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Tire pressure: Which instrument do you believe?

johnbryanpeters

johnbryanpeters

Hero
Sep 27, 2001
36,126
16,591
Making moss sad in New Haven, Vermont
TPMS systems in our recent Hondas, while better than nothing, have been frustrating. The light will light if there's a problem (when it's not a bad sensor) but the system won't tell us which tire has a problem or what the pressure is and how fast it's changing.

I have also wanted TPMS for the R-Pod, being as it has but two tires and is capable of causing quite a fuss if one fails.

I therefore bought an EEZTire aftermarket TPMS. It has valve caps that measure pressure and temperature and a GPS-sized display that reports measurements and sounds an alarm if pressure or temperature exceed preset limits.

What I got into when setting it up is that there is, of course a two PSIG difference between what my faithful digital tire gauge reads and the TPMS sensors read; the sensors report two PSIG less than the gauge.

I remember my brother, who was a Snap-On dealer for years, bitching about lack of gauge accuracy when Chinese gauges started to hit the market.

What do you use as a tire gauge, and do you believe its readings?
 
JohnE

JohnE

filthy rascist
May 13, 2005
13,452
1,980
Front Range, dude...
I trust the stupid auto reading dohickey on my truck, because it annoys me to have to reset the damn thing if the pressure falls. Spent $20 and had the tires filled with nitrogen and it stays constant...
 
Pesqueeb

Pesqueeb

bicycle in airplane hangar
Feb 2, 2007
40,365
16,849
Riding the baggage carousel.
johnbryanpeters said:
Is there such a thing as a calibrated and certified tire pressure gauge?
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Sure are. We buy them by the dozen here. But as @Adventurous says, they will run you a lot more than the auto parts store cheapies.
Adventurous said:
There certainly is. Lots of places will calibrate your pressure gauge provided it is of high enough quality to offer that sort of thing. You may not like the cost, but it is available.

http://www.pcsllctn.com/services/pressure-gauge-calibration/
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Check with your local higher end tool retailer, or teh interwebz. Personally, I only care as much as to make the lights go away in the new car. If you don't want to spend the money, just pick one gauge and stick with it. Chances are it's within a couple % anyway. I'm pretty picky about the motorcycle, for obvious reason, but I usually fill it with n2 and check it with a cal'd gauge here at work. For airplanes proper inflation = serious business, hence the calibrated gauges.
 
junkyard

junkyard

You might feel a little prick.
Sep 1, 2015
2,601
2,303
San Diego
I generally use my thumb to test if its way to low. But this only really works on car radials. Being that pressure can fluctuate with elevation and temperature. I just use the same gauge to make sure i maintain my settings to what works for the vehicle. My gauge is maybe 15 years old and when i need to replace it i will buy one from "summit racing" and i will get a race car one of some kind or another. Or ill buy a old one at a swap meet and compare it with some other gauges to see how good it is.
 
Toshi

Toshi

Harbinger of Doom
Oct 23, 2001
38,378
7,768
JohnE said:
Why do you say that? Tire pressure stays constant, and I dont have to screw with it all the time. Nitrogen displaces the water that got in there and initially caused the fluctuations...I am open to science...
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Not constant:



That said, it's close in reality. :D

At low pressures of about 1 bar (100 kPa - just a bit less than 1 atmosphere), the compression factor is close to 1. Nitrogen approximates to ideal behaviour at ordinary pressures.
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JohnE

JohnE

filthy rascist
May 13, 2005
13,452
1,980
Front Range, dude...
Toshi said:
Not constant:



That said, it's close in reality. :D
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I am open to science, but I dont believe it. Trying to assimilate with the new grate 'murika and all...


But seriously...all I know is that the low tire pressure sensor in our vehicles doesnt go off all the time now...which lessens my PITA quotient (The Frau will not/can not drive when the light is on in her Loser Cruiser...) which makes JohnE a happy camper...
 
