In order for an e-bike’s motor to know when to turn on or off, it needs to receive a signal from the controller, and for the controller to know when to turn the engine on or off, it needs to know when the rider is pedaling into the pedals. For this purpose, all e-bikes are equipped with one of two types of sensors, either a cadence sensor or a torque sensor.
Until recently, there has been little discussion about how the two types of sensors might influence a buyer’s choice. This is because cadence sensors were almost exclusively found on e-bikes in the lower price range and torque sensors were only found on higher-priced e-bikes. That is no longer the case; As the cost of torque sensors has fallen, they can now be found on some e-bikes that cost less than $2,000. Therefore, the specification of the sensor is another factor to consider when choosing an e-bike.
Cadence sensors and torque sensors work in very different ways and their presence on an e-bike determines how the motor delivers power. This gives an e-bike one of two different personalities that the authors cite Electric bike review is explained in this article.
One type of sensor is not inherently better than another; they are just different. However, most drivers find that they develop a preference for one type of sensor over the other.
Torque vs. Cadence: What’s the Difference?
So let’s take a look at how the two different sensors work. Both sensors record the pedal movement, or more precisely the movement of the crankset, but in two different ways. We’ll start with cadence sensors because they’re simpler and easier to understand.
A cadence sensor mounts a ring of sensors (usually 12) to the part of the frame called the bottom bracket. This refers to the set of bearings that screw into the frame. There is a magnet attached to one of the crank arms that passes a sensor when rotating. Each time this happens, a signal is sent to the controller to activate or maintain the motor.
A Cadence sensor works on a binary principle: do the pedals turn or not? They must move at a constant speed to keep the motor activated, but beyond that it doesn’t matter how fast they spin. Additionally, all cadence sensors are different, but most require at least a quarter turn of the cranks to activate the motor. As long as the cadence sensor detects pedal movement, it continues to send a signal to the controller, telling the motor to do its job.
A Torque sensor is a completely different beast. Strain gauges use a torque sensor to measure how hard the driver pedals. These strain gauges can be mounted in the bottom bracket or on the frame where the rear wheel is bolted.
When the torque sensor receives a signal, it measures how large the force is and then sends that message to the controller. The controller then tells the motor how hard it should work in relation to the PAS level selected by the driver.
Since the two sensors provide different signals to the controller, the controller must work according to a different principle depending on the type of signal received. With a cadence sensor, each PAS level is set to a fixed amount of power. PAS 1 could be 20 percent of the total rated power, while PAS 5 could be 100 percent of the total rated power.
With a torque sensor, the controller works on a reverse principle. When receiving a signal from the torque sensor, the controller measures how large that signal is and then multiplies it by the amount determined by the PAS level selected by the driver. With a torque sensor, PAS 1 could deliver power at a 1:1 ratio; PAS 2 could have a ratio of 1:2 (the motor delivers twice the power that the rider produces) and PAS 4 (often called “turbo” on many e-bikes with torque sensors) could deliver power in a ratio of 1:4. For this reason, the engine’s performance constantly adapts to the driver’s effort.
