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What a tire guy told me about TPMS. True or false?

Discussion in 'Other Cars' started by daniel, Nov 19, 2011.

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  1. daniel

    daniel Cat Lovers Against the Bomb

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    Yesterday I awoke to see snow on the ground, so I figured it was time to get the snow tires put on my Tesla. While I was waiting, I somehow got into a conversation about TPMS with one of the tire guys. What he told me sounded like a crackpot conspiracy theory, but since I don't know anything about it, I figured I'd ask here:

    He claimed that the ABS computer, since it knows the EXACT revolutions:distance ratio for each tire, can calculate the air pressure inside the tire. Lower pressure reduces the effective circumference. He said that before there was TPMS, there were cars that used the ABS to tell you your tire pressure, and that TPMS was introduced to sell consumers an unnecessary and expensive gadget.

    I think this is wrong, because the ABS does not know exactly how far the car travels per revolution of the wheels. Perhaps it could detect a discrepancy between different tires, but I doubt it's that sensitive, and even if it is, if all the tires are low it would look like normal to the ABS.

    Plus, it has all the hallmarks of a conspiracy theory: the idea that an entire industry has promoted a useless but expensive gadget, and that no manufacturer will use the older, "better," cheaper method. I can believe that GM would foist something useless on us to boost profit, but I think that Honda would stick with the less-expensive system if it really worked, or worked just as well.

    Can anybody shed more light on this?
     
    #1 daniel, Nov 19, 2011
  2. austingreen

    austingreen Senior Member

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    that's kind of funny. As tires wear they get smaller, different tires of the same replacement size also have different circumferences. If you had gps attached to the distance sensor, it could calculate when changes occurred more rapidly, but it would not likely alert you as fast as you would like. ABS would need to use steering and differential calculations to figure out uneven wear or deflation,and they don't do that.
     
    #2 austingreen, Nov 19, 2011
  3. xs650

    xs650 Senior Member

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    My understanding of the older cheaper simpler system is that it compared revolutions of the 4 wheels over a period of time and decided from that if a tire was going flat. The software had to be sophisticated enough to ignore wheel spin and probably some other things.

    Wiki has some info in it, it basically doesn't meet US standards

    Tire-pressure monitoring system - Wikipedia, the free encyclopedia
     
    #3 xs650, Nov 19, 2011
  4. El Dobro

    El Dobro A Member

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    Nothing new, my 2002 Buick Century monitors TP thru the ABS rather than sensors. VW was using the sensors, but went to the ABS system about a year ago.
     
    #4 El Dobro, Nov 19, 2011
  5. Rae Vynn

    Rae Vynn Artist In Residence

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    Ours figured out I had a low tire. Damn nail. Fixed now.

    I wasn't expecting a low tire on a brand new set, so I'm glad it worked.
     
    #5 Rae Vynn, Nov 19, 2011
  6. dhanson865

    dhanson865 Expert and Devil's advocate

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    1. He is right that the ABS/Traction control ECU + sensors are fine grained enough to to the work of TPMS.

    2. Doing it that way isn't as good as dedicated TPMS systems that have replaced the cheaper method

    3. Because of 2 we can clearly say it isn't a conspiracy, it's just a better technical solution.
     
    #6 dhanson865, Nov 19, 2011
  7. daniel

    daniel Cat Lovers Against the Bomb

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    Thanks for that!

    Is this the regular TPMS in your Prius? Or is this in a different car? My 2004 doesn't even have TPMS. But the Tesla gave me a warning one time and the tire was indeed low. Not low enough to show up visually yet, so it was still safe, but good to be alerted and pump up all the tires.

    I'd have the system installed in my 2004 Prius if it could be done.
     
    #7 daniel, Nov 19, 2011
  8. Rae Vynn

    Rae Vynn Artist In Residence

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    The OEM TPMS on the Prius, yes. The '07 had them standard.

    Well, I assume so. I don't think they replaced the sensors when we got new tires... those are pricey, right? ... they just put them back on when I got my new tires.
     
    #8 Rae Vynn, Nov 19, 2011
  9. JimN

    JimN Let the games begin!

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    The US law mandating TPMS was phased in starting October 2005. All US cars made after September 2007 must have a TPMS.
     
