Abstract: Based on dynamics theory of multi-body systems, a nonlinear mathematical model of frame-bogies with Lenoir damper for freight cars is established. A tank car is taken as an example to study the effects of main parameters on hunting stability, dynamic curving behaviors and running responses of vehicle systems. It is shown that the dynamic behaviors of a freight vehicle can be improved greatly by optimization and balancing of the parameters of the bogies. For the bogies concerned, the critical hunting speed can be raised, without deteriorating the performances on curved lines, by properly increasing the stiffness of the axle-box suspension and the friction torque of side bearing, as well as reducing the longitudinal clearance of side bearings.