Abstract: The structures and properties of Z8AG, Z8G and ZK2 bogies, as well as the problems often encountered in their operation, are analyzed. It is pointed out that the traditional three-piece bogies cannot be applied to the speed-rising of freight cars. The bogies suitable for the purpose must meet the following basic demands: the maximum running speed is at least 120 to 130 km/h, and the wearing rate and wheel/ rail contact stresses should not be larger than those of the traditional bogies.