[racer_d]

All tires experience a "heat cycle" A heat cycle is just the heating up and cooling down of a tire. Now, would you notice degradation on an all season on a camry? not likely, because neither are performance oriented. But over time (age) and use and tire composition, you might notice that the tires on the Camry are not as good in the dry at 30K miles as they were when almost new.

Lots of racers keep all types of data and keeping track of the number of heat cycles a tire is put through is one of them. They will also notice when a tire is "off" compared to a new one. Racers might use an "old" or heat cycles tire in practice, but if available, they would put on new ones (stickers) or just scrubbed in ones for a qualifying session to be a little bit quicker.

Since racers often keep so much data, they will learn that given similar conditions, a "new" tire might be several seconds per lap faster than an older tire that has been heat cycled beyond usefullness.