Abstract: An automatic electromechanical gear changing system for automatically derailing the endless chain of a multi-speed bicycle from one rear transmission sprocket to another rear transmission sprocket to effect rear transmission gear shifting. The automatic gear changing system includes a main housing member mounted to a down tube of the bicycle, a handlebar-mounted console which displays various system parameters for the rider (type of program in use by system, speed, gear, battery level, trip miles), and a microprocessor unit disposed within the console for initiating, controlling, and terminating transmission gear shifting of the endless chain on the rear transmission sprockets.