Abstract: A gear shifting system for a human-powered chain- or belt-driven vehicle includes a wheel speed sensor, a cadence sensor, a gear changer position sensor, a tension sensor, a clinometer, a controller and a gear changer actuator. The wheel speed sensor senses a speed of a wheel, while the cadence sensor senses a drive rate that a torque drive member drives a torque-transmitting member. The gear changer position sensor senses a position of a gear changer that positions the torque-transmitting member with respect to a plurality of gears. The tension sensor senses a tension of the torque-transmitting member that is transmitting a torque applied to the torque-transmitting drive member to a gear. The clinometer senses an inclination of the vehicle. The controller generates a control signal based on the sensed wheel speed, the sensed torque-member drive rate, the sensed torque-transmitting member tension, the sensed vehicle inclination and the sensed gear changer position.