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Accuracy of TPMS?

Discussion in 'Model S: Driving Dynamics' started by COrental, Oct 16, 2015.

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  1. COrental

    COrental Member

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    I checked the TPMS display today and all 4 sensors were reading about 5 psi lower than the reading on what I think is a pretty good quality gauge. Has anyone else compared their readings?
     
  2. CHG-ON

    CHG-ON Still in love after all these miles

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    I just corrected my pressure two days ago. The fronts show as right on, the rears looked a pound or two low. That's all. I'll get them all perfect tomorrow when the tires are cold and then test. I think I have a good gauge, but have now way of truly confirming that.
     
  3. Law&Disorder

    Law&Disorder Member

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    I posted on another thread about the new vehicle status app displaying tire pressure about 4-5 psi low compared with a good quality tire gauge. It's going to become a problem for those of us in climates that are going to be getting colder soon. Should be an easy fix with the next software upgrade.
     
  4. supratachophobia

    supratachophobia Active Member

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    I don't see where to check tpms, did every car get the feature with v7?
     
  5. Barry

    Barry Member

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    I just had my tires rotated and the tech added a few lbs of pressure, to 50, as measured by his digianl inline gauge (at Firestone). TPMS shows 48, so not too bad.
    DOn't foget the tire pressure changes about 1 PSI for every 10 degrees F, if you're not checking both ways at the same time.
     
  6. JPP

    JPP Active Member

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    FWIW I compared pressures on my wife's S70D in the status display with the FOBO Plus readings--within 1/2 PSI (close enough for government work, maybe not Mil Spec...).
     
  7. thimel

    thimel Member

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    I set all 4 of my tires to 50 PSI with an accurate guage. First TPMS readings were 50, 49, 49, 49. Difference is quite small in my opinion and could be either my guage or the TPMS.
     
  8. UBQP

    UBQP Member

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    2 lbs low

    My TPMS measures about 2 or 3 lbs less than my gauge does.
     
  9. Tdriver

    Tdriver Member

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    MY 85D pressures are right on. You guys who are seeing a big difference should have your gauges checked against a local tire shop.
     
  10. gzerninplatz

    gzerninplatz Member

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    My Fobo, hand-held gauge, and TPMS pressures are the same, mostly - sometimes shows a pound different, but that could be just a smidgeon either side of the breakpoints....
     
  11. green1

    green1 Active Member

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    I'm uncertain, I have 3 cheap gauges I don't trust much, but they all agree exactly at 45psi while the car says all the tires are 40psi.
    On the one side, I trust the fancy TPMS more than any of those gauges, but at the same time, the other 3 all agree despite being horribly cheap gauges, I'm not sure which to believe...
     
  12. AWDtsla

    AWDtsla Active Member

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    3-5psi high reading here. Will have to confirm with a 3rd pressure gauge, but I've not known my existing inflation gauge to be off by that much before. Is there re-calibration for the TPMS pressure?
     
  13. boonedocks

    boonedocks Member

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    Have 21" setup and have the rear tires at 1.5 lbs higher (tpg) than the front and the on-board show same. Once the tires are warmed up they are mostly the same psi as the fronts are a little warmer than the rear.
     
  14. wizputer

    wizputer Member

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    Also seeing markedly higher reading from TPMS
     
  15. Soolim

    Soolim Member

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    Accurate to 0.1 bar
     
  16. AWDtsla

    AWDtsla Active Member

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    I had to recalibrate my filler gauge, the TPMS and a handheld digital gauge are within 0.5 psi, unless that is a coincidence, but the digital gauge zero's before measurement so it's probably OK.
     
  17. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    Few of us have the equipment necessary to determine the accuracy of our gauges; I do what AWDTsla does, but the naked truth is that all such devices could be equally wrong.

    Nevertheless -
    Creating a device to respond to relative gas pressures is not, as it's fun to say in these forums, rocket science. As such, if one has three or even two pressure gauges that agree with each other, there is an excellent chance they are correct.

    All of this brings to mind Joe Pesci's and Marisa Tomei's characters in My Cousin Vinny:

    Lisa: [sighs] If you will look in the manual, you will see that this particular model faucet requires a range of 10 to 16 foot-pounds of torque. I routinely twist the maximum allowable torquage.
    Vinny Gambini: Well, how could you be sure you used 16 foot-pounds of torque?
    Lisa: Because I used a Craftsman model 1019 Laboratory Edition Signature Series torque wrench. The kind used by Caltech high energy physicists. And NASA engineers.
    Vinny Gambini: Well, in that case, how can you be sure THAT's accurate?
    Lisa: Because a split second before the torque wrench was applied to the faucet handle, it had been calibrated by top members of the state AND federal Department of Weights and Measures... to be dead on balls accurate!
    [She rips a page out of a magazine and hands it to him]
    Lisa: Here's the certificate of validation.
    Vinny Gambini: Dead on balls accurate?
    Lisa: It's an industry term.
    Vinny Gambini: [tosses paper away] I guess the ****** thing is broken.
     
  18. green1

    green1 Active Member

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    But here's the rub, three cheap analog gauges (2 of the simple pen style slide-out ones, and one that is part of the filling assembly on my air compressor) all agree at one number, the 4 TPMS sensors all agree at a different number 5psi different...

    I'm inclined to believe the TPMS, but it does lead one to think...
     
  19. CHG-ON

    CHG-ON Still in love after all these miles

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    I have read that some see their TPMS reading a few pounds less than their tire gauge. So I did the most simple test. I filled my tires to exactly the spec for my car, very carefully, with what I think is an accurate gauge (according to tons of Amazon reviews...). 38 front, 40 rear. I then drove just far enough to get the sensors to report (less than 1/4 mi) on a very cool day with no sun on the road and slowly. They gave the exact same reading as my gauge. I was actually quite surprised. However, when I bled my tires dry in order to put AlloyGators on, the alarm did not go off until they were essentially completely flat. So I don't trust their ability to warn me that I am low, only that I am flat, which is WAAAAY too late. What's up with that? My '06 Acura would warn after a 10% drop in pressure. So I check the widget regularly. I will say that the tires don't seem to lose pressure except when the temp changes significantly. I expected that they would.
     
  20. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Modern tires with oxygen-tight butyl tubeless liners don't lose pressure unless the liner is damaged or there is a leak somewhere else (wheel or valve).
     

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