You may know the feeling: you put in one half revolution and the motor is already firing. In heavy city traffic this can seem pleasant, but on longer rides it quickly feels as if the bike is setting your pace. Especially on e-fat bikes, where grip and stability are great, such an “on/off” feeling is especially noticeable in your knees, hips and cadence.
The crux of that difference is often not in the battery or engine power, but in the sensor that determines when and how many support you get. If you search on what is a power sensor on an e-bike, you are actually looking for one thing: why does one e-bike feel like a bicycle and another like a moped with pedals?
What is a power sensor on an e-bike?
A force sensor (also called torque sensor called) measures how much force you put on the pedals. The motor then supports in proportion to your input. If you pedal softly, the support is subtle; if you turn on, you get noticeably more help.
This makes the support “fluid”: you don't feel a harsh transition between no help and help. The system reads your intention through pedal pressure, not just movement.
Where is such a force sensor located?
The exact location varies from e-bike to e-bike. Many systems measure torque in or around the bottom bracket, others in the drivetrain or through a combination of measurement points. For you, the rider, the outcome is more important than the location: the motor responds to pressure, not just going around.
Rotation sensor versus force sensor: the difference in one ride
A rotation sensor (often cadence sensor called) measures whether the pedals are turning. As soon as the system detects “rotation,” the motor provides support according to the selected position. How hard you pedal is less decisive; it is mainly: is it spinning or not spinning?
This explains why some e-bikes provide strong support even with very light pedaling. And why you sometimes have to “keep pedaling” for a while before the motor cuts back.
Practical comparison
This table helps to translate the driving experience to concrete situations. It is not about right or wrong, but what suits your use.
| Situation | Rotation sensor (cadence) | Force sensor (torque) |
|---|---|---|
| Accelerating at a traffic light | Support often comes in as soon as your pedals move; can give “bite” | Support builds as you push harder; feels controlled |
| Cycling quietly among pedestrians | Chance of too much help at low speed, depending on adjustment | You can pedal very lightly and still ride stably slowly |
| Cornering out of acceleration | Support may deploy just too early or too late | You “dose” with your legs; engine follows your power |
| Up ramp or bridge | Often constant push; you sometimes go faster than your cadence likes | More pressure = more help; you keep your own rhythm more easily |
| Driving with luggage or child(ren) | May be okay, but feels less ‘human’ under varying loads | Adjusts instantly to additional weight as you automatically push harder |
Why a force sensor feels more natural
Cycling is all about micro-adjustments: pushing a little to get out of a corner, pedaling a little slower on a narrow bike path, applying a little power on a bridge. With a force sensor, that game remains intact, because your pedal pressure remains the “throttle.”.
Many riders describe it as, “like I suddenly have stronger legs.” Not because you go faster without effort, but because the bike amplifies your effort.
Signals your body recognizes
- Instant feedback: if you push harder, the support responds immediately.
- Less surprise: no sudden spike when just getting a pedal around.
- Constant line: easier to keep exactly the same speed in crowds.
What does this mean for your knees?
Knee pain on the bike rarely arises from a single cause. It is often a combination of saddle height, pedaling frequency, acceleration, load and how “jerky” you deliver power. A power sensor changes especially the latter: the bike supports gradually, making you less likely to get into weird pedaling moments.
1) Fewer “push and pull” moments
With some rotation sensors, you unconsciously start compensating: you don't pedal for a while, or you just pedal against the support. This can lead to short, high spikes in force on your knees, especially when pulling up and at low cadence.
With a force sensor, that tendency is less, because you don't have to “fiddle” to get the motor on or off. You pedal like you're used to, only with extra help.
2) Cadence remains your choice
A pleasant cadence (pedaling frequency) helps many cyclists put more gentle pressure on knees. If the support kicks in too strongly at low speed, you sometimes start turning slower than feels right because the bike is pushing forward anyway. A power sensor makes it easier to stay in a round, smooth rhythm.
3) Better dosing at low speed
Especially in places where you have to brake and accelerate often (intersections, traffic circles, school streets), abrupt support can be annoying. Controlled acceleration often also means: less torsion on your knees in the first few meters.
Please note that if you have existing knee problems, then bikefit and medical check remain leading. This explanation is about riding feel and loading patterns, not treatment.
Cadence explained: why some e-bikes “hijack your pace”
Cadence is the number of revolutions per minute. On a regular bike, your cadence is a direct reflection of speed, resistance and fitness. On e-bikes, sensor logic can change that relationship.
With a rotation sensor, support can be relatively unrelated to your power. This can cause you to end up in a cadence that doesn't suit you: either too slow (heavy pushing) or too fast (pedaling in a vacuum) if you don't choose the gear properly.
This is how you notice it in practice
- You ride fast, but it feels like you have little real pressure on the pedals.
- You shift (if you shift) not because you have to, but because otherwise the engine responds “weirdly.”.
- You keep your legs still in turns or crowds to prevent the bike from jumping forward.
A power sensor makes it easier to ride your own cadence because the support is not just “on,” but moves with your pressure and rhythm.
What does this mean for e-fat bikes and heavy use?
E-fat bikes are often chosen for stability, grip and comfort. Consider streetcar rails, bad road surfaces, speed bumps and riding with a heavy bag. In such conditions, the load is constantly changing.
A force sensor can be nice there because it instantly reacts to extra resistance. You need to think less about the support; your legs do what they always do and the motor replenishes.
Also in the background are technical choices that affect the driving experience, such as drive train and maintenance. If you're curious about how a belt behaves while driving, read also how a belt drive affects the pedaling experience on a fatbike.
What do you look for during a test drive when looking for “natural pedaling”?
A spec list doesn't tell everything. During a test run, include a few situations where sensors give themselves away.
Checklist for 10 minutes of testing
- Pull up: does it feel like a gradual push or a switch?
- Slow driving: can you remain stable at low speed without unexpected acceleration?
- Varying Cadence: consciously try going around faster and slower; does the support stay logical?
- Turn off: turn on very lightly and then firmly; does the bike respond as you expect?
- Stop pedaling: does the engine build down immediately, or does it still push through?
A useful background source on how pedelecs and e-bike support are defined in Europe (and why “coasting” is a basic principle) can be found at Wikipedia on pedelecs.
How STOER looks at “natural pedaling”
At STOER, the riding experience cannot be separated from safety and control. In practice, that means: support that is predictable, so that in heavy traffic you don't have to guess what the bike is going to do.
Our story about the creation of STOER echoes this point: the idea that you really need to pedal along and that the bicycle is not meant to be a souped-up gadget.
Frequently asked questions about force sensors
Is a force sensor always “better”?
No. A rotation sensor may be fine for short, flat rides where your main concern is convenience. A power sensor is often chosen by people who value control, bike feel and a natural cadence.
Does a force sensor feel heavier?
It can feel more “active” because your input counts. You get support as soon as you apply pressure, but you can't be completely passive. Many riders actually like that because it feels more like real cycling.
Can I prevent knee pain with a force sensor?
A sensor is not a guarantee. However, smoother support can help avoid jerky loads. Saddle height, pedaling technique and appropriate resistance remain crucial.
Next step without a buying guide
When in doubt between “on/off” assistance and a bike that follows your power, one thing helps the most: ride it yourself. Schedule a test ride and pay conscious attention to acceleration, slow riding and cadence, or get in touch if you want to spar about which riding style best suits your commute or family rides.
Practical: via the page Test ride you can choose a test drive time that fits your schedule.