some might disagree with looking at the track temps, but I measure the entry and exit of the corners and half way down the straights just before race time. I've used this to gauge what pressures we want to run. I keep in mind that the higher track surface temp, the more crap is going to come up out of the asphalt....the higher the temps, the worse the oils and crude in the track come up to the surface. I've found that with the higher temps, I run a little less pressure and it gives a little more bite coming out of the corner and they seem to get grippy when you enter the corners....the lower the temps, I can run a little more pressure and get the same feeling....and it might just be that, a feeling.....but it seems to help.... but just watching the temps and you can almost see the crude coming up...specially in the corners where it seems everyone that blows up and dumps all the oil at! we race super late models, cadet, pure stock, street stock, bando's and legends, so the crap really gets put down thick when one of these blow! I also keep track of the pressure and temp of the tires immediately after a race to see how much the tires grow and what pressures came up to....this helps getting the pressures set with the growth in mind....more or less tailoring your stagger so that five laps into the feature, your going to be at your optimum stagger, inside of just letting them grow and trash your setup....
oh...forgot to add that I measure in the middle of the groove....but, then I ain't the only one walking the track and checking if I have time!!