Pressure loss in cold weather

Discussion in 'Cycling Equipment' started by Joel Roth, Dec 4, 2003.

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  1. Joel Roth

    Joel Roth Guest

    How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?

    I recall from high school physics: Pressure * Volume/Temp, but what is is the volume of a road tire
    or a mountain tire? and what's the equation for PSI into metric units? I can figure out the
    temperature in metric units.

    Thanks

    joel
     
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  2. In article <[email protected]>, joel roth
    <[email protected]> wrote:
    >How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?
    >
    >I recall from high school physics: Pressure * Volume/Temp, but what is is the volume of a road tire
    >or a mountain tire? and what's the equation for PSI into metric units? I can figure out the
    >temperature in metric units.
    >

    You don't care about volume in this case since it won't change (so your equation becomes
    P1/T1 = P2/T2).

    Temperature must be in an absolute unit, but either Kelvin (C + 273) or Rankine (F + 459) will work
    fine. You can leave the pressure in
    PSI for either temperature.

    So a tire that is 120 PSI at 70 F will be 112 PSI at 35 F.

    --
    Bill
     
  3. joel roth wrote:

    > How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?

    Not enough to worry about.
     
  4. Bruni

    Bruni Guest

    Just remember to use Kelvin as you are comparing absolute temps.

    --
    Bruni Bicycles "Where art meets science" brunibicycles.com
    410.426.3420 joel roth <[email protected]> wrote in message
    news:[email protected]...
    > How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?
    >
    > I recall from high school physics: Pressure * Volume/Temp, but what is is the volume of a road
    > tire or a mountain tire? and what's the equation for PSI into metric units? I can figure out the
    > temperature in metric
    units.
    >
    > Thanks
    >
    > joel
     
  5. Jobst Brandt

    Jobst Brandt Guest

    Joel Roth writes:

    > How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?

    In the days of tubulars, that we had to pump daily due to their thin latex tubes, cold weather was a
    blessing of sorts because they didn't leak down as fast. I'm not sure how large the effect was but I
    recall when it was cold on trips in the Alps that we could get along fine with pumping every second
    day. That was a while ago though.

    Jobst Brandt [email protected]
     
  6. B.C. Cletta

    B.C. Cletta Guest

    [email protected] (Bill Pemberton) wrote in message news:<[email protected]>...
    > In article <[email protected]>, joel roth
    > <[email protected]> wrote:
    > >How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?
    > >
    > >I recall from high school physics: Pressure * Volume/Temp, but what is is the volume of a road
    > >tire or a mountain tire? and what's the equation for PSI into metric units? I can figure out the
    > >temperature in metric units.
    > >
    >
    > You don't care about volume in this case since it won't change (so your equation becomes P1/T1
    > = P2/T2).
    >
    > Temperature must be in an absolute unit, but either Kelvin (C + 273) or Rankine (F + 459) will
    > work fine. You can leave the pressure in
    > PSI for either temperature.

    'absolute' pressure not 'gauge'; add 15-psi. be sure to stand outside & wait about an hour or so to
    let the tire temperatures stabilize. you have to hold the bike tires off the ground to keep the
    ground contact, snow?, from influencing the results. oh yeah, you have to pump up the tires
    rrrrreeeeeaaaallllll ssssslllllloooooowwwwww to keep the heat of compression from altering the
    results. again, best done outside so you don't pump indoor air, hot & humid, into the tube. done
    over a hour or so might be OK. of course, once you start riding, the cord flex will heat the tire to
    possibly dangerously high pressures so don't overdo it. you might want to ride real slow and stop to
    check the pressure a few times, every 5 minutes or so over the first couple of hours sounds pretty
    good to determine any heating trend.
     
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