 trailers that roll on tracks rather than wheels), which have two idler wheels rather than a drive sprocket.There are also certain pieces of equipment, such as the Caterpillar D9 bulldozer (and numerous other Caterpillar brand bulldozers), Tucker Sno-cat and Mattracks rubber track conversion kits, which configure their tracks in the shape of a triangle, or pyramid (when viewed from the side), with the drive sprocket at the tip of the pyramid.In this configuration, there are two idler/roadwheels and one drive sprocket (as well as a number of small, load-bearing roadwheels).