Setting a Tire's Pressure at One Temperature In Order To
Achieve a Specific Pressure at Another Temperature
Suppose you've just installed your winter wheel-and-snow-tire set on your car, in your heated garage. While it's 70°F inside, you want to set the air in your tires such that they're at their proper pressure during the coldest weather you typically encounter in winter driving, say, 15°F. What value do you pump them up to right now, in your heated workspace?
You could use the simple approximation of a 10F° change corresponding to a change of 1 PSI. And that's actually reasonably close, in the temperature range that we're talking about.
But if you want to get a more accurate setting, just fill in the fields below. Behind the scenes, in order to satisfy the requirements of Gay-Lussac's law, the Fahrenheit entries are converted to Rankine, their percentage change is noted, and the final results are adjusted for atmospheric pressure such that we're talking gauge values, i.e., what your tire-pressure gauge shows when you're doing the actual work. (And if you're using a typical workshop air compressor, and happen to be interested in my opinion, I've found the K-Tool KTI89001 to be an excellent combination of accuracy and ease of use, at a reasonable price).
So, if you're persnickety, too, have at it (and just click on or tab to another field, for changed entries to be acted upon):
Notes:
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Enter the temperature (°F) at which the tire is being filled, i.e., the current ambient temperature.
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Enter the temperature (°F) that you are preparing for.
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Enter the gauge pressure (PSI) that you want to achieve, after the current temperature changes to the target temperature.
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Adjust the atmospheric pressure (PSI), if necessary. The standard value for sea level, 14.7 PSI, is pre-filled.
Death Valley has a value of about 15.0 PSI, an upper Himalayan value is about 7 PSI, and Denver's pressure is about 12.1 PSI. These values will vary — but only by a few tenths — depending on temperature values.
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This is the gauge pressure (PSI) to set the tire to now, in order to achieve the target gauge pressure, once the temperature has changed from the current to the target value.
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This is the gauge pressure that the tire will read, if the tire were set to the target pressure now, and the temperature then changed to the target temperature.
Bill Pollack
January 2019
Niskayuna, NY
