Tyler0215 wrote:
Why did you add more air to the tires?
If the Michelin chart says 85 psi for the weight you are carrying, thats the pressure you should run. Don't be adjusting the pressure when the tires are hot.
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.
