Which Tire Press Gauge is Right?

[OlGeezer]

I've got two air pressure gauges. One reads 33 psi one reads 36 psi. Which one is right or is neither right? How can I calibrate them? Where can I go in SoCal to find a benchmark?

 

I really never thought about this before. I have a good gauge (based on the fact it wasn't cheap). But I never questioned its accuracy. I was recently given another one, also not a cheap instrument, but the values are different. I guess I really shouldn't be surprised, but now I'm wondering which is closer and where I can go to find out.

 

Thanks,

Bill

 

[edit: put in correct forum; gave it meaningful title]

[Bob Palin]

You could just compare them with other people's at any event you go to. Or buy a third one and see which it is closest too, of course it will be in the middle

[Boffin]

A year or so ago RiDe, a British motorcyle mag, did a lab review of a dozen or so tyre pressure guages. They checked them for accuracy and repeatability. Worst performers were the cheap bourdon tube dial types, followed by pencil guages. Most digital guages were within a pound of correct, the high-end bourdon guages were within 2 pounds, but consistent. Top performer (just) was a Halfords brand 4 pounds (about 7 dollars) key-ring digital guage. I carry one of these with me everywhere these days.

The big advantage of a digital guage is the ability to self-calibrate. Trigger the measurement whilst off the tyre and it sets zero to local atmospheric, which does not vary that much (outside of hurricanes).

 

Cya, Andy

[camfarm]

I cannot answer but face the same dilemma. I took 4 pencils, 3 dials, 2 digitals and my compressor's gauge through a series of cold ambient, hot, and warm tests across my truck, trailer, bikes and bicycles. Not any agreement anywhere but a range of less than 7 psi and a consistent reading from each gauge - the errors were always the same degree in the same direction.

 

So I picked the one in the middle and feel how the ride feels.

[skinny_tom (aka boney)]

Motorcycle Consumer News just did an article about them. It turns out one of the least expensive was also one of the most accurte.

 

http://www.mcnews.com/mcn/technical.asp

 

The entire article is available in PDF format.

[upflying]

Truckers use a baseball bat as a form of tire pressure guage. By giving the tire a whack, you can get an ear for the proper pressure by listening for the bong, thump or thud.

[Boffin]

Truckers use a baseball bat as a form of tire pressure guage. By giving the tire a whack, you can get an ear for the proper pressure by listening for the bong, thump or thud.

 

Ah, so that's why you never hear of truck tyres blowing out on the freeway

 

Cya, Andy

[ednap]

I've got one of thiose little electronic ones. The garage I use to fill also has a preset filler compressor . You dial in the pressure you want (actually push buttons up or down) then it stops pumping when pressure is reached. Usually very little difference between the two and I figure a couple of PSI doesn't matter that much.

[ShovelStrokeEd]

I figure a couple of PSI doesn't matter that much.

 

Actually it matters quite a bit but you may not ride under conditions where it matters.

 

I had the opportunity to check all my tire pressure gauges against a dead weight manometer at work that is accurate to 10ths of an inch WC. Wound up I threw them all in the trash with the exception of my BMW digital tire gauge which was spot on across the range I require for tires. 30-45 PSI.

 

The pencil type gauges varied all over the map from low 5 PSI to High 6 PSI. Ditto the other two digital gauges I owned. Once cheap, one expensive. Variation between them 9 PSI.

 

I'm not a fanatic about checking tire pressures but when I do, I want to know that they are where I want them.

[Spat]

Saw the MCN article also. I was impressed one of the cheaper pencil type I always use is one of the more accurate, lucky me. What I did learn however was to keep the slide rule lubricated.

For the tires on our two wheel friends a few lbs makes a difference on tire life.

[Jerry Johnston]

I may just be getting old but, I've never been able to check tire pressure without losing a pound or two putting the gauge on the stem (or removing it - makes it hard to compare guages.

[ednap]

Good point Jerry. I just had a new tyre fitted to the front and had a right angle stem fitted at the same time. It makes it much easier to check pressure. I'll do the same for the rear when I replace it.

[OlGeezer]

I figure a couple of PSI doesn't matter that much.

 

Actually it matters quite a bit but you may not ride under conditions where it matters.

 

I had the opportunity to check all my tire pressure gauges against a dead weight manometer at work that is accurate to 10ths of an inch WC. Wound up I threw them all in the trash with the exception of my BMW digital tire gauge which was spot on across the range I require for tires. 30-45 PSI.

 

The pencil type gauges varied all over the map from low 5 PSI to High 6 PSI. Ditto the other two digital gauges I owned. Once cheap, one expensive. Variation between them 9 PSI.

 

I'm not a fanatic about checking tire pressures but when I do, I want to know that they are where I want them.

 

Congratulations, Ed.

 

You win the prize for coming the closest to actually answering my question. Based on your research, I guess what I should do is to go down to the dealer and ask to borrow a BMW digital tire gauge and then compare the results to my gauges.

 

I'm amazed how much emphasis I (and others) have put into properly inflating the tire pressure when there is little regard for the accuracy of the instrument.

 

Now, about those torque wrenches...

[dthorp29]

Where did you get the stem?

[eruff]

Ed,

 

Thanks for the great tip about the BMW digital tire gauge and how accurate it is. Because of your post, I got one today from the dealership. It was $25. It has a nice ange to it and beeps when it has a reading, sort of like electonic thermometers do. Also has auto on and auto off. Makes a good Xmas gift as well.

 

BTW, I also had the same problem as Jerry pointed out:

 

I may just be getting old but, I've never been able to check tire pressure without losing a pound or two putting the gauge on the stem (or removing it ...

Checking tire pressure is a perfect example of that physics principle "The act of observing something causes a change in the thing being observed." Is this the Uncertainty Principle? I can't be sure. Anyway, there is a solution. Elsewhere on this board someone recommended a pressure gauge to be used if you have your own compressor. You can see it here . Price is $70. If you get one, it will be one of your favorite possessions. The advantage of this gauge is that once you get the air hose on to the valve stem, you can add air by squeezing the handle and you get an immediate tire pressure reading without removing the air hose. You keep adding air until you are happy with the readout. If you overshoot your pressure reading, there is a button to bleed some pressure off. You can nail the right pressure without losing air trying to check it. So it's absolutely no stress. But is it accurate? I checked it against the BMW digital tire gauge and it both give identical readings. So, the BMW gauge goes into my tank bag for use away from home and I'll use the more expensive one in the garage to easily set the pressure before trips.

 

-Eric

[BUSTED]

Whenever you do settle on a gage, always use it. I have several but, I keep one on the bike. I always use it for the bike. Even if it's not exact, it will be consistant.

 

Years back when I did some driving, I used a 1.5lb ball pein hammer for my tire checks. Easier on the hands than a tire bat. You'd be surprised how good you get telling pressures by bounce and sound!

[ShovelStrokeEd]

Eric,

Those gauges are not really very accurate but will serve.

 

Busted,

I actually use that method more than any other. I just use my hand and give the tire a good slap. It'll ring, just so, if the tire pressure is close to right.

 

I'm still working on the conflict in tire pressures between two nearly indentical bikes. My Honda Blackbird calls for 42/42 for tire pressures. My R1100S calls for 34/36. They weigh within pounds of each other and have the same size wheels and tires, in fact, the same brand of tire. Strange.

[BUSTED]

Yes, it is something to hear that sound and know when it's right or not. As for the cycle manufacturers suggested tire pressures, they have different legal departments! I try to keep my tires happy, and the BMW factory pressures don't co-operate so, I don't use them.