Tire Pressure Gauge accuracy?

[larrys]

For years now I've been using my Blue Point tire pressure gauge that I bought from my local Snap-On dealer. It's one of those dial gauge units with about an 8" hose. I've always assumed that it would be accurate. I've never dropped or banged it hard.

So, just this past weekend I see that Costco is selling an Accutire brand digital tire pressure gauge for $15. I picked one up to keep in my wife's car. When I got home I opened up the new gauge and did a quick test. I checked the pressure on one of my tires and it read 30.1 psi. I pulled out my trusty Blue Point and got a reading off of the same tire of 32 psi.

Now I could understand if they were off by a few tenths of a pound. But being off by two pounds is just way to inaccurate for me.

So, how do I know which (if either) is accurate? Am I supposed to calibrate my Blue Point occasionally? If so, how?

Any ideas or suggestions?

Thanks in advance!
Larry.

[N_Jay]

Originally posted by larrys
For years now I've been using my Blue Point tire pressure gauge that I bought from my local Snap-On dealer. It's one of those dial gauge units with about an 8" hose. I've always assumed that it would be accurate. I've never dropped or banged it hard.

So, just this past weekend I see that Costco is selling an Accutire brand digital tire pressure gauge for $15. I picked one up to keep in my wife's car. When I got home I opened up the new gauge and did a quick test. I checked the pressure on one of my tires and it read 30.1 psi. I pulled out my trusty Blue Point and got a reading off of the same tire of 32 psi.

Now I could understand if they were off by a few tenths of a pound. But being off by two pounds is just way to inaccurate for me.

So, how do I know which (if either) is accurate? Am I supposed to calibrate my Blue Point occasionally? If so, how?Thanks in advance!

Any ideas or suggestions?


Larry.

I never trust a gauge to be within 2 PSI.
Two gauges will never tell you which is right.
Most people (even in performance cars) can not tell a 2 PSI difference.

[larrys]

Originally posted by N_Jay


I never trust a gauge to be within 2 PSI.
Two gauges will never tell you which is right.
Most people (even in performance cars) can not tell a 2 PSI difference.

I had first asked this question to a friend who races. His reply is that he really doesn't care too much about accuracy. He cares about consistency. He knows that he likes the performance on the track at a particular indicated pressure. If that pressure reading isn't accurate, it doesn't matter. All that matters is that its consistent.

But for normal on-street driving, being up or down a couple of pounds can make a real difference in mileage and perhaps, to a smaller degree, ride quality.

According to the knuckle-heads at Car Talk, "Under-inflated tires lowers gas mileage by 0.4 percent for every one pound of drop in pressure of all four tires." Assuming that's correct, if I would normally get around 17 mpg (pretty typical for me) then with my under inflated tires I'd only be getting less than 16 mpg.

I'd still be curious to see if there's some way to find out which is accurate or if either could be calibrated.

Maybe this is a good one to call into Click & Clack ?

Thanks!
Larry.

[N_Jay]

Originally posted by larrys
But for normal on-street driving, being up or down a couple of pounds can make a real difference in mileage and perhaps, to a smaller degree, ride quality.

According to the knuckle-heads at Car Talk, "Under-inflated tires lowers gas mileage by 0.4 percent for every one pound of drop in pressure of all four tires." Assuming that's correct, if I would normally get around 17 mpg (pretty typical for me) then with my under inflated tires I'd only be getting less than 16 mpg.

I'd still be curious to see if there's some way to find out which is accurate or if either could be calibrated.

Well get about 5 guages and have fun seeing which "appear" to be correct.

Maybe get an industrial pressure guage as your benchmark. Most are 2% of full scale, so a 50 PSI guage is good for +/- 1 PSI.

Now, let's look at the .4% MPG cange per PSI.
to make that easy, lets say it is .5%, or 1% for a 2 PSI differnce.

So if you get 17 at 36 PSI, you would get 16.83 at 34 PSI.

[larrys]

Originally posted by N_Jay


Well get about 5 guages and have fun seeing which "appear" to be correct.

Maybe get an industrial pressure guage as your benchmark. Most are 2% of full scale, so a 50 PSI guage is good for +/- 1 PSI.

If I had the funds, it could be interesting to get 5 of the same brand/model! But, not having those funds I think I'll look for a different answer .

Now, let's look at the .4% MPG cange per PSI.
to make that easy, lets say it is .5%, or 1% for a 2 PSI differnce.

So if you get 17 at 36 PSI, you would get 16.83 at 34 PSI.

