Jack Frost & The Cold Affect Tire Pressure

Bob Bidonde

Bob Bidonde

Well-known member
The temperature on Long Island dropped into the low 40s over this past weekend. While preparing my Victoria for a Veteran's Day Parade, I noticed the its tires looked low. Due to the dropping temperatures, the tire pressure on my "A" dropped from 32PSIG to 26PSIG, so this post is a heads-up. If the temperature has dropped in your locale, check your tire pressure.
By the way, I run Universal Tires and the label on their sidewalls indicate their maximum load rating requires 32 PSIG, not Ford's 35 PSIG. I follow the tire tire's designated pressure.
 
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It is Boyles law. P=VxT Pressure equals Volume times temperature. We live in the mountains and the temps between night and day can be over 40 degrees. Tire pressure low in the mornings and high in the afternoon. Thanks again for the heads up about tire pressure to those that do not notice.
 
Cold tire pressure vs hot tire pressure, on one of my modern car’s the door sticker for tire pressure had a cold pressure 35# and a hot tire pressure 39#. I’ve needed to check my A’s tire pressure while out and about last week I finally had a chance to check the pressure. This was after 70 mile drive, the hot pressure of 35# I added air to 39#, driving back on the same roads the car rode much softer? I believe the hard tire pressure now allowed the springs and shocks to work as they were designed !
 
Actually Boyle's Law is an extension of PV=nRT where P is absolute pressure, V is volume, n is the number of molecules in moles, R is the gas constant, and T is the absolute temperature.

Absolute zero is -460 degrees Fahrenheit. So the temperatures to compare are 75 F (535 absolute) to 32 F (492 absolute). So the absolute tire pressure would be 492/535=92.5% of the pressure at the higher temperature when it is freezing.

A flat tire still has an absolute pressure of 14.7 psi at sea level. Gage pressure is the absolute pressure minus the atmospheric pressure. A tire that reads 35 psi at sea level would read 49.7 psi in space.

This formula is what powers the car. The temperature increases during ignition.

There will be a pop quiz at 3 PM.
 
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Bob Bidonde said:
The temperature on Long Island dropped into the low 40s over this past weekend. While preparing my Victoria for a Veteran's Day Parade, I noticed the its tires looked low.Due to the dropping temperatures, the tire pressure on my "A" dropped from 32F to 26F, so this post is a heads-up. If the temperature has dropped in your locale, check your tire pressure.
By the way, I run Universal Tires and the label on their sidewalls indicate their maximum load rating requires 32 PSIG, not Ford's 35 PSIG. I follow the tire tire's designated pressure.
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:confused: :confused: How does tire pressure drop in degrees Fahrenheit?? :confused: :confused:
 
Ruth, You have to convert to absolute temperature by adding 460 to the degrees in Fahrenheit and then find the ratio by dividing one by the other. The absolute temperature scale using Fahrenheit intervals is called the Rankine scale. Here at my house it is really cold this morning, 497 degrees Rankine.
 
Oops! I goofed re temps in degrees F. Should be PSIG. Thanks for catching my error. I fixed the original post. You all are sharp!
 
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