Torque Sensors on Electric Bikes

October 18, 2012

A torque sensor is a type of throttle that determines how much juice to feed the motor based on how hard the rider is pedaling. This is different from a cadence sensor which measures simply how fast you are pedaling. Cheap cadence sensors are what can be found on most pedal assist system (PAS) bikes on the market today.

When done right, a torque sensor can make you feel bionic when you ride your ebike. It allows for a more intuitive riding experience and if you want, you can ride hands free. Pedal assist bikes have great built-in cruise controls. Just pedal your bike and the bike goes. Almost all pedal assists system have different levels that you can select with a dashboard that’s mounted on the handlebars.

Here is a video which illustrates how a real torque sensor should work:



So why aren’t torque sensors on every electric  bike?

Torque sensors add considerably to the cost an electric bike. As of this writing, you can plan on a torque sensor adding $200-$300 to the retail cost of an electric bike. The price of adding a simple cadence sensor to a bike is very cheap… figure around $30 retail. That is why the vast majority of commercially available ebikes in the US have cadence senors rather than torque sensors. Torque sensors are more prevalent on higher-end bikes in the European market. There is a big question among ebike manufacturers if American consumers will spend the extra money for a torque sensor.

The US market is different from the European market in these ways:

The limit on European bikes is only 250 watts, but the limit on US bikes is a decent 750 watts. The more power a bike has the less important pedal input is, and thus the less important the torque sensor will be. Most American consumers seem to be drawn to raw performance. A throttle makes an ebike feel more like a motorcycle than a bicycle, and many Americans prefer that. Many ultra performance bikes like the Optibike and the Stealth have never been offered with a pedal assist system.


Advantages of a torque sensor:

For me I almost always prefer a throttle over a torque sensor because most of the time I am lazy. However, if I decide I want exercise, I have found that riding a torque sensored bike is the way to go. A torque sensor makes you work for your power. You can’t cheat the system by shifting into a lower gear and pedaling fast like you would on a cadence sensor system. And lets face it, a twist throttle is the quickest path to laziness there is. A torque sensor makes me work up  a sweat. It really feels like I am riding a bicycle, except I am getting where I am gong faster and not having to walk up any hills.

The second huge advantage for me when I ride a torque sensor is that I get significant amount of range increase when I ride with one…as much as doubled.  This range increase does not come for free, I end up pedaling a hell of a lot more with a torque sensor than I do when I am on a throttle.

Electric bikes are generally super inefficient when accelerating up to speed.  A torque sensor forces you to help the ebike when it needs it the most, when it is accelerating and when climbing.

The other factor of a torque sensor is they make your bike feel like a regular geared bike. You get to utilize your bikes shifter gear train to find just the right gear where you maitain the desired speed for the desired pedal input…same as riding a regular bike. Riding an electric bike equipped with a torque sensor can make you forget you are riding an electric bike at all…once you have that sensation, you know the ebike company has hit it right.


Are torque sensors worth it?

If you prefer riding in Pedal-assist mode, and not using a throttle…then absolutely, the torque sensor is worth the extra cost. You will pay for it quickly by taking less toll on your battery, increase your range, and increase your physical health. The fact is that most cadence sensors feel cheap, and most users if given a choice will definitely choose a throttle over a cadence sensor.

Another issue is a safety consideration with a cadence sensor…imagine you are pedaling hard on a cadence pedal assist system and your chain slips off, which results in you doing some fast rotations on the crankset. This would tell the bike to give you full throttle, and depending on where you are riding this could potentially be a real problem.


How much better is a torque sensor than a cadence sensor?

Torque sensors apply power much smoother than a cadence sensor. On a quality torque sensor, you can forget the bike is electric, the bike just becomes easier to pedal. The harder you push on the pedals, the faster you go like on a regular bike, but with the electric power you just magically go a lot faster. On a bike with a silent hub motor this can feel almost magic, like you suddenly have been blessed with 20-year-old Olympic rider legs.


What are the different types of torque sensors?

