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Thread: Pressure gauge accuracy - different front to rear.

  1. #1
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    Pressure gauge accuracy - different front to rear.

    We were endurance racing over the weekend and had problems with the rear tyre not holding up.

    A local, reputable racer who was there helping us brought along his very expensive gauge and found that while my front was accurate and was reading the same pressure as I had set with my gauge, his readout of the rear was 4 PSI higher than what I had set on my gauge.

    So for example, I had the rear set at 25 PSI but he was reading 29. The front was at 33 and was no more than 1 PSI out.

    Can gauges be affected by differences in air volume? Im perplexed as to how the front at a higher pressure could have been more accurate and the rear way off.

    I set it with an Oxford Digital Gauge. One of the swivel head ones. I also checked it with my backup gauge of similar price and it as well had the same reading.

    Has anyone experienced this?

  2. #2
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    I actually have a gauge that is inaccurate but it was reading correct on my car tire and 2 psi low when I measured my motorcycle tire pressure?! So, I guess it is possible (or at least in my experience). Compared it to my Motion Pro digital gauge.

  3. #3
    Honest always, feared often Micah / AF1 Racing's Avatar
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    There are differences in gauges but nothing like you describe have I ever experienced with a good quality pressure gauge. I do not use digital myself, just an oil filled analog, not crazy expensive but reliable and accurate for years? Number 1 reason for flase readings is forgetting to hit the pressure dump valve between checks...I know this is something I have done more than once. You also want a gauge in the correct scale for the application. I have totally different sets of similar gauges in different pressure ranges for say my cars (0-50 psi) vs truck (0-100 psi) as I run my cars in the 35-41 psi range and my truck in the 65-85 psi range.
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  4. #4
    apriliaforum expert wrx_02's Avatar
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    If your tire pressures are in the 19psi to 30psi then you want a 60psi gauge for it to be the most accurate.
    Like Micah said ( I feel like I am saying this a lot today) get a good analog one. Intercomp or I hear Montion Pro makes a decent one.
    The key with any of these no matter how good they are, is to check them for accuracy often. I usually keep 2 on hand, verify that they are correct (our tire vendor has a 25psi setup to check on) then check them against each other every race weekend. If one is off, I give Intercomp a call to get it fixed.

    Dropping the gauge, setting it in the sun all day, carrying it by the hose can all effect the accuracy over time.
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    Agree with the above... high end liquid filled gauge 0-60 PSI reading.

    I do not trust digital gauges, period.

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  6. #6
    Honest always, feared often Micah / AF1 Racing's Avatar
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    I am not in any way saying that higher end digital gauges suck, they don't. There is just something I find very comforting in a digital world about an analog gauge, when I got my newest set of Mitutoyo calipers it is not like I tossed my old sliding scale set out. Digital can be very precise, I actually use a pretty sweet digital compression tester that can store and log strokes, show peak values and do so for even checking a V12 motor in a single session usually now but, for tires, I just love the old oil filled analog gauge.
    Diminished expectations is the key to happiness in life.

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  7. #7
    apriliaforum expert Hellgate's Avatar
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    I have a lovely Motion Pro analog, liquid filled gauge with a pressure purge button. It's an outstanding gauge. I've found it consistent with the gauge on my bike pump and high end analog bicycle gauge. Either all 3 are right, or all 3 wrong!

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  8. #8
    %@*#&! hank's Avatar
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    Ah pressure gauges... use 5 different gauges (yes, even from the tire vendor) and you'll get 5 different readings...

    Do you treat it properly? Keep it out of the sun, never drop/bump it, NEVER lend it out and overall protect it from abuse? Do you treat it like the precision instrument that it is (or was when you purchased it)?

    Probably not...

    And most importantly, do you get it calibrated regularly?

    I have a box of them that I've acquired over the years... digital, oil filled, expensive, cheap - you name it...

    But I stopped that nonsense and wasting of money because the brand I continually use and recommend to everyone is Accu-Gauge - and I get them calibrated at least once every year.

