A bicycle assembly can include a bicycle frame having a main frame and a sub-frame, and a shock absorber assembly. The shock absorber assembly can comprise a shock absorber and an extension body. The sub-frame can rotate in relation to the main frame and the shock absorber assembly can be used to regulate that relationship. An eccentric insert positioned functionally between the shock absorber and extension body can be used to modify the overall length of the shock absorber assembly to beneficially alter the geometry of the bicycle frame.