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.

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