Bill,
I would think there are several variables to determine a "standard" tire temperature. I would say ambient temperature, traffic conditions, tire type, air pressure, weight, etc. would all have something to do with it. I use a laser type thermometer and regularly check the tire temperature and hub temperature at each fuel stop. I would say a key indicator of a problem will be a noticeable temperature differential between the tires at any given time.
It saved me big time, at one stop I noticed that my rear trailer tires were considerably hotter than the front tires. Sure enough both rear tires had low pressure and not noticeable from just looking at them. Each tire had a different issue. One has a small tear near the outer tread and the other was leaking from the rim. I did an internet search and a tire shop that was two miles away was open and it was Palm Sunday. I carry two spares, but did not want to do the rest of my trip without a spare, so I bought two new tires.
Hope this helps,
Mike Rizzo
