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Discussion Starter #1
When checking tire pressure in my car(s) and bike I always used cheap tire gauges that you can find in any auto parts store for a few dollars. And I always thought that they are pretty accurate.

Well, yesterday I was putting air in my wife's car tires which is equipped with tire pressure monitoring system and noticed that my cheapo tire gauge was off by anywhere between 4 to 6 psi. It was actually reading lower than the one in the car.
I tend to think that one in the car is accurate considering that it is a Mercedes, and the fault is with my own tire tool.

So, now I'm curious to find out whether I was consistently over inflating my bike tires. Will be going to auto parts store after work to get another (hopefully better) gauge.

Just thought I would share this info with you.



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Ah, but it's worse than that. Cheap (cheaply made, not necessarily price) may not only be too high or too low, but even be inconsistent on top of that.
 

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Unfortunately, more expensive isn't necessarily better...

I have the good fortune to be able to check my tire pressure gauge(s) against fairly accurate rate equipment (0.1% of reading). Sometimes you have to toss out one (or mark it with a correction factor) now and then because it's off too far. I'm currently using a basic pencil gauge from NAPA that was $4 or $5. It's within 1/2 to 1 PSI across the typical tire pressure range for my bike...well, last time I checked anyway.
 

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Discussion Starter #5
At this point I'm willing to spend few bucks, buy two or three different tire gauges and compare readings.

I understand that it may be off as well, but I should be able to come up with some kind of average error margin.



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So true...

Unfortunately, more expensive isn't necessarily better...

I have the good fortune to be able to check my tire pressure gauge(s) against fairly accurate rate equipment (0.1% of reading). Sometimes you have to toss out one (or mark it with a correction factor) now and then because it's off too far. I'm currently using a basic pencil gauge from NAPA that was $4 or $5. It's within 1/2 to 1 PSI across the typical tire pressure range for my bike...well, last time I checked anyway.
Back, before I retired from manufacturing, I too had access to precision gauges. I never found a over-the-counter device that I could trust. I ended up buying a precision gauge, that can be calibrated, and made my own out of brass fittings and NAPA parts. We often off road in a Jeep and run the tires down to 6-8 PSI depending on the surfaces we're running. This is what sent me off on this investigation. My Grandson has a digital device and it's pretty good except when it's cold outside (below 50f). The it's seems to read low and varies 2-4 pounds. $.02
 

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Somewhere I read some guy had taken a whole lot of 'garden variety' tire pressure gauges and put them on one of those gauges and had determined that the 'dial' type gauges were consistently more accurate than the 'stick' type gauges. Just food for thought. He also found that a lot of the el-cheap-o digital gauges you find for $5 were pretty close, but some were WAY off (I imagine chinese manufacturing standards aren't strict!)

Also, just FYI, just because it's a mercedes doesn't NECESSARILY mean the TPMS is accurate. It very well may be, but even the higher end cars buy components like that in bulk from the same places Ford is getting it for the sub-compact fiesta. (TPMS is required in the US now). I'm not saying it is, I'm just saying it COULD be. There are more accurate ways to test than TPMS.
 

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I think I have five pressure gauges. Three are the digital type and are within 1/2 psi of each other, one is a stick type built into a filler fitting for my air compressor which is way off,the newest, and by far the most expensive, is a dial type on a zero loss gauge I bought just to set my shocks expensive but worth every penny.
 

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Discussion Starter #9
Also, just FYI, just because it's a mercedes doesn't NECESSARILY mean the TPMS is accurate. It very well may be, but even the higher end cars buy components like that in bulk from the same places Ford is getting it for the sub-compact fiesta. (TPMS is required in the US now). I'm not saying it is, I'm just saying it COULD be. There are more accurate ways to test than TPMS.
I totally agree with you. It was just an assumption when I saw difference in readings between TPMS and tire gauge. I did expect some inaccuracies but not 4-6 psi. When I'm in the car I could live with that, but when I'm on two wheels I kinda want to make sure that tire pressure is within specs.
Right now I just don't know.

Any suggestions on a good tire pressure tool.
Thx.



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Dunno if these are still available, but about a year ago Consumer Reports rated these two digital gauges as recommended models -
Accutire MS-4400B
Accutire MS-4021B

These two pencil gauges had "very good" accuracy ratings -
Gorilla Automotive TG1
Slime 2005-A
 

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Somewhere I read some guy had taken a whole lot of 'garden variety' tire pressure gauges and put them on one of those gauges and had determined that the 'dial' type gauges were consistently more accurate than the 'stick' type gauges. Just food for thought. He also found that a lot of the el-cheap-o digital gauges you find for $5 were pretty close, but some were WAY off (I imagine chinese manufacturing standards aren't strict!)

Also, just FYI, just because it's a mercedes doesn't NECESSARILY mean the TPMS is accurate. It very well may be, but even the higher end cars buy components like that in bulk from the same places Ford is getting it for the sub-compact fiesta. (TPMS is required in the US now). I'm not saying it is, I'm just saying it COULD be. There are more accurate ways to test than TPMS.
Dial gauges are usually both more accurate and more consistent than a pencil-gauge. Dial gauges can also often be calibrated if need be. Downside is they usually take up more space, and if you have one of the "compact" ones that don't, you're probably not getting it into anywhere as difficult to reach as a rear motorcycle tire's valve stem.

TPMS is typically very accurate, and they'd better be because those sensors (or TPMs) run anywhere form $50 to $150 a pop, dependent on application. HOWEVER, most TPMs will actually read 2-3 PSI LOW from within the tire compared to a properly-calibrated tire gauge. I have no idea why, honestly. Sometimes I catch them dead on-the-money, but I've never found one reading high in comparison to a good tire gauge.
 

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Discussion Starter #13
UPDATE.
Got this digital tire pressure gauge from AutoZone Monday for about $10 bucks.
Used both, the new and the old (one on the left in the picture) to check tire pressure in my wife's car (with TPMS) and my bike.

As I suspected reading from the digital gauge was consistent with TPMS and confirmed that my old analog tire gauge is off by approximately 5 PSI, reading lower.
Here are the numbers for my Vulcan 500

------------Analog Gauge-------Digital Gauge
Front Tire-----26 PSI---------------33 PSI
Rear Tire------30 PSI---------------35 PSI

I'm fairly certain that digital gauge is accurate because I was sort of given a reference point by a mechanic at the body shop where I had my other car repaired after an accident. When I was picking my car up Saturday he said that the front tires were overinflated and he lowered it to a spec 32PSI. When I checked it with new gauge it was right on the money at 31.5 PSI.

The verdict, I was constantly over-inflating tires on my Vulcan. Don't think it would have caused any problems, but....
 

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