This is one of those things where you're going to get 50 different answers. So I will add more...

At our track, we see sweep micro contacts, ions, rattlers, and now typos...all in respective clay compounds except the sweep, silver, as the popular 1/8 buggy tires. Barcodes and beams, not so much. Our track has alot of clay it so it tends to stay moist through the day.