The Cases for and Against Primary Suspension in Truck Design

It has been held as axiomatic, almost since the inception of rail vehicles, that high speed operations demand the implementation of two-stage suspension in truck design. This paper presents factors which refute that idea. Through the analysis of both types of suspension — statically and dynamically — it is shown that the benefits that are thought to be attributable to two-stage suspensions are not confirmed by the facts. Design considerations for both single-stage and two-stage suspensions are also examined, and the non-performance issues are evaluated. It is concluded that there is no reason, from a high speed or safety performance standpoint, to implement a two-stage suspension, but that some practical — especially manufacturing — issues can dictate the use of it in certain applications. For many, if not most, applications, however, a single-stage suspension is the most desirable design choice.