Bicycle system and automatic control system thereof

A bicycle system, comprising:

• a sensing module, configured to sense a pedaling cadence and a pedaling torque of the bicycle system in a riding state so as to output a pedaling cadence signal and a pedaling torque signal;
• a control device, coupled to the sensing module and configured to receive the pedaling cadence signal and the pedaling torque signal, the control device setting a first cadence threshold and a second cadence threshold according to a preset pedaling cadence, wherein the first cadence threshold is greater than the second cadence threshold;
• a gear device, coupled to the control device and having a gear ratio;
• and
• a motor device, coupled to the control device and configured to provide an auxiliary torque, wherein a torque ratio is formed by the auxiliary torque and the pedaling torque;
• wherein the control device determines when the pedaling cadence is greater than the first cadence threshold or less than the second cadence threshold so as to set to increase or decrease the gear ratio.