I would have to say the dirt that is at Thunder Alley in Cali and then the dirt at The NITRO PIT in Arizona. Thats my likes for 1/8. Now this is going back about 15-17 years ago there was a indoor track in Sacramento CA that used to host the Motor Man race and that was the best dirt ever they used the clay from the Sacramento River and some other things combined. The track felt like walking on a water bed and the traction was just amazing.