A gear shifting system for a bicycle, which gear shifting system comprises: a controller; an electromechanical gear shifter in communication with the controller; and a performance sensor in communication with the controller; wherein said controller comprises: an input parameter receiver for receiving an input parameter from said performance sensor; a threshold determiner for receiving an input value or range for said input parameter, for determining if a threshold has been met and/or exceeded, and for outputting a threshold determination; a comparator for comparing said input parameter and said threshold determination determined by said threshold determiner; and a signal generator in communication with said electromechanical gear shifter and for generating a signal based on the comparison performed by the comparator for controlling said gear shifter; and said performance sensor is adapted to indicate one or more performance measure of a rider of the bicycle and said controller is adapted to trigger electromechanical shifting of said electromechanical gear shifter in order to maintain a preset performance measure for the rider; characterised in that said controller further comprises a stabilization time delay circuit that, in use, suspends further controller action on said gear shifter for a predetermined amount of time to allow said input parameter to adjust based on a recent gear change. a controller; an electromechanical gear shifter in communication with the controller; and a performance sensor in communication with the controller; wherein said controller comprises: an input parameter receiver for receiving an input parameter from said performance sensor; a threshold determiner for receiving an input value or range for said input parameter, for determining if a threshold has been met and/or exceeded, and for outputting a threshold determination; a comparator for comparing said input parameter and said threshold determination determined by said threshold determiner; and a signal generator in communication with said electromechanical gear shifter and for generating a signal based on the comparison performed by the comparator for controlling said gear shifter; an input parameter receiver for receiving an input parameter from said performance sensor; a threshold determiner for receiving an input value or range for said input parameter, for determining if a threshold has been met and/or exceeded, and for outputting a threshold determination; a comparator for comparing said input parameter and said threshold determination determined by said threshold determiner; and a signal generator in communication with said electromechanical gear shifter and for generating a signal based on the comparison performed by the comparator for controlling said gear shifter; and said performance sensor is adapted to indicate one or more performance measure of a rider of the bicycle and said controller is adapted to trigger electromechanical shifting of said electromechanical gear shifter in order to maintain a preset performance measure for the rider; characterised in that said controller further comprises a stabilization time delay circuit that, in use, suspends further controller action on said gear shifter for a predetermined amount of time to allow said input parameter to adjust based on a recent gear change.