B) Shock Absorption (“coasting” situations).

We handle only coasting situations here, since suspension issues related to pedaling and braking will be handled specifically in those sections.

A bicycle suspension may be suddenly compressed by the ground either through wheel contact with an obstacle such as a rock or from the impact of a drop-off.  In general, we believe that a widely curved rear axle path running slightly up and back is the best solution.  Tight curves, either circular or varying are generally inferior for shock absorption.  However, this deficiency may be mitigated to some degree by having the path tangent tilting backward through all or most of travel (for example, having a high main pivot, either real or virtual), as is the case in the The Rocky Mountain ETS-X70 and, substantially, the Giant NRS.  One might also find that short travel designs such as the Cannondale Scalpel do not have enough travel for this deficiency to be significant.

In the case of a drop-off, the situation is obvious.  A linear path will offer the smoothest, most consistent compliance.

In the case of an obstacle, the bump force will be up and back relative to the frame, so the initial tangent should be up and back.  The direction of the force will turn more vertical as the bike clears objects of “ride-able” size, so a widely curving path turning slightly upward should be ideal.  Experiment should determine the path incline and radius of curvature that produces the best result on average.

Rising rates benefit short travel designs, since this will allow better initial compliance, while reducing the probability of hard bottom-outs.