

 

[SteveCo]

I'd suspect your tire pressure gauge. Your dealer likely has a more reliable/commercial gauge - have them verify the tire pressure against the TPMS readout again, and take your gauge along and see what it reads vs. theirs. Don't know how long your tires had to cool down after driving to the dealer, but 4 or 5 lbs. higher pressure than when cold is normal for a warm (driven) tire.

Also consider that your TPMS system is showing the output from four different pressure transducers. If the readings are a consistent offset from what you are reading from your gauge, chances are they aren't all defective.

 

[MerlintheMad]

My tire gauge is brand new, just bought it from O'Reilly's last week. Only c. six bucks, though. Nice two-way metal head. Feels very solid. But if it were off by one or two pounds to the high side. And the TPMS were off by one or two pounds to the low side, well there you go.

 

[Mr Skillet]

Tire pressures can very by 3-4 lbs between a cool morning and fully warmed up after a cruise on the hwy. If you have a good accurate digital guage( there are very accurate analog ones too but they are pricey), You should rely on that as an accurate judge, most in tire tpms sensor will vary by 1-2psi from a stand alone gauge.

I typically adjust pressure after the tires have cooled completely in the evenings as temps here are in the mid 60's-low 70's after dinner. I inflate to 36 psi based on door sticker. During the middle of the day if I'm doing freeway driving, temps will climb to about 39/40 psi with ambient temps in the low 80's

 

[MerlintheMad]

This remains very consistently c. four pounds low on the LCD readout.

( there are very accurate analog ones too but they are pricey)

Where do you buy "pricey" accurate old school tire gauges?

I had a digital gauge from Radio Shack for well over ten years. But the battery finally died. When I took the handle halves apart, the battery was buried inside more hardware and miniature screws. I bagged it as too much trouble (you'd have to be looking at it to appreciate my decision). There were no digital offerings at O'Reilly's, which surprised me in this digital world: I expected an array of digital and maybe one analog offering.

 

[Mr Skillet]

Accutire MS-4021B Digital Tire Pressure Gauge https://www.amazon.com/dp/B00080QHMM/ref=cm_sw_r_cp_apa_K42WBbVXN6YBM

That's what I use. There are racing analog ones, but 10x the price and not needed unless you're at the track and need an inline guage. Are you getting 4psi lower between.your gauge and Tpms when tires are warm and cold?

 

[MerlintheMad]

Are you getting 4psi lower between.your gauge and Tpms when tires are warm and cold?

Only 2 lbs difference cold. I checked the pressure in the LF and RR tires. This morning it was cold and the pressure was 36 at the tire. When the LCD started to register it showed 34 psi all around. After sitting for over three hours, in the middle of the afternoon it was still chilly and the RF and LR tires showed 36 psi. The LCD showed 34 psi again. So very consistently 2 lbs off cold. The handheld gauge is probably the inaccurate tool. But if both were off in opposite directions by only a pound, that would produce the difference this morning. I'd need a second handheld gauge to "triangulate" readings and make a more accurate determination.

 

[CDv6]

Accutire MS-4021B Digital Tire Pressure Gauge
That's what I use.

I had a Craftsman digital gauge for a long time. It had a bleeder valve so the gauge didn't need to be re-seated when making fine adjustments after topping-off the pressure. I broke the LCD screen, and haven't bothered to order a new one yet. Perhaps I should do that now, since Sears just filed for bankruptcy...

 

[ZyroXZ2]

I learned from experience that going super cheap on a tire gauge can backfire. For the longest time, Big O was overinflating my tires... right up until I realized it was my gauge, lmao

Fortunately, I had never bugged them about it since the less other people touch my stuff, the better... so I saved myself from looking/sounding like a moron. Instead, it crossed over into Winter, so I went to put air in the tires on a compressor that had its own gauge... only to find that the gauge on the compressor read different than my tire gauge. Needless to say, I ended up buying an analog gauge for $30. It's been spot-on since, lol

 

[MerlintheMad]

https://www.amazon.com/dp/B074TD89X...3b320cf86cd1#HLCXComparisonWidget_feature_div
When I commit to change, I commit all the way. I'm looking at this one. I have a compressor, which I bought a couple of months ago.

 

[Nac]

You may want to read the specifications for that gauge again; it states "The Vondior...calibrated highly accurate to ±1% full scale of 200 PSI range with display resolution of 0.5 PSI"

1% of 200 psi is 2 psi which means even though it reads out in .5 psi increments it can be off by as much as 2 pounds anywhere between 0 and 200 psi. Personally I prefer a more accurate gauge.

