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
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
Spring Guage on Rear Derailleur Hanger
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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, Ebikes.ca 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 ebikes.ca 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):
