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Electric Bike: Cadence or Torque Sensor, Which is better?

What’s better on an electric bike, a cadence sensor or a torque sensor and how do you know which one you have?  First things first, what is a cadence sensor and what is a torque sensor?.  What is their function and why do they exist?

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Before that, a quick lesson on the 3 classes of electric bikes as this is helpful in determining if your bike is cadence or torque sensored: Class 1, Class 2, and Class 3.  

Class 1, Class 2, and Class 3 Electric Bikes

Class 1 electric-bikes give pedal assistance up to 20 mph and can be used (almost) anywhere a regular analog bike can.  It is common for a Class 1 electric bike to be either torque or cadence censored depending on if they have a hub motor or mid drive motor.

Class 2 electric bikes give pedal assistance up to 20 mph.  They have the option of pedal assistance or throttle only.  Because of the throttle they are usually legally confined to surface streets and the bike lanes that line them by local law enforcement.  Check with your local jurisdiction.  California’s electric bike laws can be found here.  Check here for other states.  Class 2 electric bikes are almost always cadence censored because they use hub motors.

Class 3 electric bikes give pedal assistance up to 28 mph.  Like class 2 electric bikes, class 3 electric bikes are usually not allowed on pedestrian and off road trails.  It is common for a Class 3 electric bike to be either torque or cadence censored depending on if they have a hub motor or mid drive motor.

Back what Cadence and Torque Sensors do.

Cadence Sensors Vs Torque Sensors

For the motor to know when to give you power on a pedal assist bike, it needs to know when you are pedaling.  The pedaling sensors are divided into two groups:  Cadence and Torque.  A cadence sensor tells the motor simply if you are pedaling or not.  A torque sensor lets the motor know both when and how hard you are pedaling.

With a cadence sensor the motor is either assisting at full power or not at all.  With a torque sensor the motor will give varying levels of power based on how hard you are pedaling and what assist mode the motor is in.  Typically pedal assist electric bikes will have 3 levels of assistance:  Eco, Sport, and Boost.  Eco is the lightest level of assist and Boost is the most powerful setting.

Example

Let me give an example.  Suppose you have two pedal assist electric bikes, one with a torque sensor, one with a cadence sensor.  Both on boost mode and both have a maximum torque of 50 Nm.  Let’s say you are pedaling with 50 Nm of force.  What do you think the torque output of each motor will be?  Give up?  

For the cadence sensored motor it will give 50 Nm of torque.  The torque sensored motor will only give 20 Nm or torque.  Why the difference you ask?  

I’ll tell you.  Since the cadence sensor lets the motor know only if you are pedaling or not its force output is a constant 50 Nm.  If you pedal hard it gives 50 Nm and if you pedal soft it gives 50 Nm.  The cadence sensor always gives 50 Nm of power no matter how hard you pedal.  On the other hand the toque sensored motor will give a varying level of assistance.  In this example it assists at 20 Nm or force because it is designed to deliver 50 Nm max to the road.  It finds the difference between how hard you are pedaling and the 50 Nm max and it makes up the difference until you reach top speed.  If you were pedaling with 10 Nm of force it would contribute 40 Nm.

The cadence sensor motor has the capability of delivering more than 50 Nm of torque to the road because it is adding 50 Nm to whatever you put into it.  If you are pedaling 30 Nm and the motor is giving 50 Nm you will be getting 80 Nm total torque to the road until you reach top speed.

Which is Better?

So it sounds like the cadence sensor is better right?  More torque!  Not so fast.  As with anything the cadence sensor has its pros and cons.

Because you can get more torque to the road you will accelerate faster with a cadence sensor.  If you are a speed demon this is for you.  If you like a more natural feel, a cadence sensor will feel jumpy.  For a more natural feel you’ll want a torque sensor.  A cadence sensor will feel more like a dirtbike and a torque sensor feels more like riding an analog bike but you are built like action star Dwyane “The Rock” Johnson.  Both are fun but each feels different.

A con to the quick accelerating cadence sensor is that the battery will run out quicker.  Because the motor is always operating at full speed ahead when you are pedaling, it is always losing battery power at full speed.  On the torque sensor if it is operating at half its max, it will require less power than max from the battery, and your battery will last longer and thus the battery life and bike range will be longer.

Which one do I have?

So how do you tell if your bike is cadence sensored or torque sensored and which one is right for you?

If you have a Class 2 electric bike with a throttle you almost certainly have a cadence sensored bike.  A hub motor and a jumpy feel? You have yourself a cadence sensored bike.  If you have a mid drive motor and a natural feel you’ve found a torque sensored bike. 

In summary if you like a more natural feel and long range, get a torque sensored mid drive motor.  Rather your buddies from a dead stop and don’t mind the sorter range that comes with better acceleration, a hub motor with a cadence sensor may be right for you.

In my opinion I prefer the torque sensor because it avoids the jumpy feeling that can make the bike feel like it is driving you as opposed to the other way around.  The cadence sensor sounds exciting but in reality the feeling the torque sensored motor gives you will make you think you might be Superwoman and Lance Armstrong’s love child, and that’s pretty exhilarating!

-Brian Ahlering

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