Change tire pressure in the cold??

[Matt_]

Oh it works.

 

[Zembonez]

Oh it works.

Not at my house.

 

[66nova]

You're not running Nitrogen in your tires on the Accord are you Jim?

 

[Zembonez]

Nope. We've always kept everything at 35 psi. The 20s on the truck all read 27-28 pounds when it dropped to 40 and the accord barely dropped at all. None were below 33.

 

[Matt_]

Nitrogen will change with temp too.... lol its a law.

Giving Jim benefit of the doubt. ... it could be because tire volume is not constant... and pressure will change with volume. As volume decreases pressure increases. The smaller volume tires probably have a higher percentage volume loss which could offset the pressure loss a bit

 

[Matt_]

Dbl

 

[Zembonez]

Nitrogen will change with temp too.... lol its a law.

Giving Jim benefit of the doubt. ... it could be because tire volume is not constant... and pressure will change with volume. As volume decreases pressure increases. The smaller volume tires probably have a higher percentage volume loss which could offset the pressure loss a bit

I have to agree that it isn't scientifically sound Matt. I understand that. I have seen it over and over though. For some reason smaller tires don't lose as much in the cold as larger truck tires. I was wondering if it might have something to do with the fact that tires are flexible "bladders" of air instead of a hard preset volume item like a steel tank. The flex of the case may not be constant.

Perhaps we should contact Obama and get some money for a case study

 

[Nick The Great]

http://en.wikipedia.org/wiki/Ideal_gas_law

I don't remember a whole lot from the Physics and Chem classes, but isn't pressure a function of Temperature and Volume?

So if temperature goes DOWN, doesn't that equation say that pressure goes DOWN. And if volume gets BIGGER, the pressure gets SMALLER

 

[buckshot85]

Nitrogen will change with temp too.... lol its a law.

Giving Jim benefit of the doubt. ... it could be because tire volume is not constant... and pressure will change with volume. As volume decreases pressure increases. The smaller volume tires probably have a higher percentage volume loss which could offset the pressure loss a bit

wanna takes my physics class

 

[Matt_]

http://en.wikipedia.org/wiki/Ideal_gas_law

I don't remember a whole lot from the Physics and Chem classes, but isn't pressure a function of Temperature and Volume?

So if temperature goes DOWN, doesn't that equation say that pressure goes DOWN. And if volume gets BIGGER, the pressure gets SMALLER

Yeaup.

lower temp = lower pressure
With tires, lower pressure = lower volume
lower volume = higher pressure

So with that in mind... i guess Jim isn't completely crazy . I haven't messed with enough car tires side by side truck tires to compare... when we had a car it was always parked in the garage. But i could definitely see a smaller car tire having more volume loss for a given pressure change than a big truck tire; this would therefore make the effective pressure loss for a given temperature less than what is seen in the comparative big truck tire.

But i'll stand by my original stance that its not proportional

wanna takes my physics class

No but you can pay me to tutor you. Between that and my "shop" in my garage im pretty good and bringing in some mod money