A while back, when the temps were in the single digits, my tire pressure sensor sounded the alarm. I checked pressures and all 4 were at 27-29psi. So I increased pressure to 35psi all the way around. The other day, with temps in the high 30s to low 40s, I checked pressures again. They were all at about 38-40psi! My question is this: If your tires have the factory recommended pressure of 32psi @ 50 degrees F, at what temperature will the tire pressure drop low enough to trigger the tire pressure sensor? Similarly, if you increase pressure to 35psi during cold(?) temperatures, at what temperature will the tire pressure increase?

C-Lawd

'04 DG Coupe

 

This is out of the US Navy Diving Manual:

Charles’/Gay-Lussac’s law states that at a constant pressure, the volume of a gas is directly proportional to the change in the absolute temperature. If the pressure is kept constant and the absolute temperature is doubled, the volume will double. If the temperature decreases, volume decreases. If volume instead of pressure is kept constant (i.e., heating in a rigid container), then the absolute pressure will change in proportion to the absolute temperature.

Basically if you fill your tires to 35 psig at 50 F and the gas (not the tire) reaches 60 F, your tire pressure will be 42 psig. If the temperature of the gas drops to 40 F, your tires will be at 28 psig.



Russ

Black 6MT Coupe
Jax, FL
PS2 and Headrest Monitors Thread

 

It's not perfect, though, because the volume isn't kept constant.. the rubber tires do flex a bit and the volume changes just a little bit. Probably not enough to throw you off by more than a degree, though.

 

"Basically if you fill your tires to 35 psig at 50 F and the gas (not the tire) reaches 60 F, your tire pressure will be 42 psig. If the temperature of the gas drops to 40 F, your tires will be at 28 psig. "

Just to tell you, "absolute temperature" refers to Kelvin.

A change from 50->60 degrees F is not a 20 percent increase in the absolute temperature.. it is much less.

Just FYI

Twlight blue/Willow 6mt.
It's here

 

It's closer to 1psi per 10deg F.