A torque sensor is a type of throttle that determines how much juice to feed the motor based on how hard the rider is pedaling. This is different from a cadence sensor which measures simply how fast you are pedaling. Cheap cadence sensors are what can be found on most pedal assist system (PAS) bikes on the market today. When done right, a torque sensor can make you feel bionic when you ride your ebike. It allows for a more intuitive riding experience and if you want, you can ride hands free. The price of a simple cadence sensor is very cheap compared to the cost of a torque sensor. That is why the vast majority of commercially available ebikes have cadence sensors rather than torque sensors. Torque sensors are more prevalent on higher-end bikes in the European market.
Advantages of a torque sensor: if you decide to make exercise and have a long range, riding a torque sensored bike is the way to go. A torque sensor makes you work for your power. You can’t cheat the system by shifting into a lower gear and pedaling fast like you would do on a cadence sensored system. A twist throttle is the quickest path to laziness there is. With a torque sensor you will really feel like you are riding a bicycle, but you will go faster and longer distances, not having to walk up any hills. You will get significant amount of range increase with torque sensor compared with cadence as much as doubled. Electric bikes are generally super inefficient when accelerating up to speed. A torque sensor forces you to help the ebike when it needs it the most, when it is accelerating and when climbing. The torque sensor makes your bike feel like a regular geared bike. You get to utilize your bikes shifter gear train to find just the right gear where you maitain the desired speed for the desired pedal input, same as riding a regular bike. Riding an electric bike equipped with a torque sensor can make you forget you are riding an electric bike at all once you have that sensation, you know the ebike company has hit it right.