Bottom bracket designs

Torque sensor is actually built into the bottom bracket of the bike. The highest quality of this version is called the thun-xcell

Idler wheel on chain torque sensor

torque sensor

A custom torque arm with sensor built in is molded into rear drop out and feels the tension put on the chain. TMM (pictured) is an excellent example of this method.

Strain Guage on rear axle

A strain  gauge on the rear axle, built into the hub motor. This is a Bionx patented system so you will only find this version of torque sensor on Bionx bikes. This is a very nice torque sensor reliable and seamless. With the Bionx software this gives the smoothest blend of electric assist with pedaling that I have felt. Unfortunatley this is s proprietary technology and if you want the best torque sensor on the market you will have to buy a $1800 Bionx Kit, or an  expensive Bionx equipped bike.

Crank sensor

Crank sensors use custom built cranks with the torque  sensor built in.

Spring Guage on Rear Derailleur Hanger


In these photos we see the Stromer rear torque arm with a spring and a sensor which lets the controller know how hard the rider is pedaling.

Here is the sensor mounted on the Stromer built into the rear drop out:

Stromer Torque Sensor

As you can see the hardware is fairly simple for a torque arm, but in this case the frame’s drop outs need to be custom designed.


What if i want to add a torque sensor to my home built bike?


Until recently, if you wanted a torque sensing throttle you would have to purchase one of the few available ebikes with torque sensors (look at bikes below). This year, has released a new version of the Cycle Analyst the V3 (read our report) which allows any home built bike to be transformed into a torque sensing pedelec. The V3 provides the software and dashboard so that you can add one of the hardware modules listed above to your bike and have a torque sensor on your home build. In fact the software provided by the Cycle Analyst seems a lot more sophisticated than the software on the turn key bikes. With the Cycle Analyst, you plug in what percentage of torque assist you want (even if you want over 1000% and the Cycle Analyst will add power accordingly. It is not simple shut on and off like most systems, it applies power incrementally compared to how hard you are pedaling and the amount of assist you have requested.

You can even buy the V3 Cycle Analyst complete with a Thun torque-sensor from the website.  As you can see torque sensors are not cheap. $200 for the Thun, plus the price of the Cycle Analyst ($160).  However by going this way you would have one of the very best dashboards and torque sensors available for an ultra sweet set up.


Thanks to Jeremy of Top Secret EV for providing much of the information for this article. Top Secret Ev specializes in sourcing parts from China (such as torque sensors) for electric bike manufacturers.

List of Commercially Available ebikes I know of (and have ridden) with torque sensors:


Currie Izip Ultra  (read review) Uses a TMM torque sensor built into rear axle.


Stromer (read review) Has a spring gauge torque sensor built into the rear drop out.


Bionx Bikes




Panasonic Drive Bikes (read review)


Bosch Drive System  Bikes (read review):


Eric has been involved in the electric bike industry since 2002 when he started a 6000 square foot brick and mortar Electric Bike store in downtown San Francisco. He is a true believer that small electric vehicles can change the way we operate and the way we think.

  • magic carpet

    Having the torque sensor built into the hubmotor, as opposed to an exposed and seperate attachment makes the BionX the obvious choice, and unlike the Euro spec’d Bosch and Panasonic, BionX also has a thumb throttle.
    When are we going to see a comprehensive review of the BionX conversion kit instead of ebikes that haven’t been released in North America?
    The two most frequent criticisms of BionX are it’s price and it’s incompatibility with other brands of components. Seems to me, if you have a perfected system, you can charge more and don’t need to allow for the compatibility of aftermarket components.

    • ElectricBIke

      Magic Carpet,

      I will try to get my hands on a bionx equipped bike for a test ride and write a review soon. I appreciate your input and will put Bionx high on the list.

      I agree it looks like one of the best options available in terms of kits…..just expensive.

      How many watts is your motor setup?

  • Michael Backus

    It seems like most of these torque sensing setups are ‘reasonably’ powered. My first question is what would happen if you took a big Crystalyte hub and put some serious voltage to it? Would it be possible to go beyond 20 yr old Olympic cyclist to Incredible Hulk? Is that something torque sensing can manage or is the high voltage going to throw the cadence beyond human pedaling range?
    Thanks for creating this fantastic site! I’ve been camping out here for the last couple of weeks absorbing everything. I described your site as “a four year college course in e-bikes” to a friend. You are great for the sport. Thanks!

