What an e-bike sensor does

You turn the pedals and nothing happens. Or the motor arrives late, or it shoves you forward harder than you wanted. Before you blame the motor, it helps to know what tells it to run. On a pedal-assist bike, that job belongs to a sensor.

What the sensor is for

On a pedal-assist e-bike the motor is regulated by your pedaling. One reference describes it this way: "The motor augments the efforts of the rider when they are pedaling."¹ So the bike needs some way to notice that you are pedaling. A sensor does that.

The same source says these bikes have a sensor that detects the pedaling speed, the pedaling force, or both.¹ Bike maker Gazelle puts it in similar terms. It calls torque and cadence sensors two ways that pedal-assist systems detect your pedaling and decide how much help to give you.²

That gives you the three kinds of sensing to know about:

• Speed of pedaling. This is cadence. It tells the bike you're turning the cranks and how fast.
• Force on the pedals. This is torque. It tells the bike how hard you're pushing.
• Both together. One reference lists measuring both force and speed as a third option.³

The next two pages cover each one in detail: cadence sensors and torque sensors.

The sensor doesn't work alone

A sensor only reports. It doesn't decide anything. A controller reads the report and sets how much the motor adds.

Your own choice matters too. The same reference says the power supplied also depends on the support level you pick, usually from several levels running from zero to maximum.³ Assist levels get their own page.

There's a third reading as well. The speed of the bike itself is measured at the wheel, in particular to reduce or cut the motor's power at the legally set speeds.³ That's a separate sensor from the one that watches your legs.

Working through a symptom

Start with what you notice, then narrow it down.

• Nothing happens when you pedal. Check the basics first: is the bike switched on, is the battery seated, is an assist level selected? If those are fine, a sensor fault is one possibility. Your manual's error codes are the place to look, and a dealer is the one to fix it.
• Help arrives late. Which sensor your bike has may play a part. The torque or cadence page sets out how makers describe each type.
• Help feels sudden or jerky. How the bike senses your pedaling shapes the feel, and the cadence page covers one known cause of jerky motion.
• Help feels weaker than the label says. Look at the support level, then at your gear. Both change what you feel. The assist levels page goes through it.

Don't open sealed parts or rewire anything to chase a sensor problem. Follow the manual for your own model, and let a dealer handle repairs.

Where this site goes next

Each page here takes one question and sticks to what makers and reference sources say. Where the sensor physically sits is on its own page. The legal side, where classes and pedal assist meet, is on the class limits page.