    #9 JimN, Nov 19, 2011
  10. El Dobro

    El Dobro A Member

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    Yep, just not necessarily a system that requires a pressure sensor.
     
    #10 El Dobro, Nov 19, 2011
  11. daniel

    daniel Cat Lovers Against the Bomb

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    Is a retrofit possible? Or does it require a compatible car computer? Can it be installed as a stand-alone receiver plus the sending units in the tires?
     
    #11 daniel, Nov 19, 2011
  12. El Dobro

    El Dobro A Member

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    Here's a start.
    http://www.amazon.com/Orange-Electronic-P409S-Retrofit-Monitoring/dp/B002DYH586
     
    #12 El Dobro, Nov 19, 2011
    1 person likes this.
  13. daniel

    daniel Cat Lovers Against the Bomb

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    Thanks, El Dobro!!! I'm going to get one of those. (Unless my tire place recommends a different brand.)
     
    #13 daniel, Nov 19, 2011
  14. Rokeby

    Rokeby Member

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    About two years ago when I had the OEM tires mounted on my
    powder coated rims and the TPMS sensors switched over, I had the
    opportunity to speak to the tire shop manager about TPMS.

    He was all hot and bothered about them... not that they were good or
    bad, but about the many ugly situations he anticipated when the sensor
    batteries were discharged and the sensors in need of replacement.
    There would be the cost of the units themselves and the cost of
    unmounting/remounting the tires.

    He said the batteries, which cannot be replaced, have a service life of 5
    years. He said that he was seriously thinking of leaving the business
    before 2012, when he saw a flood of customers venting their anger on
    him and not those who made them mandatory in the first place.

    As yet, I have not heard of or from anyone, here on PC or otherwise,
    commenting on the need/cost to replace their TPMS sensors. Five years
    is coming up for the earliest installed sensors...

    I guess the new year will tell.
     
    #14 Rokeby, Nov 19, 2011
  15. xs650

    xs650 Senior Member

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    On some other cars, 7+ years seems to be normal. He's right though, there are going to be a lot of unhappy people and a lot of pieces of tape to cover the TPMS warning light.

    Once they start failing en masse I think the aftermarket will provide more reasonably priced replacements for the factory sensors. It will still probably be about $100 to get all 4 done if you are already buying tires.
     
    #15 xs650, Nov 19, 2011
  16. daniel

    daniel Cat Lovers Against the Bomb

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    A hundred bucks every five years is $20 per year. That's nothing compared to the amortized cost per year of owning a car! And for the convenience of being able to see my tire pressure easily, I'm doing it in a heartbeat!

    If the batteries give out near the time for switching winter/summer, I imagine there will be no additional cost. If it's mid-season, double the above figures, and it's still worth it.

    You could just use a tire gauge regularly, but I'm a klutz and I have a hard time getting the gauge on solidly enough to get a reading without letting out so much air that I then have to pump them up again. $40 a year to avoid the hassle, for me it's a no-brainer.
     
    #16 daniel, Nov 19, 2011
  17. cproaudio

    cproaudio Speedlock Overrider

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    the 98 Sienna XLE has TPMS as standard equipment. stupid nice person tire shop replaced all the sensors with cheap valve stem. it's too late to get them back and the tire shop wont put the TPMS back.
     
    #17 cproaudio, Nov 19, 2011
  18. dhanson865

    dhanson865 Expert and Devil's advocate

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    TPMS batteries are designed for 7 to 10 years life depending on the manufacturer/brand/OEM. I'm sure there will be a few early failures but the big wave won't be until 2015.

    Besides, many will just disable their TPMS or ignore the warning light instead of complaining to the repair man.
     
    #18 dhanson865, Nov 20, 2011
  19. dhanson865

    dhanson865 Expert and Devil's advocate

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    worse than failure!

    I'd give the manager or owner a chance to correct the mistake but if they decline it'd be time for BBB, small claims, consumerist.com, local news and so on until they step up to stem the losses.
     
    #19 dhanson865, Nov 20, 2011
  20. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Stem the losses caused by the lost stems? :D

    TPMS is a commendable idea: I'm not going to tear them out of our OEM wheel/tire combo, but whenever any event comes along that would require me to make an expensive outlay to keep them functional, it won't be happening.
     
    #20 Mendel Leisk, Nov 20, 2011
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