A recognizable situation: you pedal, but the bike “decides” otherwise
You're driving away from a traffic light and you want to slow down because it's crowded. Yet suddenly the support kicks in hard, or just a little too late. That feeling of “on/off” is the moment for many e-bikers when they wonder: what is my e-bike actually measuring?
The answer is often in the type of sensor that determines how much engine assist you get. In this force sensor vs rotation sensor explanation we explain what happens between your pedaling motion and the engine, and why one approach feels much more natural than the other.
What is the difference between a force sensor and a rotation sensor?
Both systems have the same goal: to tell the engine when and how many support is needed. They just measure something completely different.
- Rotation sensor (cadence sensor): measures whether the pedals are spinning (and sometimes how fast). Support mainly follows the fact that you are pedaling.
- Force sensor (torque sensor): measures how much force you put on the pedals. Support follows your effort.
In practice, this means: a rotation sensor responds to motion, a force sensor on tax. That difference determines how “smooth” and predictable an e-bike feels.
How exactly does a rotation sensor (cadence sensor) work?
A rotation sensor usually consists of a magnetic ring and a sensor that counts pulses. Once the system detects that the cranks are rotating, the motor provides assistance. How fast that support builds and how much it is depends on the support setting and the bike's software.
What do you feel as a rider?
With many cadence systems, the support feels like you're flipping a switch. You put your foot on the pedal, make part of a rotation, and then the motor “picks up.” If you stop turning, the support drops off after a short delay.
Why is there a delay?
The sensor needs a number of pulses to be sure you are pedaling. That may be a fraction of a second, but at low speed or when pedaling very slowly you will notice it. Even when you stop pedaling, the motor may continue for a while, depending on the adjustment.
When does a rotation sensor work fine?
For leisurely tours on flat terrain, this system can be enjoyable, especially if you like to cycle at a constant cadence. It is also relatively technically simple, which makes it attractive to manufacturers.
How does a force sensor (torque sensor) work on an e-bike?
A force sensor measures the torque (torque) you apply to the drivetrain. This can happen in a variety of places, such as in the bottom bracket, in the rear axle, or in conjunction with a gearing/hub system. The gist is the same: the system records how much “pressure” you deliver.
That measurement is continuously read by the controller. Then the software calculates: if the rider provides X power, then we give Y motor power. So you get support that grows with your effort, rather than a fixed push as soon as there is movement.
A simple example on the street
You drive up a bridge and you automatically put a little more force on the pedals. With a force sensor, the engine senses this immediately and provides extra support. At the top of the bridge you pedal more lightly; the support also decreases. You don't have to “play” with assistance settings as much.
Why does a force sensor feel more natural?
“Natural” here means mostly: predictable, proportional and in line with what your body expects. A force sensor aligns with how we ride bikes without a motor.
1) Support is proportional
If you pedal softly, the motor helps softly. If you pedal firmly, the motor helps firmly. That makes the behavior intuitive, even when cornering, at busy intersections or on narrow bike paths.
2) The motor responds to intention, not just movement
When quietly “ticking along” with a cadence sensor, the bike can still support quite a bit, because the system primarily sees: there is rotation. With a force sensor, it matters how many you really do. That feels more like an extension of your legs.
3) Dosing at low speed is easier
In a busy city, sometimes you want to roll through a situation at walking pace. A force sensor makes that easier: little pressure is little help. That reduces the jerky feeling some riders experience with cadence systems.
The main differences at a glance
The table below helps you quickly compare the driving experience and behavior of the two systems.
| Section | Force sensor | Rotation sensor (cadence) |
|---|---|---|
| What is measured? | Power/torque on the pedals | Whether (and sometimes how fast) the pedals turn |
| Feeling during cranking | Gradually, follows your pressure | Frequent noticeable “on/off” transition |
| Dosing at low speed | Mostly very precise | May be jerky or delayed |
| Behavior on slope/bridge | Engine helps more once you push harder | Engine helps as soon as you keep spinning |
| Driving style that fits well | Active cycling, lots of variation in pace | Constant cadence, relaxed touring |
Are there any disadvantages or concerns with a force sensor?
A power sensor has many advantages, but it is not magic. The final driving experience also depends on engine control, software tuning and the rest of the drivetrain.
Note these points
- Tuning and software do a lot: a torque sensor can still feel unsettled if the tuning is aggressive.
- You feel your own effort: because the system tracks your power, “lazy pedaling around” is less effective. For many riders, this is actually pleasant, but it's good to know.
- Maintenance and diagnosis: a more sophisticated measurement system sometimes requires more knowledge in service and adjustment.
What does this mean for an e-fat bike or solid city e-bike?
With heavier, more robust e-bikes (such as e-fat bikes and family cargo bikes), control plays a big role. You have more mass, often wider tires and sometimes extra luggage or a passenger. This is precisely when you want support that can be metered.
A force sensor helps especially in situations where weight and grip require subtle input:
- drive away with load
- tight turns at low speed
- short, bright starts in city traffic
- driveways, bridges and thresholds
Those orienting toward a low-maintenance drivetrain (such as a belt) often also look for a “bike-like” feel in the support.
During a test drive, how do you recognize which system you like?
You don't need to know which sensor is in the bike to feel a difference. A short, focused test ride will quickly bring it out.
Test drive checklist (10 minutes is enough)
- Driving away quietly: turn on very gently. Does the help feel gradual or sudden?
- Driving at walking pace: can you roll slowly without the engine “pushing” you?
- Short sprint: give 2-3 firm kicks. Does the support respond immediately to your force?
- Turn at low speed: does it remain predictable if you half pedal?
- Stop pedaling: does the support drop off immediately, or does it keep pushing?
After that, if you think, “this feels like I'm just cycling harder,” you're often closer to the character of a force sensor.
How does this relate to the official e-bike rules?
Which sensor your e-bike uses does not change the basic rules for a regular pedelec (25 km/h support, rated motor of 250 W). Those frameworks are laid down in European regulations around e-bikes. If you want to check the technical definitions, you can find background at the overview page on electric bicycles on Wikipedia.
Where does this fit within STOER Bikes?
On STOER Bikes, product stories often refer to a power sensor because it helps keep the riding feel closer to “normal cycling.” That aligns with a mature riding experience, especially in urban situations where you often need to anticipate and dose.
A practical next step
When in doubt between two e-bikes that seem similar on paper, put the sensor type at the top of your test ride list. It's one of the few components you feel immediately, every meter.
Want to experience the difference for yourself with your own route (traffic lights, bridges, speed bumps)? Then schedule a quiet test drive via Test ride and pay conscious attention to how the support responds to soft and firm pedaling.