First, when the Comfort Wheel is in the top position, exercising critters spin the Wheel and the Critter Cruiser remains stationary. Interactive fun begins by adjusting the Comfort Wheel into the middle position. In the middle position, you can watch your pet turn the wheel and roll their Critter Cruiser on any flat surface. By adjusting the Comfort Wheel to the lowest position, the Critter Cruiser will work directly on Kaytee's Hamtrac. Exciting pet powered exercise car for hamsters and gerbils Makes a great temporary holding area to keep your furry friend while you clean their home Pet-powered exercise vehicle for your small animal Adjustable racing wheel lets car work in 3 different ways: Stationary, mobile, or on a Hamtrac Not recommended for pet mice or dwarf hamster breeds