WD-40 works very well to soften the tread on race tires "slicks or dirt track tires" . completely soak the tread of the tire thoroughly then wrap the tread portion of the tire up with saran wrap. about a week later remove the saran wrap and your tread will be very sticky like a expensive soft compound race tire.shhhhhhhhh !!!
we do this on our dirt track tires all the time and will get faster lap times !!!