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Re: [Healeys] Conclave tire air pressure change trivia

To: healeys@autox.team.net
Subject: Re: [Healeys] Conclave tire air pressure change trivia
From: Bob Spidell via Healeys <healeys@autox.team.net>
Date: Mon, 24 May 2021 08:36:42 -0700
Delivered-to: mharc@autox.team.net
Delivered-to: healeys@autox.team.net
References: <CAKkXjqMZWaWYV4X7zXNU3GmDtLR1E0VTyBi7p+PW5LiZ+UMSWQ@mail.gmail.com> <DM6PR17MB2507BA238E145706046CEAC9D1269@DM6PR17MB2507.namprd17.prod.outlook.com>
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I for one can't think of an explanation for this startling phenomenon. 
Obviously, the ambient air pressure is less at altitude--known as 
'adiabatic lapse rate' to nerds and pilots--which, theoretically could 
cause the tires to expand, increasing their volume and lowering the 
pressure (according to the Ideal Gas Law). But, I doubt steel-belted 
radial tires expand or contract much, but air pressure in fixed volume 
goes up about 1psi per 10degF IIRC.

Was there a 40degF difference in temperature between Portland and Big 
Bear (California has been pretty warm the last few weeks, which I can 
attest to since our A/C is on the fritz)? Also, temps vary when tires 
are warmed by the sun or friction with the road, so if I can't check 
pressure completely in the shade I'll under-fill the tires in the sun by 
half a degree. So, my guess is a significant difference in air temps, 
and asphalt absorbs a lot of heat which gets transferred to the tires 
(Portland = (often) cloudy and cool; SoCal = (often) sunny and hot).


On 5/24/2021 8:20 AM, Jean Caron via Healeys wrote:
>
> Sounds like you have one of those rare wheels with self-adjusting 
> pressure, I wonder when these became an option and on what model 
> !!!!!! LOL!
>
> Jean
>
> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for 
> Windows 10
>
> *Sent: *May 24, 2021 9:28 AM
> *Subject: *[Healeys] Conclave tire air pressure change trivia
>
> My Healey tire pressures went from 29 psi here in Portland, Oregon, to 
> 33 psi at Big Bear Resort in California - 6,700 feet above sea level.  
> I then lowered my tire pressures to 29 psi.
>
> Checked my tires today back in Portland - 70 feet above sea level and 
> all tires at 25 psi.
>
>


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    I for one can't think of an explanation for this startling
    phenomenon. Obviously, the ambient air pressure is less at
    altitude--known as 'adiabatic lapse rate' to nerds and
    pilots--which, theoretically could cause the tires to expand,
    increasing their volume and lowering the pressure (according to the
    Ideal Gas Law). But, I doubt steel-belted radial tires expand or
    contract much, but air pressure in fixed volume goes up about 1psi
    per 10degF IIRC.<br>
    <br>
    Was there a 40degF difference in temperature between Portland and
    Big Bear (California has been pretty warm the last few weeks, which
    I can attest to since our A/C is on the fritz)? Also, temps vary
    when tires are warmed by the sun or friction with the road, so if I
    can't check pressure completely in the shade I'll under-fill the
    tires in the sun by half a degree. So, my guess is a significant
    difference in air temps, and asphalt absorbs a lot of heat which
    gets transferred to the tires (Portland = (often) cloudy and cool;
    SoCal = (often) sunny and hot).<br>
    <br>
    <br>
    <div class="moz-cite-prefix">On 5/24/2021 8:20 AM, Jean Caron via
      Healeys wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:DM6PR17MB2507BA238E145706046CEAC9D1269@DM6PR17MB2507.namprd17.prod.outlook.com">
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        <p class="MsoNormal">Sounds like you have one of those rare
          wheels with self-adjusting pressure, I wonder when these
          became an option and on what model !!!!!! LOL!</p>
        <p class="MsoNormal"><o:p> </o:p></p>
        <p class="MsoNormal">Jean</p>
        <p class="MsoNormal"><o:p> </o:p></p>
        <p class="MsoNormal">Sent from <a
            href="https://go.microsoft.com/fwlink/?LinkId=550986";
            moz-do-not-send="true">
            Mail</a> for Windows 10</p>
        <p class="MsoNormal"><o:p> </o:p></p>
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          style="mso-element:para-border-div;border:none;border-top:solid
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          <p class="MsoNormal" style="border:none;padding:0cm"><b>From:
            </b><a href="mailto:boyracer466@gmail.com";
              moz-do-not-send="true">richard mayor</a><br>
            <b>Sent: </b>May 24, 2021 9:28 AM<br>
            <b>To: </b><a href="mailto:healeys@autox.team.net";
              moz-do-not-send="true">Healeys</a><br>
            <b>Subject: </b>[Healeys] Conclave tire air pressure change
            trivia</p>
        </div>
        <p class="MsoNormal"><o:p> </o:p></p>
        <div>
          <div>
            <p class="MsoNormal">My Healey tire pressures went from 29
              psi here in Portland, Oregon, to 33 psi at Big Bear Resort
              in California - 6,700 feet above sea level.  I then
              lowered my tire pressures to 29 psi.<o:p></o:p></p>
          </div>
          <div>
            <p class="MsoNormal">Checked my tires today back in Portland
              - 70 feet above sea level and all tires at 25 psi.<o:p></o:p></p>
          </div>
        </div>
        <p class="MsoNormal"><o:p> </o:p></p>
        <p class="MsoNormal"><o:p> </o:p></p>
      </div>
      <br>
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    <br>
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