Montana rider

Montana rider

Turbo Monkey
Mar 14, 2005
1,761
2,217

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Toshi

Toshi

Harbinger of Doom
Oct 23, 2001
38,378
7,768
StiHacka said:
It is consistent. A friend of mine has an uber-accurate $$$ pressure gauge for his Ducati superbike where each .1lbs matters, I'll crosscheck the accuracy with him eventually.
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Consistency ==> precision. Hitting the same point on the target repeatedly.

Accuracy == how close that point is to the actual bullseye, which is unknown with uncalibrated instruments.
 
johnbryanpeters

johnbryanpeters

Hero
Sep 27, 2001
36,126
16,591
Making moss sad in New Haven, Vermont
JohnE said:
Why do you say that? Tire pressure stays constant, and I dont have to screw with it all the time. Nitrogen displaces the water that got in there and initially caused the fluctuations...I am open to science...
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I'm not sure what you mean by "displaces" when you're inflating a tire. Dry air or dry nitrogen, I imagine, would each suffice.

Air's 78% nitrogen. Difference in leakage rates, e.g. diffusion through sidewalls, is negligible.

I read a couple of long articles on this recently and of course can't put my finger on them at this time. The essence is that nitrogen's a marketing racket. Aha, just found this, which is reasonably unbiased save that I think their leakage assertion is incorrect.
 
jdcamb

jdcamb

Tool Time!
Feb 17, 2002
19,847
8,451
Nowhere Man!
johnbryanpeters said:
I'm not sure what you mean by "displaces" when you're inflating a tire. Dry air or dry nitrogen, I imagine, would each suffice.

Air's 78% nitrogen. Difference in leakage rates, e.g. diffusion through sidewalls, is negligible.

I read a couple of long articles on this recently and of course can't put my finger on them at this time. The essence is that nitrogen's a marketing racket. Aha, just found this, which is reasonably unbiased save that I think their leakage assertion is incorrect.
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How do they separate Nitrogen from air? What do they do with the rest of the air after they separate the Nitrogen from it? Is it still air?
 
Serial Midget

Serial Midget

Al Bundy
Jun 25, 2002
13,053
1,896
Fort of Rio Grande
I never check the pressure in the Subaru and yet I am somehow still alive? I never knew these sensors existed until I bought the city van, they are a total pain in the ass.
 
JohnE

JohnE

filthy rascist
May 13, 2005
13,452
1,980
Front Range, dude...
johnbryanpeters said:
I'm not sure what you mean by "displaces" when you're inflating a tire. Dry air or dry nitrogen, I imagine, would each suffice.

Air's 78% nitrogen. Difference in leakage rates, e.g. diffusion through sidewalls, is negligible.

I read a couple of long articles on this recently and of course can't put my finger on them at this time. The essence is that nitrogen's a marketing racket. Aha, just found this, which is reasonably unbiased save that I think their leakage assertion is incorrect.
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I'm digging it, but its hard to argue with the results. I have had, and the Frau has had, zero problems with tire pressure since we did the fill...

Will update if there is a change.
 
jdcamb

jdcamb

Tool Time!
Feb 17, 2002
19,847
8,451
Nowhere Man!
Westy said:
The waste air is used to make cheese puffs.
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I buy frozen Phylo dough from BJ's and make my cheese puffs with Spinach, Olives, and Feta. All drippy in oil and shit... The spinach and the cheese melted together makes for a delicious cakey mass. Parchment Paper and Iron tray pans are necessary..... No Nitrogen at all.
 
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jdcamb

jdcamb

Tool Time!
Feb 17, 2002
19,847
8,451
Nowhere Man!
Serial Midget said:
With respect, sir, THAT is not a cheese puff.
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They do get puffy and are very cheesy. The feta melts into the bottom layer of the Phlylo. I coat them with butter and fresh Oregano or parsley. Maybe some fresh squeezed Lemon if I have it. Goes well with Sardines....
 
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