Actually, I do have an infrared thermometer that I keep in my car and I do use it to check various parameters on the car. When I do this test on my car with the thermometer every brake disc is almost exactly ambient temperature.
I initially got the thermometer because I thought it would have a few uses on the car. Now, there seems to be countless uses for it. For me, I think it was money well spent.
A couple of years ago, on my 325e bimmer, following a brake pad change, the caliper was rubbing so hard that after 1 mile of driving I could smell the brake burning smell from inside the car. Needless to say, the car pulled very heavily, and all was well after a caliper replacement.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record