The ST and TR models come with YOUR CHOICE of the Type I or Type II tracks. NT, PT and PR models come with Type II Tracks ONLY.
The knobby Type I track is more of a bouncy ride on flat surfaces, especially on concrete. However, their design (with the knobs in the center) allows for more durability in slippery or sticky types of terrain (like red clay, mud or wet snow).
The grooved Type II track is a smooth ride, with reduced bouncing or jarring on concrete. Most types of terrain are easily traversed … you should have no issues on sand, mud, ice, dirt, gravel, grass, rocks, etc. However, the grooves may fill up with wet snow or red clay or mud and decrease traction.
Trackchair ST, Trackstander TR, Trackchair STSx