English: The two types of trucks found under Superliner cars. Top: a German design that, in North America, was only used with the original Superliner I cars. It was originally equipped with an air bag suspension system, but that system was soon found unsatisfactory and the bags were replaced with springs, as pictured here. Bottom: A General Steel Castings truck used with Superliner II cars. In Amtrak service, this type has also been used with Horizon cars, Viewliner cars, Surfliner and California cars, some Material Handling Cars (MHC II), and the original self-propelled Metroliner cars.