From Tireman9:
"Is your TPM measuring internal tire air temperature as mine do or is it on the end of the metal valve stem which is cooling the air between the tire air chamber and the sensor at the end of the stem?
Have you calibrated your TPM?"
My TPMS uses sensors on the ends of metal valve stems, so clearly the temperatures are not going to be accurate measurements of temperature inside the tires. The purpose is to provide rate-of-change alarm. I have not calibrated my system. They don't indicate anything until I have driven a mile or so, but I should look and see how close the six temperatures show when they first come on line. At this time you would think they would be as close as they will ever get.
As for pressure, I use a good quality hand gauge (not calibrated) and take pains to get each tire exactly on 80 psi. The indicated pressures on the system are about +/- 2 psi when the system first starts up after a mile or so.
On your other question(s), I for one have no interest in seeing, understanding, or using any tire design formulas. I've already made up my mind that I will eventually upgrade to Michelin LT XPS RIBS and retire my Maxxis ST's, even though the LT's will surely indicate a lower load rating (but will exceed my 6000 lb axle rating). I'm following this thread for the information, education, and entertainment. (perhaps a sad statement about my life.....)
Full disclosure/true confession: I blew out 1 original Towmax at 10,000 miles and then had 2 leakers within 45 minutes at 16,000 miles. Full inspection at that time showed 2 more of the 6 were in poor shape with missing chunks of rubber etc. I did not pursue the failures with the tire manufacturer or anybody else, so perhaps I'm part of the problem here. OTOH, my reasoning was that I had abused the tires by routinely exceeding 65 mph. The first 4 months of use involved a major tour of the U.S. and I wasn't even aware of the ST speed restriction. I kept a really close eye on the pressures, but when the rest of the traffic was running 80+ on those long desolate runs out west I would typically set the cruise control to about 73 mph. Now I know better.
I was planning to upgrade from the TowMax tires to LT's but was caught short with two flats and an hour before the local tire shop closed. The Maxxis tires were the expeditious solution and apparently they are pretty good so it's not a huge disaster. They will be kept at 80 psi and they won't be abused like the TowMax tires were. I hope my tires and these discussions last a long, long time.
Thanks to all participants for your efforts!
