What Is a Pedal Assist System (PAS)?

By definition, a pedal assist system (PAS) is the system used by electric bikes to provide additional power to the rider when pedaling. This is the opposite of a throttle-based system which you will find on electric scooters and some e-bikes. A throttle system will provide assistance when activated, but this will not correspond with the pedaling.

There are three main types of sensors for pedal-based assist:

• Cadence sensor
• Torque sensor
• Angle sensor

The cadence sensor detects pedal rotation speed and often direction. This type of sensor is almost always a part of PAS. For some people, PAS actually means a magnet-based cadence sensor.

A torque sensor measures the torque applied to the crank, or in other words: the rider’s pedaling force (how hard you are pushing the pedals).

An angle sensor replaces the cadence sensor and measures the angle of the crank (pedals) relative to the ground. This can be used to better assist the rider during the start and provide an overall better ride feeling.

A PAS involves one or more of the three sensors mentioned, the motor, a motor controller, and the battery. The motor controller receives the sensor measurements. The controller then uses the information to control how much assistance the rider needs from the motor.

The result is a riding experience where the rider needs to pedal before the motor will provide assistance. The feel of the bike depends tremendously on which of the mentioned sensors are implemented and how the motor controller algorithms are designed. Some low-end PAS bikes will only need “ghost pedaling” to enable the motor. Higher-end implementations can give a really nice feeling of simply having “stronger legs”.