[Healeys] Conclave tire pressure
bspidell at comcast.net
Mon May 24 17:50:52 MDT 2021
How does a pencil/slider-type of gauge know what the ambient pressure
is, and how does it compensate? I'm guessing it reads absolute pressure
regardless of ambient pressure; has anyone tried this 'experiment' with
one of those?
What would a Bourdon tube-type gauge, set to zero at Mean Seal
Level--good ones have a 'calibration' knob, or the needle can be reset
(I have one of those)--read at altitude without being reset (I'm
guessing less than zero)? IOW, a Bourdon-type gauge is effectively a
barometer, and will read less at altitude and give a higher
relative--not absolute--pressure if not reset to zero.
I presume the digital gauges--which I've found to be the most
repeatable, if not the most accurate--do have ambient pressure
compensation. Richard, did you reset your gauge to zero at altitude, or
do you use a digital gauge?
I did google it, from a reliable source:
This phrase: "... if tire inflation were set with a tire pressure gauge
at sea level (where the atmospheric pressure of 14.7 pounds per square
inch is used as ambient atmospheric pressure by the gauge), the same
tire pressure gauge would indicate the pressure has increased at higher
elevations where the ambient atmospheric pressure is lower"
I read this to mean the GAUGE, calibrated at Std. Temp and
Pressure--760mm of mercury at 15degC--will read inaccurately unless
reset for ambient air pressure. This is demonstrated in aircraft
altimeters, which are essentially barometers but have the addition of a
'calibration' mechanism, known as a Kollsman Window. So an altimeter,
which is a pressure gauge with a means to adjust to both altitude and
temperature needs to be adjusted quite often to give an accurate reading
ps. I'm not waging a semantics war here, I've often thought about these
things myself and would like clarification.
On 5/24/2021 4:13 PM, richard mayor via Healeys wrote:
> Sheesh. Temperature was not a factor. It was roughly the same
> temperature in Big Bear as it was in Portland when I checked the
> tires. I race cars. I know that tire pressure goes up when you
> race. I did not race the Healey before taking the tire pressures.
> This is not rocket science. Google it. Altitude affects tire
> pressure. Just like it affects the pressure in your ears.
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