WoodIsGood wrote:
I added air as I believed (and still believe) that they were heating up excessively and didn't want to overheat and damage $2K worth of brand new tires.
Michelin's chart lists the minimum pressure for a given carry capacity. Adding 10 psi just made the volume of air in the tires roughly the same as if I'd started the trip at 95 psi (the sidewall listed max cold pressure). By the time I was rolling down the highway again the pressures were all at or below what they were when I stopped (because the tires had cooled down some). And they continued to drop slightly until settling in at about 108-110psi. In the morning they were all within 2psi of 95psi (verifying my above claim about air volume). I equalized pressures to 95 before resuming my trip.
Thermodynamics is a pretty solid science. At 80-95psi a 10* increase in temperature results in a roughly 2psi increase in tire pressure (at 30-35 psi starting pressure the same 10* increase in temperature results in a roughly 1psi increase in tire pressure). Since the hubs and brakes weren't heating the wheels (yes, I checked them for excess heat) the source of the heat for the air inside the tires had to be from the rubber. And the rubber had to be at least as hot as, if not hotter than, the air inside the tires. And based on the applicable thermodynamic equations, the air was around 250*. That just sounds too darned hot to me.
Be careful making statements like that, the 'tire pressure posse' will show up! LOL.
It's rather surprising the numbers of people who take those pressure charts as gospel and will go so far as describing 'miraculous' improvements in ride and handling by doing so.
The other issue is that as you mentioned tire heat is very much related to pressure. That heat is also very related to tire failure. If you develop a slow leak while rolling down the road, the lower the starting point, the sooner the tire will reach a critically overloaded and overheated point and fail.