This one is similar in price reads 0-60 PSI in .2 psi increments and has .8% accuracy meaning its accurate to 0.48 psi (about a half a pound). www dot longacreracing dot com/products.aspx?itemid=1715&prodid=7356&pagetitle=Basic-Digital-Tire-Pressure-Gauge

there are plenty of others out there in that price range that are way more accurate and keeping the full scale range lower gives a more accurate reading. I don't own anything that runs tires at over 50 psi.

 

[MerlintheMad]

You may want to read the specifications for that gauge again; it states "The Vondior...calibrated highly accurate to ±1% full scale of 200 PSI range with display resolution of 0.5 PSI"

1% of 200 psi is 2 psi which means even though it reads out in .5 psi increments it can be off by as much as 2 pounds anywhere between 0 and 200 psi. Personally I prefer a more accurate gauge.

This one is similar in price reads 0-60 PSI in .2 psi increments and has .8% accuracy meaning its accurate to 0.48 psi (about a half a pound). www dot longacreracing dot com/products.aspx?itemid=1715&prodid=7356&pagetitle=Basic-Digital-Tire-Pressure-Gauge

there are plenty of others out there in that price range that are way more accurate and keeping the full scale range lower gives a more accurate reading. I don't own anything that runs tires at over 50 psi.

Thanks! And that was a helpful way to circumvent the "New/Newish Member" delay on posting links. Thanks for providing!

So, that gauge just screws into the end of a compressor hose?

 

[SteveCo]

Thanks! And that was a helpful way to circumvent the "New/Newish Member" delay on posting links. Thanks for providing!

So, that gauge just screws into the end of a compressor hose?

It's only a pressure gauge, not a combination gauge/filler. It's just used to check pressures.

 

[MerlintheMad]

It's only a pressure gauge, not a combination gauge/filler. It's just used to check pressures.

Dang. Bummer. I want a gauge that good on the end of my hose, so that I can watch the psi as I inflate.

 

[Ozstung]

Dang. Bummer. I want a gauge that good on the end of my hose, so that I can watch the psi as I inflate.

Sounds naughty.....sorreeeeee

 

[Nac]

Dang. Bummer. I want a gauge that good on the end of my hose, so that I can watch the psi as I inflate.

Here you go, its a bit pricey @ $163.00.... digital gauge 0-60 psi reads to 0.1 psi and is accurate to 0.3% (0.2 psi) comes with its own protective case. I could see getting extremely upset if I dropped something like this.

www . longacreracing . com/products.aspx?itemid=1715&prodid=7348&pagetitle=Digital-Quick-Fill-Tire-Pressure-Gauge-0-60-psi

 

[MerlintheMad]

Here you go, its a bit pricey @ $163.00.... digital gauge 0-60 psi reads to 0.1 psi and is accurate to 0.3% (0.2 psi) comes with its own protective case. I could see getting extremely upset if I dropped something like this.

www . longacreracing . com/products.aspx?itemid=1715&prodid=7348&pagetitle=Digital-Quick-Fill-Tire-Pressure-Gauge-0-60-psi

Thanks again. Looks tempting. I really, really, really, want to be able to fill and watch the psi at the same time. And I really, really, really, want accuracy at the tire; that way I can KNOW if the LCD psi readout is accurate, or not.

(edit: no "add to cart" so no way to buy; hmm ...)

 

[Nac]

Longacre products are generally sold at speed/racing shops; you can get them online at Summit Racing, TH Motorsports or from Longacre through Amazon. The one that connects to your compressor hose, Longacre Part #: 52-53008, is about $146.00 at Amazon (the best price I could find in the 2 minute search i did).

I have a Longacre "Semi Pro Digital Tire Pressure Gauge" its 0-60 psi in 0.1 psi increments and 0.5% accuracy (0.3 psi). It does not connect to my compressor hose which works for me because its a bit more portable.

Using my gauge I have found the TPMS system on the stinger does not update quickly enough to get good comparable readings. If I take a cold tire pressure measurements using the gauge in the morning (car in garage all night) it compares with TPMS as soon as TPMS goes active (I start driving).

If I take pressures with the gauge on hot tires (driving a little while) the TPMS sometimes matches sometimes it does not, however if I leave the TPMS display up it eventually matches closely to the gauge readings within a few minutes.

I don't know what the TPMS update time cycle is, but it appears to be in minutes so readings from a gauge will not always compare to the TPMS depending on how recently the TPMS retrieved data from the tire sensors.

I believe the TPMS its pretty accurate (at the instant in time that it updates), since its not a high priority system the computer looks at it relatively infrequently compared to high priority signals that the computer is processing a few hundred times a second.

The TPMS is there to let you know about a slow or small leak in your tires, based on that priority, if it take a minute or two to accomplish its job that's ok