If I remember correctly, dry air gains about 1 psi per 10 degrees temp increase. As the tires flex (tires are flat on the bottom) as you run down, the road generating heat. If the air in the tire has moisture, then the tire pressure increases much more as water vapor expands. I don't remember how much exactly. So the hotter, the tire the more pressure. Most tires are designed to run at 200 degrees F for their design life. So expect about 15 psi rise for a heavily loaded tire (somewhere near there designed max air pressure). A less heavily loaded tire will run cooler, but if you drop the pressure for a better ride, the tire will flex more and thus more heat and air pressure.
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Jim & Roy Davis
2016 Hurricane 31S
1961 Rampside in tow
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