We are just past the 90-minute mark and the race opening stints of the American Le Mans –Monterey have been completed.

ALMS teams are required to start the race using three of the four tires used during qualifying. While virtually all of the GT teams qualified on their softest compound tires, a few may have chosen to change either a right front or a left rear tire to a medium or even a harder compound for the start. Why? Those two corners of the car take the heaviest use on the hilly, counter-clockwise, 11-turn 2.238- mile circuit.

Michelin tire engineers and their rivals from three other tire makers are regularly taking pyrometer measures of the air and track surface temperatures. The air temperature was 74 degrees at the 1:30pm race start. The track temperature was 90 degrees. Engineers expect the ambient temperature to increase by at least 8-10 degrees under the clear, sunny skies of the Monterey Peninsula.

The key numbers are time and track temperature. If the track temperatures reaches 100-110 degrees Fahrenheit, expect to see some teams switching to their medium or even hard compounds for much of the six-hour race.

As the race progresses into the late afternoon and early evening the sun moves beyond the nearby hills and puts more of the track into shade. The air temperatures will drop to the high 50’s.

The big questions are how quickly the track will cool and when. At some point, a switch back to soft tires becomes viable. The timing of that switch may well determine the winner.