tire pressure

Assuming all things being equal, if it's 34 degrees and all four tires read

25 psi what approx. was the tire pressure when the temperature was 68 degrees? Is there a simple way to judge the accuracy of one's tire gauge? I've asked my town's weights and measures person when I happened to see him checking the fuel pumps at a gas station and he said he didn't have any way to check pressure gauges. The one I carry with me in my trunk has a flexible braided hose and a brass gauge with a bleeder.

mark_

Reply to
mark digital©
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Well, when Mark gets serious, he REALLY gets serious!!

Seems to me I recall something about 4 PSI, but then, I saw little green Martians, too...

I think BGM posted something about this in the spring last year, and there are tables on the Interenet to help calculate this, if not an actual calculator somewhere.

As Tegger used to say "google is your friend!"

Reply to
Hachiroku

25 psi is way too low no matter what the ambient temperature is. There is no simple way to judge the accuracy of one's gauge, but the outlet pressure gauge on my compressor matches the gauge on my Wilton tire inflator, which matches the gauge on my pencil-type tire pressure gauge. That being the case, I just use the gauge on my tire inflator.

For street use, 1 or 2 psi does not make a huge difference. The trick is to make sure that all 4 tires are inflated evenly, or if the vehicle manufacturer calls for higher pressure for the rear tires, that the difference between the front and the rears are correct. For most passenger cars, I recommend 3 or 4 psi higher than factory recommended for longer tire life and fuel economy.

Reply to
Ray O

I can't think of any practical way to check the accuracy of your gauge, but I can answer your first question.

At typical tire pressures and outdoor temperatures we can assume that air will behave as an ideal gas. As such at constant volume, P2/P1 =3D T2/T1, where T is the absolute temperature measured in Rankine (F+460).

In your case, (P2)/(25 psi) =3D (68+460)/(34+460) =3D> P2 =3D 26.7 psi

Reply to
bcattwood

I can't think of any practical way to check the accuracy of your gauge, but I can answer your first question.

At typical tire pressures and outdoor temperatures we can assume that air will behave as an ideal gas. As such at constant volume, P2/P1 = T2/T1, where T is the absolute temperature measured in Rankine (F+460).

In your case, (P2)/(25 psi) = (68+460)/(34+460) => P2 = 26.7 psi

Yeah! What he said! ;)

Reply to
Hachiroku

The following web site claims that good tire dealers have a "master gauge," whatever that is, and can check your tire gauge....

I'll ask next time I'm in my local shop, which is usually once every couple of months...

Reply to
timbirr

OPPS, forgot the URL:

formatting link

Reply to
timbirr

Really? I'm much more relaxed now than ever.

What happened to a retired truck driver who went by the name Philip? and was a regular in this group? Did he change his name or just doesn't frequent this group?

Reply to
mark digital

I get occasional e-mails from him but I don't know whether he is lurking or not frequenting this group.

Reply to
Ray O

And if you want to get totally paranoid about how accurate your pencil gauge is, you can make a calibrator for yourself and you can use it anytime the mood strikes you.

You can order a +/- 1% pressure gauge with a NIST traceable calibration certificate for under $40 (McMaster-Carr 3543K21 2-1/2" dial bottom connection)

After that, all you need is a 1/4" pipe tee, a male Schrader to male pipe thread adapter, and a male disconnect plug that fits your shop air piping system (or the output of a portable compressor) after the regulator, a reducing bushing or two (the Schrader's are usually 1/8" NPT and the gauges and air plug 1/4" NPT) and a little Teflon tape to put it all together with.

You set the compressed air source regulator to 10, 20, 30, 50 pounds on the calibrated gauge, plug the pencil gauge under test onto the Schrader, and compare the two readings. Bada-Bing.

You can make little labels for the pencil gauges saying "Reads 5 PSI High" if you can't remember.

And every 5 or 10 years you pack your calibration set securely in a box and send the whole thing off to a Metrology Lab with a ($20) bill, and they check it for accuracy (adjust as needed) and give you another (X)-year calibration certificate.

(If you make friends at the lab, just put a Six-pack or two of their favorite libation in the box.)

I'll build myself one, but I'll scrounge for a Mil-Surplus 6" gauge that you can see a flea sneeze on - the calibration fee would be nothing compared to what they want for a new one... ($400 and up.)

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Reply to
Bruce L. Bergman

Since my pencil gauge, compressor regulator, and Milton gauge all agree, I think I'll take the really cheap way out and continue to trust the Milton gauge and just overfill by 5 PSI. ;-)

Reply to
Ray O

Does tigger not say this anymore?? is he alright???

Reply to
Stephen H

whatever it is, 25 psi is way too low. Keep it at 35 psi cold and you're always good. Right now you are using more gas, and wearing out the tires faster.

Reply to
RT

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