Originally Posted by OldCoot
I'll stick with TST/Michelin recommendations just to be safe. Will stop and let the tires cool if they get over 110° - 115° just to be on the safe side.
I think you are being over cautious, but that's OK if you want. The temperature reading of external TPMS will be lower than the internal air due to cooling of air in valve stem. Also the air in the tire will be sort of an "average" of the hot and cool surfaces of the air chamber.
As a tire engineer, I know that different rubber compounds will "revert" i.e. de-vulcanize and get soft at temperatures ranging from 200°F to 250+°F but since different areas of a tire can have 40 to 50°F different temperatures there is no way for you to know which compound is at what temperature.
I know that one TPM Mfg uses 156°F as their warning temperature. It is also true that tires will run 20°F to 60°F above ambient so again no simple one number fits all answer as your personal load, inflation, speed and tire design will give different results than I see.
BUT my experience is that I run about 20°F above ambient at 62 mph but my tires are underloaded for their inflation pressure.
I write a blog on RV tire application and safety. RVTireSafety.com
Also give seminars on tires at RV events across the US. 40 years experience as tire design & quality engineer for major tire mfg. Freelander 23QB on Chevy chassis is my RV