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Low Ambient Temp/ Tire Pressure

Discussion in 'Technical Q&A' started by UroTrash, Feb 4, 2007.

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  1. UroTrash

    UroTrash Four Time F1 World Champ
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    Jan 20, 2004
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    #1 UroTrash, Feb 4, 2007
    What effect does cold ambient temp have on tire pressure, i.e., if you check your car outside (Cold car), and it's, say, 30*F, what decrease would you expect?

    I checked my daughter's pressure, showed 30.5 PSI, door jamb calls for 32 PSI. Ambient temp about 30*. After a 4 mile trip to fill the tank for her, it showed 31.5 PSI.

    I usually run the tires a little on the hard side in her car ~34 or 36.
     
  2. MarkPDX

    MarkPDX F1 World Champ
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    #2 MarkPDX, Feb 4, 2007
    Haven't driven the Vette in a few months but it was pretty normal to see the tires two or three PSI below normal on a cold morning in TX. Even if the car was sitting outside for a while and one side was in the sun and one in the shade it was normal to see a one or two PSI split between, it balances out after driving a couple miles.
     
  3. UroTrash

    UroTrash Four Time F1 World Champ
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    #3 UroTrash, Feb 4, 2007
    Don't you expect all tires to lose 1 PSI per month naturally, regardless of ambient temp?
     
  4. BigTex

    BigTex Seven Time F1 World Champ
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    #4 BigTex, Feb 4, 2007
    A cold morning it'll set off my flat tire monitor on new Toyota truck......before driving.
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #5 Steve Magnusson, Feb 4, 2007
    Don't know the loss rate, but "yes" -- tires are not hermetically sealed devices.

    When a manufacturer says "cold", it really means "without the added heat of rotational use".
     
  6. John Harry

    John Harry Formula Junior

    Sep 8, 2005
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    John Harry
    #6 John Harry, Feb 5, 2007
    P2 = P1 * T2 / T1
    where T is expressed in Kelvins

    °K = (°F + 459.67) ÷ 1.8

    So 70°F = 294.26°K and 30°F = 272.04°K

    P2 = 34 * 272.04 / 294.26 = 31.4


    So 34 psi at 70°F would be 31.4 psi at 30°F
     
  7. UroTrash

    UroTrash Four Time F1 World Champ
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    #7 UroTrash, Feb 5, 2007
    ^^^ wow!!

    Yer a perty smart feller.

    Makes me feel like a fart smeller.
     
  8. John Harry

    John Harry Formula Junior

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    #8 John Harry, Feb 5, 2007
    Nah. Google makes anybody look smart.
     

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