    They are actually quite inexpensive and the charge for calibration is a mere $3 - and that's a single fee to recalibrate ALL of them I send back.

    https://www.ghmeiser.com/

  9. #9
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    Quote Originally Posted by hank View Post
    Ah pressure gauges... use 5 different gauges (yes, even from the tire vendor) and you'll get 5 different readings...
    Do you treat it properly? Keep it out of the sun, never drop/bump it, NEVER lend it out and overall protect it from abuse? Do you treat it like the precision instrument that it is (or was when you purchased it)?
    Probably not...
    And most importantly, do you get it calibrated regularly?
    I have a box of them that I've acquired over the years... digital, oil filled, expensive, cheap - you name it...
    But I stopped that nonsense and wasting of money because the brand I continually use and recommend to everyone is Accu-Gauge - and I get them calibrated at least once every year.
    They are actually quite inexpensive and the charge for calibration is a mere $3 - and that's a single fee to recalibrate ALL of them I send back.
    https://www.ghmeiser.com/
    um yeah ah no. Already did bench marking with their stuff against a motion pro analog.
    So the bench marks started a 5psi and then every 5 til the gauge max of 60... the accu was attrociously inaccurate at the 5-50 psi range. So much so my buddy threw his right in the trash and bought a longacre.

    If handled properly then a gauge shouldn't need annual recalibrations. Also most tire shops have a calibration source or master you can bench mark against for free.

    A rear tire reading high? Its possible if the tire was on the warmer for sometime it could have an effect on pressure.

  10. #10
    %@*#&! hank's Avatar
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    Quote Originally Posted by turboblew View Post
    um yeah ah no. Already did bench marking with their stuff against a motion pro analog.
    So the bench marks started a 5psi and then every 5 til the gauge max of 60... the accu was attrociously inaccurate at the 5-50 psi range. So much so my buddy threw his right in the trash and bought a longacre.

    If handled properly then a gauge shouldn't need annual recalibrations. Also most tire shops have a calibration source or master you can bench mark against for free.

    A rear tire reading high? Its possible if the tire was on the warmer for sometime it could have an effect on pressure.
    And I have a Motion Pro analog that is inconsistent form one measurement to the next... YMMV...

    I agree that people don't 'need' to get their gauges calibrated every year, or their suspensions serviced, chassis serviced, or torque wrenches serviced every year (or more), or change the oil every other track day.

    But I do and I'm OK with that. Again, YMMV...

    And yes, Longacre does make an excellent gauge - I have an analog one as well.

  11. #11
    apriliaforum expert NUMBER41's Avatar
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    The size of the tire and the actual temp/pressure have zero impact on the accuracy of the gage. Pressure is pressure. I could go into depth on ideal gas laws, the effect of humidity, etc. But the reality is that the delta is likely due to the accuracy of the gage. Most consumer grade gages are lucky to be accurate within 10%. Even a calibrated gage is probably only calibrated to within 5%. So, if your gage is off by 5% and your buddy's gage is off by 5%, then your 4psig delta is right in line.
    I find tinsel very distracting.

  12. #12
    apriliaforum expert meanstrk's Avatar
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    I have three gauges that I try to rely on. One is a Motion Pro liquid filled analog that was inaccurate when I first received it, but became accurate after it sat for a couple days and stabilized after poking the hole in the rubber grommet as directed. One is a Longacre analog that consistently reads 2PSI high, and the other is a China cheapo EBay digital gauge that seems to be accurate as hell.
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    Pretty funny I spent a bunch of money on tire gauges and the $3 pen type one from the gas station seems to be accurate within 1 psi LOL

  14. #14
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    Quote Originally Posted by hank View Post
    And I have a Motion Pro analog that is inconsistent form one measurement to the next... YMMV...
    I agree that people don't 'need' to get their gauges calibrated every year, or their suspensions serviced, chassis serviced, or torque wrenches serviced every year (or more), or change the oil every other track day.
    But I do and I'm OK with that. Again, YMMV...
    And yes, Longacre does make an excellent gauge - I have an analog one as well.
    the more critical the work the sooner your calibration intervals.

    But like I said... most tire stations have a test port you can check pressure accuracy.

  15. #15
    apriliaforum expert NUMBER41's Avatar
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    Quote Originally Posted by turboblew View Post
    But like I said... most tire stations have a test port you can check pressure accuracy.
    Really? Where? I've NEVER seen one, and would be keen to check my gages. That said, I subscribe to an "old racer" and tyre reading guru's trick. He basically said, it doesn't really matter what pressure you're running, to a certain degree. You're looking for a consistent pressure RISE from cold to hot. Once you have that dialed-in, then you've got pressure right, regardless of what the gage says.
    I find tinsel very distracting.

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