TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Interesting how tire pressure monitor works.. (Story about a flat tire)

Discussion in 'Model S: Driving Dynamics' started by hanl1, Sep 25, 2015.

  1. hanl1

    hanl1 Member

    Joined:
    Sep 2, 2015
    Messages:
    85
    Location:
    Stamford, CT
    I was lucky enough to get a flat tire this evening after 1 week of delivery. While driving I saw a warning 'Tire Pressure Very Low - PULL OVER SAFELY' so I did. I verified with my own eyes that the rear-right tire was flat and proceeded to call roadside assistance. The guy on the phone was very helpful and soon afterwards got a tow truck to deliver me a spare wheel. I could keep it for 3 days so I could either get my own tire fixed or buy a new one from Tesla (they don't do repairs apparently). I put the flat tire in my trunk and drove on.
    However, my dashboard still said that wheel has very low pressure and kept asking me to pull over. I verified that the spare wheel is good (at least visibly), but I called Tesla to ask about it anyways. Their answer is interesting - they say that it is normal and the car is not able to monitor pressure of the spare wheel. This could be a noob question but how does this work? There is something unique in each wheel that is somehow related to pressure monitoring? And the spare wheel doesn't have it so the old status didn't get reset which is why it still reports low pressure?
    The only difference I can see between the spare and original wheel is that the spare wheel is missing the center caps with the Tesla logo on it. But that should be purely cosmetic no? Any thoughts?

    Also, I am thinking about just getting it patched tomorrow, unless there is compelling reason I should buy a new one instead?
     
  2. trils0n

    trils0n 2013 P85

    Joined:
    Feb 12, 2013
    Messages:
    1,291
    Location:
    SF Bay Area
    Your wheel/tire has a TPMS sensor that is paired with the car. The new wheel/tire isn't paired, so the car isn't receiving pressure data.
     
  3. tezco

    tezco Sig P85

    Joined:
    Nov 9, 2012
    Messages:
    818
    Location:
    Colorado
    Actually, the car was receiving tire pressure data --- from the flat tire in your trunk!
     
  4. hanl1

    hanl1 Member

    Joined:
    Sep 2, 2015
    Messages:
    85
    Location:
    Stamford, CT
    Exactly as I thought.. just a bit surprised this kind of data is transmitted wirelessly.
     
  5. mwulff

    mwulff Member

    Joined:
    Jan 15, 2015
    Messages:
    348
    Location:
    Danmark
    There really isn't any other way to do it. It's pretty hard to connect a cable to a spinning wheel ;)
     
  6. martinwinlow

    martinwinlow Member

    Joined:
    Jun 18, 2012
    Messages:
    324
    Location:
    Herts, UK
    The sensor is normally part of the tyre valve and is installed in the wheel rim before the tyre is fitted. They use radio communication to the car to send the data. Some require car-specific pairing (Tesla) others do not. The battery is usually good for 5 years+ (tho quite why they can't generate their own power given all the moving around they do is a mystery to me! Coming soon, apparently)... MW

    tpms.jpg
     
  7. yobigd20

    yobigd20 Well-Known Member

    Joined:
    Oct 28, 2012
    Messages:
    5,793
    Location:
    Skaneateles, NY
    all 4 of my TPMS batteries went dead and had to be replaced, out of pocket. lasted about 2 years. each set costs $200. not cool. they should last longer than that. so this is an expense people should expect to be paying periodically...
     
  8. CHG-ON

    CHG-ON Still in love after all these miles

    Joined:
    Jun 24, 2014
    Messages:
    2,766
    Location:
    Santa Cruz Mountains, USA
    When I deflated a tire in order to reinstall my AlloyGator, the warning did not go off until the tire was almost completely out of air. I would certainly expect a warning much earlier than that, say at a 20% decrease in pressure. Not 80% or so. That seems like a big time safety issue to me.
     
  9. supratachophobia

    supratachophobia Active Member

    Joined:
    Sep 24, 2014
    Messages:
    1,978
    Location:
    Columbus, Ohio
    The thresholds are there because in a given day, the PSI can fluctuate as much as 15psi just by driving and the day warming or cooling. And the readings from the TPMS are not realtime, so as not to drain the batter faster. You probably caught it on the minimum thresholds at the max time between reading levels.
     
