# Cold tire inflation pressure

• posted on November 17, 2005, 4:53 pm
My 2001 Prism specifies 30 PSI in the tires. At what temperature is this checked. Wouldn't it be different at 0° F or at 32°F or 70°F?
---MIKE---

>> (44° 15' N - Elevation 1580')
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• posted on November 18, 2005, 12:34 am
---MIKE--- wrote:

Of course the pressure changes as you would expect from Charles' Law. The 30# tire might be about 26# at 0°. Car companies expect you to check the pressure at whatever temperature you are at and adjust it accordingly. Most people don't check often enough.
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• posted on November 18, 2005, 12:39 am
"Cold pressure" refers to the typical seasonal temperature. If it's winter and the average temp is 32F, then 32F is the "cold pressure temperature". If it summer time, then than 80F might be the "cold pressure temperature". One has to adjust the amount of air in the tires as the seasons change. Add air in the winter and possibly bleeding off air as summer approaches.
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• posted on November 20, 2005, 12:35 am
I believe "cold pressure" refers to the tire being cold. When a tire is driven on it warms up, so the pressure needs to checked before the tire is driven on more then a few miles regardless of the outside air temperature.
Al

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• posted on November 20, 2005, 5:17 pm
Al wrote:

Thank you for your response. I think you missed the intent of the question. What I wanted to know is at what cold temperature to set the 30 PSI. If I set it at 30 PSI today at 40°F, then if tomorrow was 10°F the pressure would read lower (perhaps 25 PSI ?). Where I live the temperature could vary from 40° one day to -10° the next. When should I check it?
---MIKE---

>> (44° 15' N - Elevation 1580')
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• posted on November 20, 2005, 8:13 pm
see: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=1
On Sun, 20 Nov 2005 12:17:14 -0500, snipped-for-privacy@webtv.net (---MIKE---) wrote: