Cold Tire Pressure Calculation Based on Ideal Gas Law
The “Ideal Gas Law” is a formula that attempts to predict hot tire pressure based on a predicated expansion of air (from cold in our example) to a hot target temperature. I have found this formula to be somewhat helpful in determining cold tire pressure using a target hot pressure and hot temperature. It gets us in the ballpark but is not accurate enough for our needs. My default method is the regression equation below.
Cold Tire Pressure Calculation Based on Percent Gain
In analyzing the data I collected from my Healey, I found that tire pressures increased from session start to session finish at a fairly predictable percentage gain. The below formula just needs to know the target tire pressure and will calculate cold tire pressure using the percent gain. This method is pretty decent but, again, I found the regression equations below to be best.
Cold Tire Pressure Calculation Based on Regression Formula
Ultimately, in analyzing the data from my Healey I found that tire pressures increased at a fairly predictable rate (see prior formula) but there were some small differences in tire pressures as pressures rose. To clean up the data, I calculated regression equations based on the increasing tire pressure for the front and for the rear tires separately. The formula just needs the temperature of the tires and then uses that information to identify where hot tire pressures will be.
A noteworthy item is that I only use the formula just a few minutes before going out on track the first time. Tires should be shielded from the sun (I set them in the trailer).