  10. Panoz

    Panoz Member

    Joined:
    Nov 19, 2013
    Messages:
    303
    Location:
    Colorado Springs, CO
    Noob question - what roadside service did you call? Tesla? Or AAA?
     
  11. CHG-ON

    CHG-ON Still in love after all these miles

    Joined:
    Jun 24, 2014
    Messages:
    2,766
    Location:
    Santa Cruz Mountains, USA
    Wow. I don't think I have ever seen that big of a PSI swing before.

     
  12. JPP

    JPP Active Member

    Joined:
    Feb 4, 2013
    Messages:
    1,842
    Location:
    SF Bay area, CA
    FWIW I have the FOBO Plus system installed on both of our cars (OEM 19" wheels, OEM Goodyear tires on the S85, OEM Primacy on the 70D). If the car has been parked overnight and the tires are cool (65 degrees F), I have pressures around 44.5-45.5. If it is a hot day (100 degrees F) and I have been highway driving at 70 MPH, I see tire temps up over 100 degrees F and pressures at 50.5-51.5.
     
  13. CHG-ON

    CHG-ON Still in love after all these miles

    Joined:
    Jun 24, 2014
    Messages:
    2,766
    Location:
    Santa Cruz Mountains, USA
    That's been my experience also.

     
  14. SPXMike

    SPXMike Member

    Joined:
    Oct 1, 2015
    Messages:
    82
    Location:
    La Habra Heights, CA
    Thanks for the info! I picked up my CPO P85+ Tuesday. Yay I'm a Tesla driver! Less than 24 hrs later I got a flat on the 105 in Compton. Am driving around with my flat in the trunk. Same experience. Hopefully I can get it fixed so I don't have to drop $525 on a replacement tire.
     
  15. brec

    brec Member

    Joined:
    Aug 3, 2015
    Messages:
    287
    Location:
    Reno, NV
    Tesla
     
  16. hanl1

    hanl1 Member

    Joined:
    Sep 2, 2015
    Messages:
    85
    Location:
    Stamford, CT
    Tesla
     
  17. Ajin

    Ajin Member

    Joined:
    Sep 11, 2015
    Messages:
    8
    Location:
    Raleigh, NC
    Where do you see the tire pressure info after updating to the new software???
     
  18. JPP

    JPP Active Member

    Joined:
    Feb 4, 2013
    Messages:
    1,842
    Location:
    SF Bay area, CA
    If you have a relatively recent build (about VIN 55000 or later) with the new TPMS system, you can use the roller wheels on the steering wheel to select the Status monitor (hold the wheel until you see the various choices, and roll to your choice). Those of us with older builds do not yet have support for TPMS display (...glad I have a FOBO Plus system).
     
  19. dhanson865

    dhanson865 Active Member

    Joined:
    Feb 16, 2013
    Messages:
    1,496
    Location:
    Knoxville, Tennessee
    Try setting the tire pressure in the dead of night winter time then driving to another state with hotter weather. Think snow slope to start and dry desert sunny day down below to finish.

    Rule of thumb is 10 F = 1 PSI (not mathematically accurate just easy to remember and still useful, more so than remembering PI as 3.1)

    Set your tires at 0F and drive them to the desert at 100F and that alone is worth about 10 PSI. Add on top of that the friction of driving and you'll get more than 10 PSI swing.

    Plenty of other factors for changing PSI (altitude, road temps, speed, duration of travel, alignment issues, etcetera) but it's doable.

    Personally I don't drive long enough or fast enough to see that big of a swing due to my driving but just driving a 15 mile commute at low speeds I see a better than 5 PSI swing.
     
  20. Drumheller

    Drumheller Member

    Joined:
    Jan 20, 2016
    Messages:
    92
    Location:
    Phoenix, AZ
    I ran into the same scenario with a flat time and the TPMS. I'm very surprised that this expensive of a car (P85+) does not display the actual PSI values of the tires somewhere in the controls. My 2008 Pontiac displayed that information.
     

Share This Page