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Thread: Digital gauge errors

  1. #1
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    Digital gauge errors

    I just finished a 4500 mile trip on my K1600GT and carried two digital gauges that I have been using for a few years. When I checked the tires one morning, both gauges showed psi as 16 pounds low. I put in 16 pounds and went on my way. Thereafter, I was seeing a warning sign and pressure was showing as 16 psi high. Checked the air pressure several more times and it was reading 42 psi, as book recommends.
    After arriving home I checked the tires with a third digital gauge and it showed the psi as 16 pounds too high. Used one of the trip gauges again and it showed 42. I threw one of the gauges away and replaced the battery in another and now both show the psi is 16 pounds too high. Needless to say, I feel lucky running 16 psi too high for 2000 miles in hot weather. I would never have imagined 2 gauges would both be faulty and give a wrong reading rather than not show anything when psi is too low or high. Lesson learned.

  2. #2
    Alps Adventurer GlobalRider's Avatar
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    "Digital" does not necessarily mean "accurate"...in fact no more than an "analog" tire pressure gauge.

    Not exactly compact, but then I did not buy it to use for motorcycle touring. Seeing how some will cart an electric tire pump along, maybe it isn't that bulky.

    If you want a quality gauge, have a look at those from Longacre. They are not cheap, but they are field calibrate-able and a treat to use (no leaks when the chuck is applied). Check their specs on site.

    I bought the 0-60 psi model with angle chuck, model 50394.

  3. #3
    Ed Kilner #176066
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    I'm confused a bit. When you say you saw a warning, does that mean you have continuous tire pressure monitoring on the bike? Was it consistent in what it reported? How does it stack up against the digital gauges? Why did you believe the 16 pounds low readings? That should have resulted in very flattish tires visible to the eye.

    Glad all is now well.

    And a good lesson - replace batteries before a long trip and verify proper operation afterwards.
    Ed
    2011 R1200RT Thunder Gray Metallic; 2000 Triumph 900(sold)
    http://triumphantsblog.blogspot.ca/

  4. #4
    Left Coast Rider
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    If one has on-board tire pressure monitoring, why would one not trust it? The one in my car is dead nuts accurate. On motorcycle trips, I've always carried a simple pencil gauge. Its accurate plus or minus a pound or so.

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    Administrator 20774's Avatar
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    My issue with tire pressure gages is getting the gage seated quickly and correctly for measurement. I see fluctuations in readings if I don't get the quick-on/quick-off "pffft" sound (that's a technical term! )
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    Quote Originally Posted by BC1100S View Post
    If one has on-board tire pressure monitoring, why would one not trust it? The one in my car is dead nuts accurate. On motorcycle trips, I've always carried a simple pencil gauge. Its accurate plus or minus a pound or so.
    My previous motorcycle, a Kawasaki gave inaccurate readings and this one has also been inaccurate at times so I trust my gauges more than what the TPMS says.

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    Quote Originally Posted by BMW Triumphant View Post
    I'm confused a bit. When you say you saw a warning, does that mean you have continuous tire pressure monitoring on the bike? Was it consistent in what it reported? How does it stack up against the digital gauges? Why did you believe the 16 pounds low readings? That should have resulted in very flattish tires visible to the eye.

    Glad all is now well.

    And a good lesson - replace batteries before a long trip and verify proper operation afterwards.
    Yes, the bike does have a continuous TPMS system but I have found that it is not always accurate although this time it was consistent.

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    Quote Originally Posted by GlobalRider View Post
    "Digital" does not necessarily mean "accurate"...in fact no more than an "analog" tire pressure gauge.

    Not exactly compact, but then I did not buy it to use for motorcycle touring. Seeing how some will cart an electric tire pump along, maybe it isn't that bulky.

    If you want a quality gauge, have a look at those from Longacre. They are not cheap, but they are field calibrate-able and a treat to use (no leaks when the chuck is applied). Check their specs on site.

    I bought the 0-60 psi model with angle chuck, model 50394.
    I have one of these gauges as well. I am tire gauge poor. I find the digital ones easier to use than this kind and several mechanics have recommended the digital gauges for accuracy, but I also find little difference in quality gauges.

  9. #9
    GlenFeld
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    As many have found, there is a large discrepancy in the accuracy of pressure gauges. Moderate to expansive pressure gauges are nice, but a simple drop can throw them off. In addition, if you have a gauge that allows you to also fill the tire through the gauge, that practice will alter the accuracy. I found out the hard way.

    Checking the calibration of a gauge on a regular basis is a good idea - at least you know how far inaccurate it is and you don't end up throwing it away. So, how to accurately check calibration? I haven't pulled the trigger on this yet, but plan to add a premium gauge to the air system in the shop - one that is guaranteed to be accurate +/- like a pound. Immediately next to it, add an air schrader valve. A simple press against the valve with the gauge in question, should tell how accurate the gauge in question is.

