Bicycles are disclosed which include a rear wheel suspension system. The rear wheel suspension of the present bicycles are designed to move an instant center to track a chain torque line of the bicycle and generally improve performance of the bicycles. In certain embodiments, the rear wheel suspension system includes a shock absorber apparatus attached to the main frame of the bicycle. In additional embodiments, the shock absorber apparatus includes a bell crank or a rotary torsion spring. Embodiments are also described which include a gear box. Methods of improving bicycle performance by tracking a chain torque line with an instant center are also disclosed.