Guessing the answer is going to be fairly simple.......

I am new to autocross, and see quite a few folks with r-compounds using a water sprayer on their tires. I assume it is to cool the tires down, but what is the benefit to this, and should it be done between every run or just after your run group is finished for the day???

 

I've seen this too. I figured it was to increase the life of the tires. I have also read that some tires (especially street tires) do not grip as well when heated.

 

Just to clarify, it's best to use tire sprayer before the temperature heats up significantly. It's easier to maintain the tire temperature while warm than bringing it down when hot. Furthermore, the shock treatment as induced by freezing/ice water or just water itself for that matter shortens the life expectancy of R-compound not furthering due to heat cycle fluctuation.

 

Refer to https://www.rx8club.com/series-i-wheels-tires-brakes-suspension-55/compound-tire-questions-70627/ for more info from previous discussion.