A torque sensor is like a throttle that determines how much power to feed the eBike's motor based upon how hard the rider is pedaling.
A cadence sensor is like a throttle operated by your feet. Essentially it measures how fast the rider is pedalling. If the rider climbs a hill and begins to pedal slower, the motor will produce less power where more power is really required.
Selecting either Torque Crank Control or Cadence sensor-based Pedal Assistance all depends on the riding experience you want. Pedal Assist means what it says - In both cases you need to pedal so your eBike knows you are on board so the Motor can add power and motion.
Cadence sensor-based PAS eBikes are generally less costly as you simply select the speed you want to ride at and motor power is added accordingly. When you stop pedalling the motor stops; then when you start pedalling, the Motor starts again at the previously selected speed.
That is, speed is selected as you would use Cruise control on your car. The rider has no control over the acceleration and typically these type of ebikes accelerate most efficiently. However, some have twist-and-go “Limited” throttles fitted to assist you in getting started without pedalling.
Cadence Sensor E-Bikes are typically driven via Rear-Hub Motors, though some have Front Motors where use is mostly on level ground. Some Cadence sensor ebikes also allow you to select eco, touring or power boost modes according to the type of ride you want.
Torque Sensor based eBikes utilise Mid Motors providing a more intuitive and smoother ride as the torque sensor in the Crank Motor determines the motor input you want relative to how hard you are pedalling. The harder you push the pedals the faster you will get to the required speed.
Torque Sensor ebikes allow you to control the acceleration according to the Power Mode you have selected. Also, Mid-Crank Motors are typically more powerful in some cases providing up to 70Nm power.
You work for the power and often feel you are riding a normal bike, but you are getting there faster and not having to battle up those hills. Gear selection becomes more intuitive and you will feel you are riding on a normal bike.
A supplementary benefit of Torque Sensor PAS is that as a result of you having to pedal harder, you get fitter at the same time and also feel more in control. However, just when your legs are getting tired and you want to get home, it could be a slow ride.