Torque sensor vs cadence sensor: why pedal assist feels so different

Most people assume pedal assist is pedal assist. You pedal, the motor helps, the bike moves faster with less effort. That assumption falls apart the first time you ride two different e-bikes back to back and one feels like it is reading your mind while the other feels like it is guessing. The difference almost always comes down to what kind of sensor is telling the motor when and how hard to push.

It is a detail that rarely makes it onto a spec sheet in plain language, yet it shapes almost everything about how a bike feels underfoot. Understanding it properly changes how you shop, and it explains a lot of the frustration people report after buying a bike based on battery size or motor wattage alone.

What a cadence sensor is actually measuring

A cadence sensor watches how fast the pedals are spinning, nothing more. It sits near the crank and counts rotations. Once it detects that your legs are turning over, it tells the motor to deliver a preset amount of power, usually in steps tied to whichever assist level you have selected.

The catch is that cadence has nothing to do with effort. You can spin the pedals fast with almost no resistance, or turn them slowly while grinding up a steep pinch near the Gold Coast hinterland with real force. A cadence sensor cannot tell those two situations apart. It only knows the pedals are moving, so it applies the same assist regardless of how hard you are actually working.

This is why cadence-based systems often feel like they arrive a beat late and then deliver more push than the moment calls for. There is a small delay while the sensor registers movement, then a surge as the preset power kicks in. On flat, steady riding it is barely noticeable. On stop-start city riding, at lights through the Brisbane CBD or along a busy Sydney bike path, that lag becomes obvious every single time you pull away from a stop.

What a torque sensor is actually measuring

A torque sensor measures force, not motion. It sits in the bottom bracket or crank area and reads how hard you are pressing on the pedals in real time, then scales the motor's output to match. Push harder and the motor gives more. Ease off and it eases off with you.

The result feels less like a motor switching on and more like your own legs suddenly got stronger. There is no waiting for the system to notice you are pedalling, because it is responding to pressure rather than rotation. Climbing out of the saddle on a steep section, the assist ramps up smoothly with your effort instead of arriving as a single burst partway through the climb.

This is the sensor type that tends to show up on bikes built around mid-drive motors, where the motor sits at the crank and drives the chain directly rather than spinning a wheel hub. A mid-drive system paired with torque sensing is designed around the idea that power should feel like an extension of your own pedalling, not a separate force bolted onto the bike. It is a big part of why mid-drive bikes, including the setup used on Project BMX, feel more like a bike and less like a bike being pushed from behind.

Why the difference matters more in hilly, stop-start riding

Flat, uninterrupted riding hides the gap between the two systems reasonably well. Once you introduce gradient changes, traffic, or tight urban riding, the difference becomes obvious fast.

Melbourne's inner north, with its short punchy rises and constant intersections, is a good example of terrain that exposes a cadence sensor's weaknesses. You are constantly starting, stopping, and adjusting effort, and a system that only reacts to pedal speed struggles to keep pace with those changes. A torque-based system, reading actual force, adjusts itself moment to moment without you having to think about it.

Perth's flatter, more consistent riding conditions are more forgiving. On long, steady stretches along the river or through wide suburban streets, a cadence sensor's delay matters less because there is less variation in effort to track in the first place. This is worth knowing if you are trying to work out which spec actually matters for the way you ride, rather than chasing every number on a page.

Battery and motor size do not fix a bad sensor

It is tempting to assume that a bigger battery or a more powerful motor solves any pedal assist complaint. It does not. A 750W motor with cadence sensing will still deliver power in the same slightly delayed, slightly abrupt way as a smaller motor using the same sensor type. The wattage changes how much force is available, not how naturally that force is delivered.

This is worth remembering when comparing bikes on paper. Two bikes with near-identical battery capacity and motor output can feel completely different to ride, purely because one reads torque and the other reads cadence. If a spec sheet does not mention which sensor type is used, it is worth asking directly, because it tells you more about the actual riding experience than most of the other numbers combined.

What this means if you are new to pedal assist

If you have never ridden an e-bike before, a torque-sensing, mid-drive setup is generally the easier system to trust. Because it responds to your effort rather than a fixed assist level, it tends to feel more predictable in mixed conditions, whether that is weaving through foot traffic on the Gold Coast beachfront or climbing away from a set of lights in central Sydney.

Cadence-based systems are not necessarily worse, and they are common on more affordable bikes for good reason. They are simpler, cheaper to produce, and perfectly adequate for flat commuting or recreational riding where sudden changes in gradient or effort are rare. The honest answer is that neither system is universally better. They are built for different kinds of riding, and the right one depends on the terrain you will actually cover most often.

If you are shopping for an e-bike and pedal assist quality matters to you, do not let battery size or top speed dominate the decision. Ask how the assist is measured. A torque sensor on a mid-drive motor, like the setup behind Project BMX, is going to feel more natural under real effort, especially anywhere with hills or constant stopping and starting. A cadence sensor will get you there too, just with a slightly different rhythm underfoot. Once you have felt the difference between the two, you will understand why the sensor matters more than almost any other number on the spec sheet.