Cold vs. hot tire pressure

Thermal Equilibrium is what is at work. Cold Inflation pressure is understood to be what the tire pressure should be set at 65 degrees F for a given load. As the tire begins to rotate under load the flexing of the tire creates heat. As the air inside the tire heats it expands and pressure increases, stiffing the tire which results in less flexing and thus less heat gain. The heat will rise until the heat being added by flexing is equal to the heat be dissipated. For your cold setting at near 80lbs and an outside ambient temp "upper 70's" I would only expect to see a temp rise of less than 4lbs, so perhaps the tire is under-inflated for the load on it. You need to know what your end of axle loadings are, pick the highest, look at your tire manufacturers load tables and determine what the cold inflation pressure should be. Tire Pressures are critical to your safety and the safety of those around you, not to mention getting the most wear out of your tires. Michelin has some excellent technical support information, particularly if you look at truck tires where weight/pressures are very much critical. Never let air our of a hot tire to reduce pressure. There are temperature compensating tables that will tell you for a given temp what should a tire be inflated to. If you are running under-inflated for your weight, you risk that enough heat will build up and in turn the internal air pressure to a point that the tire will fail (explode). You see the pieces all the time along the highway with truck tires, but it can happen to any tire of any size. btw tires sitting in the sun will have higher pressures than in the shade so when starting out in the am, know that those tires are going to be higher. Good to be concerned