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cold tire pressure

Discussion in 'Gen 2 Prius Main Forum' started by jkash, Jan 4, 2004.

  1. jkash

    jkash Member

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    After reading all the posts about tire pressure, I still have questions. I live in the west San Fernando Valley of Los Angeles. Our tempertures vary greatly during the day. It can be as cold as the 30's in the early morning, and warm up to the 70's later in the day in the winter. The summer variations are even more. I know it is recommended to check the pressure in the tires when they are cold. Does that mean checking the tires first thing in the morning when they are the coldest? What tire pressure would be best for these extremes.

    Jeff
     
    #1 jkash, Jan 4, 2004
  2. efusco

    efusco Moderator Emeritus
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    It's probably safest to check a 'cold tire pressure' at the warmest time of day and set the pressures there. You'll likely be running a bit low on pressure in the colder time of day, but that's safer than running too high.

    That said, I think it depends on what pressures you intend to run. If you intend to 'max out' at 44f/42r then I would definately do a cold pressure at the warmest time of day. If you're going to stick to factory recommended pressures then I'd probably do it at the coldest time of day since you still have a nice margin of safety upward and you'll probably run better/cooler/more efficiently with the higher pressures.
    --evan
     
    #2 efusco, Jan 4, 2004
  3. SpartanPrius

    SpartanPrius New Member

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    While in complete agreement with the Doctor, allow me to add a clarification. Once inflated, each tire will hold a mass of air that produces a relative pressure based on its temperature. This temperature can be a result of climate (gee, it was 70 this morning); or, a result of road use (just drove 10 miles with a heavy load). Do be careful about other influences, such as a cold tire reading influenced by direct sunlight on one or more tires (can add 2 PSI easy).

    So, back to my point. If you are going to do your cold reading under a 30 to 40 degree morning range, but do most of your driving in a midday 60 to 70 range, then underinflate your tires in the morning approximately 1 PSI for each 10 degree difference. For the temperature ranges cited, a reduction of 3 PSI would appear to be in order. With a little doublechecking (under cool condition: no operation for a few hours, no direct sun or hot macadam surface influences), you'll come up with the right pressure for your circumstance.
     
    #3 SpartanPrius, Jan 4, 2004
  4. ThetaSigma99

    ThetaSigma99 Junior Member

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    <div class='quotetop'>QUOTE(SpartanPrius\";p=\"1157)</div>
    This may be a silly question, but for those of us who have to drive to a gas station to fill the tires up with air, how can I ever work with the cold tire pressure, since I have to actually drive the car to the gas station?
     
    #4 ThetaSigma99, Apr 14, 2005
  5. jkash

    jkash Member

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    Measure the air pressure before you leave for the gas station. You can take it again once you are at the station to see what the difference is.
     
    #5 jkash, Apr 14, 2005
  6. DanMan32

    DanMan32 Senior Member

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    I once measured the tire cold, and after driving it. Didn't find much of a difference.
     
    #6 DanMan32, Apr 15, 2005
  7. gschoen

    gschoen Member

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    The max PSI on the sidewall is for a cold pressure. They have taken thermal expansion into account. You have to drive awhile before the tires heat up, but measuring them "cold" is to get a more consistent, constant reading.
     
    #7 gschoen, Apr 16, 2005
  8. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    driving a few miles IN MOST CASES will only have a neglible effect on tire pressure. cars in good condition (decent roads, good alignment, reasonable air pressure, proper tire for load, etc) need not worry.

    the recommended tire pressure is cold tire pressure rating, that does not mean cold ambient temperature. all max tire pressures have a HUGE amount of safety margin built into them. the vehicle should sit at least 2 hours, not in direct sunlight (differences in temps from the sun side to the shade side is significant) before measuring. the biggest reason for checking pressures cold maybe to simply start with an even slate. driving the car can cause tires to heat up unevenly thus multiplying any error in pressures when adjusting them.

    keep in mind that people in extremely hot weather are likely no more prone to tire explosions than anywhere else and underinflated tires are MUCH more dangerous than overinflated tires.
     
    #8 DaveinOlyWA, Apr 20, 2005
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