Jay, please stop confusing me with the facts . I guess I'm a bit anal about this. But, I'd still like to get an answer.

Thanks!
Larry.

[N_Jay]

Originally posted by larrys
If I had the funds, it could be interesting to get 5 of the same brand/model! But, not having those funds I think I'll look for a different answer .

Don't get five of the same, they could have the same error.

Originally posted by larrys
Jay, please stop confusing me with the facts .

That's my job!

Originally posted by larrys
I guess I'm a bit anal about this. But, I'd still like to get an answer.

Yes, way too anal.

We have a hard time dealing with relative value and relative risk.
People end up worrying about the wrong things. (Back to the whole "facts" thing)

[whizmo]

Consumer Reports used to report on tire gauge accuracy, although I don't recall seeing anything recently. They considered +/- 1 psi as normal tolerances so the discrepency you're noting between your two gauges is probably within normal mfg tolerances.

If you'd like to be more accurate than this, you probably should look into gauges that cater to the racing crowd.

One thing I recall is that expensive dial guages were generally no more accurate than cheaper pencil-type gauges. In fact, one strategy I've heard is to buy 3 or 4 of a relatively cheap pencil-type gauge and throw out any gauge that is off from the others signfiicantly. This will probably net you a very accurate gauge.

I've always heard good things about this EZ-Air gauge and I like the ability to fill the tire while it remains connected.

http://www.getagage.com/

- Mark

[krygny]

I have a couple Accutire digital gauges. Both my copies are accurate within 0.2 psi. Not expensive either - <$10 on sale at Auto Zone or Auto Barn, I can never get them straight.

[N_Jay]

Originally posted by krygny
. . . Both my copies are accurate within 0.2 psi. . . .

Not to be anal about this, but how do you know?

[BigDozer66]

Originally posted by N_Jay


Not to be anal about this, but how do you know?

Probably because it says it on the package.

BigDozer66

[BigDozer66]

I wouldn't trust any of the junk tire gauges that the 'discount' auto parts stores sell.

If it doesn't have Milton on the side of it I wouldn't buy it.

http://www.amazon.com/Milton-S902-Di...210219&sr=1-42

I still have the original Milton that my dad gave me 25+ years ago when I started driving.
Every one of them has "Made in the USA" on the side of them and the quality is worth the extra money.

I think that consistency would be more important than accuracy in regards to our discussion here.

BigDozer66

[krygny]

Originally posted by N_Jay
Not to be anal about this, but how do you know?

I had them, and 3 old pencil type gauges I had laying around, checked by the calibration lab here at work. I ended up throwing away the old gauges.

[larrys]

Originally posted by larrys
For years now I've been using my Blue Point tire pressure gauge that I bought from my local Snap-On dealer. It's one of those dial gauge units with about an 8" hose. I've always assumed that it would be accurate. I've never dropped or banged it hard.

So, just this past weekend I see that Costco is selling an Accutire brand digital tire pressure gauge for $15. I picked one up to keep in my wife's car. When I got home I opened up the new gauge and did a quick test. I checked the pressure on one of my tires and it read 30.1 psi. I pulled out my trusty Blue Point and got a reading off of the same tire of 32 psi.

Now I could understand if they were off by a few tenths of a pound. But being off by two pounds is just way to inaccurate for me.

So, how do I know which (if either) is accurate? Am I supposed to calibrate my Blue Point occasionally? If so, how?

Any ideas or suggestions?

Thanks in advance!
Larry.

Well, to try to answer my question, I dropped in at Custom Alignment where I have my tires mounted & balanced and alignments done (very good shop in Mountain View, CA). They checked a tire with their very expensive (and I'm assuming accurate) gauge which read 40 psi. They then tried my Blue Point which read 39 psi. Then finally we tried the AccuTire gauge which read just over 37 psi.

So, assuming the gauge at Custom Alignment is accurate, then my Blue Point is off by a pound and the Accutire by almost 3 pounds!

I'll be returning the Accutire gauge to Costco this afternoon and stick with my Blue Point for now.

Thanks for the input from everyone!
Larry.

[N_Jay]

Originally posted by larrys
. . .So, assuming the gauge at Custom Alignment is accurate . . . .

Why?

No matter how good it was when built, it has probably undergone an extensive amount of sever use.

[krygny]

I think the accuracy of my two gauges is largely dumb luck and coincidence; and I wouldn't expect them to stay that way. But, for the price, I'm impressed.