Transmission system

A transmission system for a bicycle, including:

• a system input;
• a system output;
• a chain ring;
• a set of sprockets, having varying numbers of teeth;
• a transmission unit including:
• a transmission operable according to a first transmission ratio and a second transmission ratio,
• an actuation system for switching from the first to the second transmission ratio or vice versa, arranged to switch under load, and
• a first electronically operated actuator for controlling the actuation system for switching;
• a chain driven by a chain ring for transferring torque to a selected one of the sprockets;
• a second electronically operated actuator for selecting the torque transfer from the chain to one of the sprockets for transmission of torque;
• wherein the transmission unit has an input coupled to the system input or the set of sprockets and an output arranged to be coupled to the chain ring or to the system output;
• wherein the transmission unit and the selected one of the sprockets define a system transmission ratio between the system input and the system output;
• and
• a controller configured to receive an electronic upshift signal and/or a downshift signal, and configured to, depending on the system transmission ratio in use, select which one or both of the first actuator and the second actuator to actuate for selecting the next higher system transmission ratio in response to receiving the upshift signal and for selecting the next lower system transmission ratio in response to receiving the downshift signal;
• wherein the controller is further configured to, depending on the system transmission ratio in use, select which one or both of the first and second actuators to actuate for selecting the second next, third next, fourth next or fifth next higher or lower system transmission ratio in response to receiving a further signal.