Tire Pressure vs Temperature Calculations

[Dave W]

I'm in the process of replacing the current bolt in valve stems with some new since the existing have been there since 2015.

I did just one yesterday. The temperature was about 60F in my garage and I was using my little Porter Cable pancake compressor which tends to add some heat to the air - not much, maybe 5F. I left the tire at 80psig overnight. It's now 33 degrees currently where that tire is sitting in my garage. My accurate tire gauge says that the pressure is 75psig. In doing the calculations, that's exactly correct for the delta T change.


For those of you that have 110 psig tires, the temp delta T would have been down to 103psig. If it had been the other way, say 110psig at 60F and now after towing and the tires are at 110F, the pressure would be 122psig.

I just used this simple on-line calculator though there are more elaborate engineering level versions for those who like math: http://physics.bu.edu/~schmaltz/deflate.html..

This was kind of fun and brought back some very rusty memories from my past work life and how much easier it is now with this kind of free info now on the 'net