    There's details to work out, but that's an idea to allow you to easily check if the gauge is accurate or how far it's off - which is what is desired.

  10. #10
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    The cheapo Chinese analog dial gauges on ebay state +/- 2% which equates to less than 1 pound.That suits me if reliably so. I wonder how a gauge gets calibrated in the field? Seems illogical to me but then I'm no "gauge expert" for sure. We had a "instrument shop" where I once worked & they calibrated/repaired bourdon tube gauges. The real question for me is: How do you know when a gauge is on the money?
    "If I had my life to live over, I'd dare to make more mistakes next time...I'd relax,I'd limber up... I would take fewer things seriously...take more chances... take more trips...climb more mountains...swim more rivers...eat more ice cream." Jorge Luis Borges at age 85.

  11. #11
    Old man in the mountains osbornk's Avatar
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    I think we sometimes make thing overly complicated. I've tried several different kinds of gauges but I always go back to a simple pencil gauge. It has worked for me for over 50 years.
    'You can say what you want about the South, but I almost never hear of anyone wanting to retire to the North.

  12. #12
    Registered User lmo1131's Avatar
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    I always go back to a simple pencil gauge. It has worked for me for over 50 years.
    ... and it rolls up in the tool kit. My local Goodyear dealer gives me one every time I buy new tires.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
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  13. #13
    na1g
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    +1 on the simple, inexpensive, analog, pencil gauge. It takes up zero space in your tool roll or fairing storage compartment, never needs batteries and is accurate enough for all but the most obsessive.

    I carry a pencil gauge that came with a new, 1993 Concours. I compare it now and then with a small digital gauge and a large analog dial gauge, and all three agree within one PSI. Of course, they could all be equally wrong, but that seems unlikely and they match my RT's on-board tire monitor anyway.

    Happy motoring!
    pete

  14. #14
    Kbiker BCKRider's Avatar
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    This thread prompted me to check my tire gauges. Was a little shocked to find I have six! Four of them read 0 - 50 psi, two read to 100 psi, and all are the cheap pencil gauges. One 0 -50 gauge, which was checked against a new (now defunct) digital gauge, read 1.5 psi high compared to the digital gauge and so labeled. After today's little experiment, I wonder if it wasn't the digital gauge which was wrong!

    Anyway, I tried all six (twice) on the same pickup tire so any air loss from taking the reading would be minimal. The gauge marked as reading high registered 39 psi. Two of the other 0 -50 registered 40 psi, the last 41 psi. One of the higher reading gauges came in at 38, the other at 40. These readings were consistent on a second try - no change.

    As others have noted, hard to tell which is absolutely correct, but comforting to know the spread range was only 3 psi. I'm tempted to label the three which read 40 psi "accurate," the former high gauge 1 psi low, the high gauge 1 psi high. Maybe chuck the lowest reading gauge. I am a big fan of the 0 -50 psi type as they are much easier to read in the range that counts except bicycle tires - and there I've learned to trust the gauge on my bicycle pump, which is what I use to pump up slightly low motorcycle and car tires at home.

    This thread is a good reminder to check your tire gauges. Being out a pound or two is probably almost meaningless, but trusting one which is really out of whack could be bad news. So, buy a couple of those $5 0 - 50 psi cheapies and do your own check against your gauges.

    Oh yeah, the "lost air" syndrome. (I think Vonni Glaves once referred to it as changing the air in her tires!) I find it pretty easy to check the air in the rear tire with the bike on the center stand. Just be careful in centering the gauge and it shouldn't be a problem with the 45 degree angled head. Tougher on the front tire when you have double disc brakes. Pump that baby up a bit high so if you screw up a little, you are not back to the pump. There IS a technic that works - but I've forgotten it.
    Doug
    1992 K100RS

  15. #15
    Kbiker BCKRider's Avatar
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    Another thought: motorcycle and car tire pressures do move up and down a bit according to air temperature (higher temperatures bring them up) and elevation (mountain passes with thinner air decrease tire pressure.) So, if you must check your tire pressure (and have some way of increasing it,) the general advice is to do so early in the day, then forget about it, barring a flat tire. There is NO WAY a tire drops 16 pounds unless there is a puncture, which certainly leads to a flat tire.

    If my memory is correct, there are three "rule of thumb" about tire pressure: 1. a tire will lose 1 psi per month, whether in use or stored. (I find with my stored MC and summer tires for the car, they lose less than that if storage and restoration temps are similar.) 2. A tire will gain/lose 1 psi for every 10 degree F. temperature change. Certainly something to keep in mind when really cold/hot weather hits. 3. Tires lose one 1 psi for every thousand foot elevation gain, and lose it for every thousand foot decent.

    So if you are on a trip, climbing mountain passes in highly variable temps, what do you do? I suspect what most of us do is check the inflation early, set it to what we think is right (cold), and ride. Modern tires, if a little over or under inflated, are likely going to get your to destination.
    Doug
    1992 K100RS

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