Electric assist bicycle and drive system of the same

A drive system for an electric assist bicycle, the drive system comprising:

• a sensor that detects a pedaling force applied to a pedal from a rider;
• an electric motor that outputs a drive power to assist a pedaling motion of the rider;
• and
• a controller configured or programmed to calculate an assist ratio provided by the electric motor;
• wherein
• the controller includes a plurality of control modes for the electric motor, including a first mode and a second mode having different assist ratios, and determines whether or not a mode change condition is fulfilled in which the mode change condition is defined as a mode change from the first mode to the second mode;
• and
• the controller performs the mode change from the first mode to the second mode when the pedal is located between a first angular position that follows by 45 degrees a lowermost position of a locus of the pedal and a second angular position that precedes by 45 degrees the lowermost position.