Torque sensor vs cadence sensor: why pedal assist feels so different from bike to bike

Ride two electric bikes with identical wattage ratings and you can still come away with completely different impressions. One feels like it reads your effort and matches it instantly. The other feels like it is guessing, a beat behind, surging when you expect a gentle push. The gap usually has nothing to do with motor power. It comes down to how the bike knows you are pedalling in the first place.

That detection method is either a cadence sensor or a torque sensor, and the difference between them explains almost everything about why pedal assist feels the way it does.

What a cadence sensor is actually measuring

A cadence sensor watches your pedals spin. It usually sits near the crank and counts rotations, and once it detects movement, it tells the motor to deliver a preset amount of assistance for whichever mode you have selected. It does not care how hard you are pushing. It only cares that the pedals are turning.

This is a simple, reliable and inexpensive way to trigger assist, which is why it turns up on a lot of entry-level and mid-range electric bikes. The trade-off is responsiveness. Because the system only reacts to rotation rather than effort, there is often a short delay between you starting to pedal and the motor kicking in. Riders describe it as a shove rather than a lift. It can feel abrupt pulling away from a Wellington intersection, then oddly flat on a mellow flat stretch through Hamilton where you only wanted a small amount of help.

What changes when a torque sensor is doing the work

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

The result feels less like the bike is doing something to you and more like the bike is doing something with you. Riders who have used both systems back to back tend to describe torque-based assist as smoother, more intuitive and closer to just having stronger legs than usual, rather than being pushed by an external force. It is also more efficient with battery use, because the motor is not blasting out a fixed amount of assist regardless of what you actually need.

Why mid-drive motors are usually paired with torque sensing

The type of motor matters here too. Hub motors, which sit in the wheel itself, are commonly paired with cadence sensors because they are physically separate from the crank and cannot easily read pedal force. Mid-drive motors, which sit at the crank between the pedals, are positioned exactly where torque can be measured directly. This is one of the reasons mid-drive systems, like the one used in Evolve's Project BMX, tend to deliver that more natural, force-matched feel rather than the on-off surge associated with basic cadence setups.

It is not just about smoothness for its own sake. On a mid-drive bike with a torque sensor, the assist follows the terrain you are actually on. Grind up a steep pinch and the motor senses the extra force you are putting through the pedals and responds accordingly. Roll along flat ground with light pedalling and it holds back rather than overpowering you. That kind of responsiveness is genuinely useful riding through Wellington's hill suburbs or the steeper streets around Dunedin and Queenstown, where the gradient changes constantly and a fixed cadence-triggered assist would either underdeliver on the climbs or overdeliver on the flats.

Where cadence sensing still makes sense

None of this makes cadence sensing a bad technology. For flatter, more consistent riding, such as commuting across Christchurch's grid or cruising along Hamilton's river paths, the difference is far less noticeable. If your riding is mostly steady-state and low-gradient, a well-tuned cadence system can feel perfectly adequate, and the bikes that use it are usually simpler and more affordable as a result.

Where cadence sensing struggles is in stop-start riding and variable terrain. Traffic light starts, tight urban riding through central Auckland, or anywhere you are constantly adjusting effort rather than holding a steady pace, is where the lag becomes obvious. You pedal, wait, then get assist that may already be more than you need for the moment. It is not dangerous, just less refined.

What this means when you are comparing bikes

If you are shopping by wattage alone, you are only getting half the picture. Two bikes rated at the same power output can feel completely different underfoot depending on which sensing method they use. The more useful questions are whether the motor is hub-mounted or mid-drive, and whether the pedal assist is torque based or cadence based, because those two details shape the actual riding experience far more than the number on the spec sheet.

• Cadence sensor: detects pedal rotation, delivers preset assist per mode, simpler and cheaper, slight lag, best suited to flat, steady riding
• Torque sensor: detects pedal force, scales assist in real time, more natural feel, better on variable terrain and hills, typically paired with mid-drive motors

Project BMX uses a mid-drive setup for exactly this reason. With five selectable speed modes and both throttle and pedal assist configurations depending on firmware, the intent is a ride that feels proportionate to your own effort rather than one that simply switches assistance on and off. That is the difference a torque-based, mid-drive system is built to deliver.

If you have only ever ridden a cadence-based hub motor bike, a torque-sensing mid-drive will feel like a genuinely different category of machine, not just a more expensive version of the same thing. The wattage figure on the box was never telling you the whole story.