English: Animation, depicting the workings of a Christie-type suspension on a center roadwheel for a tracked vehicle as shown in Christies Patent US1836446A. The roadwheel (3) is mounted on one side of an "L" shaped crank, whos other side is connected to the vehicles hull (1). When the wheel is pushed up by an obstacle, the helical spring (2) is compressed. The Spring pushes the arm back down again, as soon as the load on it is reduced / the obstacle has been passed. Based upon Christie´s drawings filed for patent in April 1928.