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Tire Pressure Gauge Accuracy

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Old 07-28-2010, 05:45 PM   #1
PropJet [OP] PropJet is offline
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Tire Pressure Gauge Accuracy

Everyone knows the importance of maintaining a properly inflated tire. My question is, how do you know if the tire pressure gauge you're using is accurate?

Up until a few years ago I had never used anything other than the traditional stick-type gauges. You know, the cheap 99 cent ones you can get just about anywhere. Then one day while doing a little research, I discovered that the stick-types are not known for their accuracy. The articles I had read all suggested using a digital gauge, or a round-dial type gauge. Soon after, one of my boys gave me a digital gauge from Brookstone, and I threw all of my stick-types away. Finally, I had an accurate gauge, or so I thought.

Last summer, I decided to pick up a cheap $10 Slime digital tire gauge to keep in my glove compartment. It was digital so I figured it must be accurate, and as a bonus even displayed pressures down to the tenths. When I got home I compared it to the Brookstone digital gauge I had, and the two were a few psi different.

At this point I was confused, as I've always heard that digital gauges are supposed to be accurate. I did some more research, and ordered a Moroso round-dial gauge (I think it's this one: http://www.amazon.com/Moroso-89570-P...0362988&sr=8-3). It's supposed to be individually calibrated for accuracy to within 2%, not to mention all the articles I'd read suggested one of these types. I get it, test it against the others, and it gives me yet a different reading.

Here's why I'm looking for an answer. I recently traded in my Tacoma for a new full size truck (loved the Taco, but wanted something bigger). The recommended cold tire pressure for all four tires is 35 psi, and the max pressure is 44 psi. I'm taking it on a road trip beginning this weekend, pulling a travel trailer about 400 miles through the mountains in Colorado. Using the Moroso round-dial gauge, I get a reading of 40 psi. The Brookstone digital shows 37 psi, and the Slime digital shows 35.3 psi. If I assume the Moroso is the correct one and it turns out it is not, I'd be airing it down to what I thought was 35 psi, when in fact it would really be 30 psi, which would be underflated. If on the other hand I assume the Slime is correct at 35.3 psi and leave it alone, and it turns out the Moroso is the correct one, I'm afraid the combination of the a 10,000' gain in altitude combined with the added tongue weight of the trailer, not to mention the general expansion of air as the tires get hot while driving, will easily push the psi beyond the max of 44. Either scenario can be a dangerous one if I guess incorrectly.

Any advice or guidance as to which gauge I should believe? Supposedly I have 3 accurate gauges, yet I have a variance of 5 psi from the low end to the high end.
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Old 07-28-2010, 06:05 PM   #3
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I don't know the answer to your question. But with all your gauges, I'm pretty sure your tires are properly inflated
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Old 07-28-2010, 07:15 PM   #6
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Quote:
Originally Posted by rick View Post
I don't know the answer to your question. But with all your gauges, I'm pretty sure your tires are properly inflated
Well, that's exactly my point. They're all different, and I don't know which one to trust. If I pick the wrong one to trust, I could easily be underinflated or overinflated, neither of which is good considering I'll be at max payload pulling a trailer in the mountains.
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Old 07-28-2010, 07:28 PM   #7
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Quote:
Originally Posted by PropJet View Post
Well, that's exactly my point. They're all different, and I don't know which one to trust. If I pick the wrong one to trust, I could easily be underinflated or overinflated, neither of which is good considering I'll be at max payload pulling a trailer in the mountains.
I get what you are saying, but you might be making a mountain out of a mole hill. Safety should be your greatest concern and a +/- 3 psi deviation does not create a hazard.
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Old 07-28-2010, 07:51 PM   #9
With sufficient thrust, pigs fly just fine.
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What I do, is use the chalk method to determin propper air psi. I then note the psi with a particular gauge I have, and I use it only for the truck. Same thing for my car. Use 1 gauge for it, after I find the propper psi with chalk.
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Old 07-28-2010, 08:24 PM   #10
PropJet [OP] PropJet is offline
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Quote:
Originally Posted by chris4x4 View Post
What I do, is use the chalk method to determin propper air psi. I then note the psi with a particular gauge I have, and I use it only for the truck. Same thing for my car. Use 1 gauge for it, after I find the propper psi with chalk.
Good idea. So in other words, the reading the gauge gives is irrelevent, so long as you set the tires to that specific number.
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Old 07-28-2010, 09:34 PM   #11
With sufficient thrust, pigs fly just fine.
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Quote:
Originally Posted by PropJet View Post
Good idea. So in other words, the reading the gauge gives is irrelevent, so long as you set the tires to that specific number.
Correct.
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