Like the pilot truck, trailing trucks come as pony trucks--two-wheeled, four-wheeled (and in one-case six-wheeled). The trailing truck supports the overhanging weight of the firebox and cab and must swing to the side on curves. The firebox slides from side to side on cast-steel buffer plates embedded with roller bearings inside, so its weight and the cab's is always carried by the trailing truck frame. The trailing truck smooths the engine crew's ride, as well as reducing driving axle loadings on track with weight restrictions.