Tire trivia of the day!

[Luke'sScreenName]

Ok here's a tire physics question I need help with:

My trailer tires are ST235/80R16. If it is 0 deg Fahrenheit and I inflate the tire to 80psi...

What is the pressure in the tire when the ambient temperature becomes 60 deg Fahrenheit?

Assume sea level. How about tire compliance?

 

[orezok]

Rule of thumb is 1# per 10 degrees.

 

[3930dave]

orezok's # seemed familiar.... went to see what tirerack listed....

"The rule of thumb is for every 10 Deg Fahrenheit change in air temperature, tire pressures will change about 2% (up with higher temperatures and down with lower). This means that light-duty, standard-pressure tires (typically inflated to 30-50 psi) used in applications on cars, vans and light trucks will change by about 1 psi; where heavy-duty, high-pressure tires (typically inflated to 80-100 psi) used in applications on recreational vehicles, busses and trucks will change by about 2 psi."

So.... looks like with an LT class, closer to 2# per 10F.

Rgds, D.

(If you like crunching #s, I'd say this falls under PV = nRT. Never looked at tires at that level, so don't know the specific coefficient to use with an LT class).

Edit - included a link for the tirerack page I got that info from, but when you click on it, they post a full page shopping ad, with a manual redirect link (for what I wanted to post) at the bottom. I'd rather not post the link - it's easy enough to search for.... D.

 

[Johnny g]

Rule of thumb is 1# per 10 degrees.

1 lb up or down per 10°?

 

[3930dave]

1 lb up or down per 10°?

Both.

Temperature goes up, pressure goes up. Same for down.

Rgds, D.

 

[Johnny g]

Both.

Temperature goes up, pressure goes up. Same for down.

Rgds, D.

Got it,:thumbsup:

 

[Luke'sScreenName]

Great info. Yes I was headed toward ideal gas law but didn't know how to factor for the tire's compliance. :confused3:

I the 2%/10degF is probably based on actual data and probably more accurate than the 'mental gymnastics' I had in mind!