E-bike sensor

All e-bike motors, from the most basic to the best available, needs a certain amount of sensor technology to function. Without the sensor, effective assistance from the motor would be impossible and your riding experience would leave a lot to be desired. Here, we explain what an e-bike sensor is, what types of sensors there are, and how they work.

What kind of e-bike sensors are there?

An e-bike sensor tells the motor when and how much assistance the e-bike rider needs. The types of sensor that e-bike manufacturers use today can be divided into three categories: 

Cadence sensor/motion sensor

A cadence sensor or motion sensor depends on your riding behaviour. A motion sensor reacts to the crank of the pedals. When the crank is moving forward, even slightly, the sensor registers this and transmits corresponding signals, starting the motor. When the rider stops pedalling, the motor also stops. 

When you start riding, the signal transmission from the cadence sensor to the motor takes a moment, so that there is a slight delay before the motor support starts. You also experience this when you stop pedalling, when you feel that the motor continues to run momentarily. 

E-bikes with a cadence sensor are well-suited for older people or people who have diminished finished muscle strength. Because of the way the sensor works on these bicycles, the bicycle only needs a little effort from the rider to start moving. This means that these sensors are a good choice for people with health issues, but also for people with an interest in efficiency. An even cadence is not only easy on the joints but also on the motor and makes for the smoothest riding experience. Depending on which gear and which assistance level you are using on your e-bike, a mid-drive motor will support different maximum speeds. 

One cautionary issue to be aware of is that when walking the e-bike, it may happen that the motion sensor starts the motor because the pedal is turning as you walk. 

Torque sensor or force sensor

A torque sensor or force sensor also measures the movement of the pedals. But this type of sensor not only responds to the pedalling cadence. It also measures the force you are putting behind your pedalling. 

By nature, whenever the pedal is at the top or bottom of the crank, there is a loss of power that would otherwise lead to continuous variance in the measurement results and fluctuating motor assistance. For this reason, the torque sensor registers both the rotation and the force being applied to the pedals. This is what gives the mid-drive motor of your e-bike the information it needs to provide the optimum assist level. When you start pedalling harder, the motor adjusts its assistance and reduces its power. If your pedalling power is lower, the motor assistance increases. This makes for the smoothest and most pleasant driving experience. But it does depend on precision programming of the motor control unit. 

Speed sensors

Speed sensors, by contrast, have nothing to do with the pedal. They measure the speed of your e-bike and are used to switch off the motor at the legally permitted maximum speed of 25 km/h (or 45 km/h for S-pedelecs). There are also speed sensors that influence the control in a more differentiated way, for example by ensuring that the motor gradually cuts out before you reach the maximum speed with your e-bike. 

Where are the sensors on an e-bike?

The various types of e-bike sensors are placed at different positions on the e-bike. 

The pedal sensor on the e-bike is located directly on the bottom bracket in the immediate vicinity of the crank in order to register the movement of the pedals. 

Torque sensors are mounted either at the dropout of the frame (the place where the rear wheel axle is taken up by the frame) or in the area of the bottom bracket. 

The speed sensor on an e-bike is located either on the spoke or directly on the brake disc mount.  

If the e-bike sensor is defective

Often, when an e-bike owner comes into the workshop with an electric bicycle suspecting a problem with the motor or drive unit, it is only the e-bike sensor that is no longer working properly. Sometimes, the problem is only a dirty sensor, and after cleaning, everything works fine again. 

It can also happen that the spoke magnet for the speed sensor has become twisted or has fallen off. This causes malfunctions in the technology and the loss of motor power.  

Fault codes that your e-bike manufacturer can read can tell you whether a major repair is needed or whether the spoke magnet on your electric bicycle is the issue. These fault codes can be found online.