I have seen a number of references to ultrasonic air leak detectors. Do they work and would anyone happen to have an idea as to what range of frequencies they are scanning?

Also, I have seen a number of dicussions of members using IR thermometers for checking the temp of their tires. So, if you have a hot tire, what are the things that cause it to heat up above normal? I understand friction from running low. Does a bad bearing, or other such problem in the wheel cause an increase in the temperature of the tire?