For legged systems, achieving balance and locomotion depends on the system's capability to effectively and efficiently move its Center of Mass relative to its contact point(s). To measure this capability, we introduce a generalization of velocity gains: dynamic ratios which quantify this motion for passive contacts. We incorporate this generalized gain into an objective function and apply weighted matrix norms to facilitate the parameterized design optimization of 3D mechanisms. We then demonstrate the proposed approach in the design of a 3D 5-link biped across several different design objectives.