Electric Bikes: What are the Differences Between Rotation and Torque Sensors


Easy E-Biking - Engwe Engine X e-bike motor, helping to make electric biking practical and fun
Photo credit ENGWE e-bikes

The purpose of an electrically assisted bicycle is to reduce the effect of your effort, either to avoid sweating when you arrive at the office or to accompany the athlete on their journey. To do this, there are two leading technologies that you need to know before buying an e-bike: the torque sensor and the rotation sensor.

As their name suggests, e-bikes, or electrically assisted bicycles, assist you in pedaling to make riding rather effortless. But this assistance varies according to the technology used. The differences are felt in the purchase price and the pedaling sensation. Therefore, we have decided to explain effectively how these differences manifest themselves.

Read also: How to use gears on an electric bike (mechanic and electric)? – in this article. And, How to switch electric assistance levels on an e-bike? – in this article.

Here is what you need to know about electrically assisted bike sensors.

E-bike is a sensor

A sensor is a component or a set of electronic components used to measure a phenomenon. As its name suggests, the electrically assisted bicycle assists you in your effort. To do this, it needs to know whether you are struggling or whether you do not need help.

The engine is thus linked to an effort sensor system.

There are two schools of thought: the rotation sensor, which measures the number of revolutions made by the pedals, and the force (or torque) sensor, which measures the effort applied to the pedals.

A third school exists: it uses both technologies to offer the best assistance.

Rotation sensor: cheaper but less natural

The rotation sensor is a much more affordable technology than the torque sensor. You can find it on entry-level e-bikes. It detects the rotation of the crankset. The detector indicates the number of cycles per minute. From this, the bike manufacturer will choose the interpretation made by the system and adapt the engine support accordingly.

For example, the system may be based on two pieces of data:

  • Crankset not turning: no assistance is provided;
  • The pedals are turning: maximum aid is provided.

In this case, maneuvering in traffic is not easy. So you usually stop and then restart your pedaling to manage your speed as best as possible in the middle of other cyclists.

Easy E-Biking - e-bike middle Bosch motor, helping to make electric biking practical and fun

Also, be aware that there is usually a waiting time at the first pedal stroke before you receive electric assistance: it takes at least one turn of the pedals for the sensor to realize that help is needed. Therefore, it is essential in this case that your e-bike is balanced correctly not to wobble when you start.

The system can interpret the message in two other ways to provide progressive assistance adapted to the cyclist’s pace:

  • The crankset turns quickly, so the cyclist is not struggling much, which means that the rider most likely does not need help;
  • The crankset turns quickly, the cyclist is working, and some electric assistance could be helpful.

The rotation sensor offers unnatural assistance. The system usually considers the following: the fewer the crankset turns, the less service the cyclist will need. That is the case with the VanMoof S3, for example. On flat routes, such as in the Netherlands, it is beneficial and even allows maximum assistance when minimal effort.

Read also: Can e-bikes help go up steep hills? – in this article. Or how to switch electric assistance levels on an e-bike? – in this article.

That is one of the reasons why VanMoof adopted this system on the S3. On the other hand, at the bottom of a hill to climb, your rotations will be slow. The system will not consider that you need help when you do. As a result, this becomes a pain in the back.

Torque sensor: be one with your e-bike

The pressure sensor, also known as the torque or power sensor, has nothing to do with beer, but it’s still cool. It works based on the rotational force (the moment) exerted on the pedal. That tells whether you are struggling or do not need assistance. But, of course, the harder you push, the more the engine will assist you.

The assistance is therefore sent proportionally according to the intensity you put into your pedaling. For example, this type of sensor can be found in the Cowboy 4 ST, the Moustache Lundi 27.3, the Weech, or the Harley-Davidson Serial 1 MOSH/CTY.

It is the technology to adopt for extreme activities, technical routes, and, more generally, if you are looking for natural, low-intrusive assistance. The assistance acts as if your muscles have woken up in your legs. The system also puts a smile on your face when you first try an electrically assisted bike.

Easy E-Biking - Vanmoof e-bike, helping to make electric biking practical and fun
Photo credit Vanmoof bikes

You can find it on most mid-range and high-end models.

The system consists of a kind of plate with a mechanical tilting system. This system tilts when the effort on the pedal is high and repositions itself when you lift your foot. Such a system can deliver 104 pulses per pedal revolution and 1000 torque variations per second.

The main disadvantage is the adjustment, which must be perfect: if it is too tight, the system will consider that you are in a permanent effort; too loose, it will assume that you do not need help (since it will not measure a sufficiently remarkable variation). To overcome this adjustment problem, engine manufacturers such as Bosch or Shimano have integrated this force sensor directly into the crankset.

Read also: How much elevation / altitude can electric bikes climb? – in this article. And, Can electric bikes go up steep hills? – in this article.

Note that the torque sensor is never alone. It can be associated with a rotation sensor for speed indications (for example, it could switch off electric assistance, at, say 25 km/h, which is the European regulation). The rotation sensor is also used to inform the engine, and the onboard computer connected to it about the distance traveled.

Which one is better – rotation or torque sensor?

Logically, the torque sensor alone – or in combination with the rotation sensor – provides much better assistance than the rotation sensor alone. It offers a much more natural and pleasant ride. When properly calibrated, it allows you to become one whole with your e-bike.

The advantage of the rotation sensor is its much lower price, which makes it possible to develop electrically assisted bikes at a lower cost for leisure use or without having to deal with unevenness. On one hand, the weight gain is negligible. On the other hand, the riding sensation is much less natural.

The rotation sensor is generally found on entry-level bikes. However, on bikes costing an average of 2,000 dollars or euros, check that a torque sensor is included.

Read also: How to select the best e-bike for your needs? Making your educated e-bike selection choice – in this article, this article, and this article. And, how much does a good e-bike cost? Comprehensive e-bike pricing guide (with 46 examples) – in this article.

Riding, testing, and writing about e-bikes since 2017.

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