  • jbond

    In my limited experience of pedelec controlled low power e-bicycles, the power is on-off when pedalling or not. There’s no cadence measurement. I’m fairly sure that the typical low end controller and pedal sensors aren’t varying the max voltage and hence the max speed at all with pedal cadence. But as I say that could just be my bicycle.

    Your statements about torque sensors and range were important. The best way to get extra range out of an electric assist bicycle is not to use the assist! I think this is why Panasonic based mid-drives give long ranges. And I’m sure it is possible to do the same on a hub motor pedelec by using a low assist strategy. For instance setting a max electric speed of 10mph and pedalling enough to keep your speed above this so that you only end up using assist on uphills. Or by using a pulse and glide strategy; Brief bursts of power to push up the average speed but mostly pedal power.

    One issue not mentioned, I think. A Torque Sensor based controller-motor needs to be able to provide instant and on demand power within about a 10th of a pedal stroke. That probably rules out sensorless motors. It may rule out motors with an internal freewheel.

    And I have to agree about pedelec being a good cruise control. That’s exactly how I use it. I typically only use the throttle in heavy town traffic or in nadgery off road where I need fine control over speed and assist. All the rest of the time, I just use the natural bicycle approach of pedalling or freewheeling to control assist or not. It takes no thought and is completely natural. Note however that this is with a medium power top speed of 15mph and a high power top speed of about 20, so bicycle speeds.

    ps. I’ve currently got a 36v-15AHr LiNiCoMn battery with a 350W BPM. My longest journey is just over 50 miles and the battery still powered me up the last hill. That’s done with quite a lot of care to use the power sparingly but also on very mixed ground. A good 10-15 miles of that was off-road bridlepaths.

    • ElectricBIke

      Thanks again for a very insightful comment. We really appreciate your input and knowledge.

  • Goatman

    The “Charger” electric bike sold by Electroportal uses a torque sensor.

    • http://www.electroportal.coom sun-energy

      Thanks for mentioning us, as we’ve been distributing the Charger e-bike now for over 10 years. A strain gauge torque sensor has made this bike a favorite of those wanting an e-bike that retains the feel of a bicycle rather than mo-ped. Because the bike is a ped-elec, the battery range (and life) is far superior to throttled on-demand systems, with the added benefit of a mid drive motor running motor through the rear 7 speed Shimano internal hub. In stop and go city riding the internal gearing is especially sweet since you can downshift at a standstill as well as in motion. Bike tune ups are less frequent due to the ease of adjusting internal gear systems.

      Once our inventory is depleted we still wish to make quality e-bikes to supplement our E4 mid drive motor kit that’s also been very successful. With over 200 wheel sets and other parts we purchased with the Charger bikes, this will ultimately happen. A multi-speed powered pedicab prototype will also become a commercial product as we move towards a world no longer dominated by the car (and oil) industries.

      Attached is a view of the Charger without the side cover.


  • John L.

    I’m considering a Bafung mid-drive kit. Any rumor as to whether Bafung will have a torque-sensor equipped version of their mid-drive motor available any time in the future?

  • Mickey Mouska

    Is there a way to add pedal assist to an e-bike that is sold with throttle only?

  • Mickey Mouska

    I want to add pedal assist to a Prodeco throttle only bike. I want the cadence sensor, not the torque type. Is this possible? Can you show me how to do this?

  • tkj

    I’m surprised not to see the eZee bike and it’s ‘motion sensor disk’ .. a pedelec device at the crank .. a disk populated with magnets.. Not measuring torque but rather mere motion, which satisfies laws in the U.S.A. .. ‘..must be pedaling’ .
    Personally, i’d like ezee ‘s solution to be able to be ‘active’ or ‘inactive’ ..

  • Avinash

    My question is.. does every pedal assists system with a torque sensor need a dashboard on the handle bar with different levels?