I have only been to Knoxville once, but the time I was there the first heat race was best race of the night cuz track was still wet and loose , but after that race track was getting hard and what I call blue grooved, and slick. when you run 2 classes of sprint cars ( they also run a 305 class) you don"t need mods then. When I"m at TTS and see the green tractors come on to the track I SMILE cuz I know what kind of track the sprints get to run on and what kind of show I"m about to see