EBikes work by turning on an electric motor, which propels riders faster and further compared with pedaling alone. To work properly, the brain of an eBike (called a “controller”) needs to know whether the rider is pedaling. That’s accomplished by the use of one of two common types of sensors, the cadence sensor and the torque sensor.
A cadence sensor, usually based on a magnet, sits around the bottom bracket or crankset on an eBike. As the rider pedals, the magnets pass each other, signaling the controller to turn the motor on or off. The motor turns on when you start pedaling, and stops when you stop pedaling - simple, and effective.
Cadence sensors don’t measure how hard a rider is pedaling (amount of effort), only whether the pedals are turning. This means that the system doesn’t change the amount of motor assistance based on the rider’s input - instead, the rider can control the motor using the up/down arrows on the controls to adjust the pedal assist level.
This design makes so-called “ghost pedaling” possible - by setting the pedal assist level to maximum, riders can achieve high speeds (or climb hills) while barely turning the pedals, if they so choose. As long as the pedals are turning, the motor will run.
Most value-oriented eBikes use cadence sensors, and they’re commonly paired with eBikes that use rear hub drive motors. Because torque sensing technology is more expensive, eBikes equipped with cadence sensors often represent some of the best values on the market. A cadence sensor bike can sell for several hundred dollars less than an equivalent model fitted with a torque sensor.
The Denago City Model 1.0 Top Tube and Step-thru eBike line uses cadence sensors.
Torque sensors work by measuring strain. Unlike a cadence sensor, on an eBike equipped with a torque sensor, the controller (the “brain”) knows how much rider input is being applied, and can vary the amount of power supplied by the motor accordingly. Start pedaling, and the motor turns on. Pedal harder, and the motor contributes more. Stop pedaling, and the motor turns off.
Torque sensors are commonly paired with mid-drive motors, especially those on mountain bikes intended for off-road trails.
If you're interested in an eBike equipped with a throttle, note that throttle-equipped models are less likely to be paired with torque sensors; most models featuring throttles will use cadence sensors.
Which sensor is right for my bike?
Quality eBikes can be built with both cadence and torque sensors, and there are valid reasons to choose both types. With an understanding of their capabilities, you’ll be better equipped to choose the right sensor for your needs.