Abstract: A tool for unscrewing a bicycle chain sprocket from a bicycle sprocket cluster which can be used for roadside emergency repairs is disclosed. The tool has a hook which engages a portion of the bicycle frame, and a length of engagement chain which engages teeth of a sprocket to be removed. Preferably the hook engages the chain stay of the bicycle frame, and torque is applied to the sprocket cluster by the conventional driving chain. To improve mechanical advantage, the driving chain passes around the largest sprocket of the sprocket cluster, and the smallest sprocket of the chain wheel, and force is applied to the pedals at a mid-sweep position.