Your going to need to be more specific still, unless you just want a general outline of how different tire compounds will respond on a hard clay track (of which there are many different types). Basically the more grip the track has the harder a tire compound you can use, since the tire will wear very quickly on a high traction surface, don't expect tread life to be any longer because its a harder rubber. If its a really low grip track (usually a bit dusty) then your going to want to go with something softer so you can regain that grip. Temperature can have a small effect on offroad tires as well, if its really cold (like near freezing) you will probably have to go with a softer tire. If the clay is really really smooth a tire with a tiny pin like a holeshot or Werks Stub will work good, but if its rutted more/coarse usually a tire with a taller pin is better, like a crime fighter or Werks Lugz. Best thing to do is to ask the fast guys what they are using. I have found that on pretty much any really hard track the Werks Lugz are the tire to use, they hook up good on a wide variety of hard pack, plus they have really good wear characteristics.