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Tricking the tpm system...

Discussion in 'Gen 2 Prius Technical Discussion' started by SLO Cat Wrangler, Mar 10, 2008.

  1. SLO Cat Wrangler

    SLO Cat Wrangler Junior Member

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    I've got a theroitical question. Since my '08 prius has a tpm system I wanted to know if I could "trick it" to give me a low pressure warning when it drops below a set point. Here is what I mean. I want to make sure that my tires always are pretty close to the pressure I set them at. If I fill them up at 40psi (really 42 in front, 40 in the rear) and reset the monitoring system then if the drop 20% the system will let me know. I hope this is correct as I am going on this assumption. That means that they could drop to 32 psi before I would get a warning light. This seem to me to be a little low and could end up causing a decrease in my fuel economy. I would like to know a little sooner as then I could take action to increase their pressure.

    What if I put 50psi into the tires (assuming that I didn't get killed by a tire flying off the rim), reset the tpm system then backed them back down to 40psi. If the pressure drops much from 40psi won't the tpm system let me know and thus I can add a little air? Am I thinking that the tpm system is really not that sensitive or does it work a different way?

    Thank,
    Steve
     
    #1 SLO Cat Wrangler, Mar 10, 2008
  2. donee

    donee New Member

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    Hi SLO...,

    Yep, I think that might work. Its worth a try at least.
     
    #2 donee, Mar 10, 2008
  3. Bob64

    Bob64 Sapphire of the Blue Sky

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    Yes, that works and many people already use that trick :)
     
    #3 Bob64, Mar 10, 2008
  4. Boo

    Boo Boola Boola Member

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    Yes, that will work. But a couple of things:

    1. I think the warning light goes on when the pressure drops 25 percent, not 20 percent.

    2. My math skills, among other skills, have seriously declined :p So if I typically fill my tires to 42 psi front/40 psi rear, what are the exact steps I have to follow if I want the TPMS to warn me that a tire has lost 10% psi?
     
    #4 Boo, Mar 10, 2008
  5. Bob64

    Bob64 Sapphire of the Blue Sky

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    42psi *.9 = warning pressure of 37.8

    X *.75=37.8

    37.8/.75 = 50.4 psi.
     
    #5 Bob64, Mar 10, 2008
  6. SLO Cat Wrangler

    SLO Cat Wrangler Junior Member

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    So can I fill my tires safely to 50psi?

    Steve
     
    #6 SLO Cat Wrangler, Mar 10, 2008
  7. Boo

    Boo Boola Boola Member

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    Good question. I'm an idiot. But here are my two cents anyway:

    I think the max cold psi stated on the sidewall of the OEM Integrity tire is 44 psi, so you shouldn't run the tires above 44 psi. But I think that you can safely cold inflate the tires to 50 psi temporarily for the purposes of adjusting the TPMS, and then run them at 42/40 as is your want.
     
    #7 Boo, Mar 10, 2008
  8. Bob64

    Bob64 Sapphire of the Blue Sky

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    44 is not the "maximum" pressure that tires can take, otherwise they'll explode if you hit a bump and are at 42psi! The "Bursting" pressure is probably greater then 90psi.


    Edit: According to Car Talk
    "The burst pressure of a tire is about 200 psi."
     
    #8 Bob64, Mar 11, 2008
  9. apriusfan

    apriusfan New Member

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    Re: Maximum tire inflation pressure

    The maximum tire inflation pressure varies from tire to tire. It is listed on the tire sidewall as Boo mentions. I personally wouldn't inflate a tire beyond the maximum inflation pressure for any length of time even if the car isn't driven with the tires inflated at the higher pressure.
     
    #9 apriusfan, Mar 15, 2008
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