Optimal Tire PSI When Running

Bruce H. wrote:
My ST 215/75R14 Maxxis M8008 tires are set to 50 psi cold in the morning. I know that tire pressure increases roughly 1 psi for every 10* increase in ambient air temp as the day heats up. I also know that tire flex while running generates heat; for example, TireRack ran some tests on car tires in their lab and found that tire flex contributes 4 psi.

Typically, my TST tpms indicates that the tire on the shade side of the trailer will be running at 55-56 psi and the sun-side tire 1-2 psi higher. However, on a recent trip, the tires' cold psi of 50 had been set when the temp was 53*, and as we got into 90*+ ambient temp, the sun-side tire got up to 60 psi. As we get into summer and 100*+ ambient temps, I can see the tires going above 60 psi.

My question: is there an upper psi threshold I need to be concerned about? How much psi is too much when running? Is there an optimal running psi range I should try to stay within?

Looking forward to some knowledgeable responses.

Bruce

Bruce,

As a general rule, you want the pressure buildup to be less than 10% of the starting pressure. If you exceed 15%, you should take immediate action - typically adding pressure. Between 10% and 15% you need to consider what possible future action should be taken, but you don't need to react immediately. (But don't put off the decision for more than a few days of operation.)

So in your example, your 53 psi starting point could go as high as 58 or 59 before your should be concerned. If you add 4 psi because of the difference in ambient, then the pressure could be as high as 63 psi. So it sounds like you are OK.