[Healeys] Conclave tire air pressure change trivia

Bob Spidell bspidell at comcast.net
Mon May 24 09:36:42 MDT 2021

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
> *From: *richard mayor <mailto:boyracer466 at gmail.com>
> *Sent: *May 24, 2021 9:28 AM
> *To: *Healeys <mailto:healeys at autox.team.net>
> *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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