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Thread: Query about cheap TPM caps

  1. #1
    Registered marching ant Antaeas's Avatar
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    Query about cheap TPM caps

    While at a NAPA store, I bought some valve caps that indicate tire pressure by showing green, yellow or red behind a clear cover. It seemed like a bargain Tire Pressure Monitor system, until I noticed a flat front tire while riding one day. I found that the clear cover of the valve cap had broken off, and the air had escaped. I don't know when or how, but, after I ran my portable pump to get enough pressure, I found a plain old metal valve cap in my parts bag, and limped to a service station where I re-inflated my tire to full pressure. It has stayed inflated ever since. There was no harm done this time, but I am suspicious about these valve caps. Has anyone had a similar experience?
    Antaeas

    2005 R1200RT (Artie)

    "Can I move? I'm better when I move." - Sundance Kid (by Wm. Goldman)

  2. #2
    Benchwrenching PGlaves's Avatar
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    Quote Originally Posted by antaeas View Post
    While at a NAPA store, I bought some valve caps that indicate tire pressure by showing green, yellow or red behind a clear cover. It seemed like a bargain Tire Pressure Monitor system, until I noticed a flat front tire while riding one day. I found that the clear cover of the valve cap had broken off, and the air had escaped. I don't know when or how, but, after I ran my portable pump to get enough pressure, I found a plain old metal valve cap in my parts bag, and limped to a service station where I re-inflated my tire to full pressure. It has stayed inflated ever since. There was no harm done this time, but I am suspicious about these valve caps. Has anyone had a similar experience?
    I had a similar experience. Less severe, but similar. To sample the pressure they hold the reliable Schrader valve open - and then they themselves leak. I kept having low tires. I took the caps off - threw them out - and never regretted it one bit. I don't need an accessory that causes my tires to lose air.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  3. #3
    Mars needs women! 35634's Avatar
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    Usually the valve cap just keeps dirt away from the schrader valve. The pressure
    gauge type cap hold the valve open to monitor the air pressure, hence
    they can be the weak link in the tire's integrity. I avoid them like the plague.

  4. #4
    Registered marching ant Antaeas's Avatar
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    TPM follow-up query

    Do the pricey TPMs that are advertised in the ON also operate by holding the valves open?

    For example, see

    http://www.doranmfg.com/motorcycle-t...tm#360msensors
    Antaeas

    2005 R1200RT (Artie)

    "Can I move? I'm better when I move." - Sundance Kid (by Wm. Goldman)

  5. #5
    Republic of Texas
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    Quote Originally Posted by antaeas View Post
    Do the pricey TPMs that are advertised in the ON also operate by holding the valves open?
    Without seeing the TPM diagram, logic would indicate that if the TPM pressure sensor is inside the tire (i.e., on the pressure side of the Schrader valve) then the Schrader valve stays closed to hold air pressure in the tire. Conversely, if the TPM is on the non-pressure (atmospheric) side of the Schrader valve (i.e., screwed onto the valve stem), then the Schrader valve in the valve stem would have to be "held open" for the sensor to "see" the tire pressure.
    Mike White
    MOA Life Time Member #57882
    '13 K1300S "30 Years", '95 R1100RS, '88 K75S, '97 Ducati 916, '95 Ducati 900SS CR. Gone, but not forgotten, '75 R90S

  6. #6
    Curmudgeon At Large Bobmws's Avatar
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    I expect when the day comes I can no longer bend over to check my tire pressure, I'll no longer be riding........
    Bob Weis
    '04 K12RS - Hannigan Hack
    www.earplugco.com

  7. #7
    Rally Rat
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    Quote Originally Posted by Bobmws View Post
    I expect when the day comes I can no longer bend over to check my tire pressure, I'll no longer be riding........
    Really? 'Cuz at that point I'll be buying a sidecar rig and start going to full service gas stations, and have the attendant check tire pressure for me!

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