Cadence Sensors Explained

A cadence sensor counts how fast your pedals turn. It doesn't measure how hard you push.¹

Cadence means the rotational speed of the crank, given in revolutions per minute. It's the rate at which you turn the pedals.²

Cadence isn't road speed

People often mix the two up. Cadence is related to wheel speed, but it's a separate measurement. The same cadence can give different speeds and power outputs depending on the gear you've chosen.²

For an e-bike that matters. A cadence sensor can tell the controller you're turning the pedals. The source says the same cadence can give different speeds and power outputs depending on the gear.²

How the pedaling is detected

One source says instantaneous pedaling speed can be measured with optical or magnetic sensors and slotted discs.¹

Two kinds of magnetic part come up in the background reading.

• Reed switch. An electromechanical switch operated by an applied magnetic field. A magnet passing by makes it act.³
• Hall sensor. Hall sensors are used for proximity sensing, positioning and speed detection. They're solid-state devices, so they're not prone to mechanical wear.⁴

Whether a particular bike uses either of these isn't something these sources say. The maker's manual or spec sheet for your model is where you'd confirm it.

Limits the sources point out

Not every pedaling-speed sensor is equal. The single pedal crank magnets and reed switches often used for bicycle computers are slow and may give jerky motion. They also do not show the direction of rotation.¹

That second point matters for safety. The source explains that direction is needed to avoid an accidental fast backward spin of the pedals suddenly applying full power.¹

So a plain on-off pedal sensor is a simple way to say "the pedals are moving." It's less able to say how smooth the help should be.

What it means when you ride

A bike that only reads pedaling speed responds to movement of the cranks. The sources don't say how long that takes on any given bike, so check how your own model describes its assist.

Some models with a speed sensor can manage without a force sensor, since the pedaling force required rises sharply with speed.¹ That's one reason a speed-only design can still work.

For the other approach, read the torque sensor page. For a side-by-side view, see torque vs cadence.

If something seems wrong

Don't take apart a motor or a sensor housing to find out. Follow the maker's manual for your own model, and take the bike to a shop that services e-bikes. Treat it as a repair for someone trained, not a casual fix. A shop will want to know which sensor you mean.