E-Bikes that feature pedal assistance, provide power when the pedals are turning. How does the e-bike know that the pedals are turning? Well there are 2 common methods that are used – either a torque sensor or the incorrectly named, speed sensor.
A torque sensor is a highly sensitive device called a strain gauge that is usually found in the bottom bracket, which measures how much power you are putting into the pedals. It is highly calibrated and measures the input many times per second. This input can then be accurately mirrored with the appropriate amount of motor assistance.
An e-bike with a torque sensor consequently gives a very natural feeling, as it constantly adapts the motor power depending on the riders input. This is ideal for technical mountain biking where you don’t want any excess or unwanted power whilst on navigating rocks and roots. This constant variance in power output means that there is less power assistance provided overall, and hence you tend to get more range with a torque sensor. The downside is that well, it feels like a lot more hard work! Want more power, well you’ll need to put more power in!
Firstly it’s not a speed sensor, it’s actually a cadence sensor, and it measures how fast the pedals are moving, it does not register however how much power is going through them. It is a simpler device, the power assistance is varied according to how fast the pedals are turning.
This gives a greater feeling of assistance, and if you are getting tired, you can simply shift down a few gears and let the motor do most of the work. It’s more of what you would expect from an e-bike, it does however tend to use more battery power, as there is less input required from the rider.
Just remember that there are also differences between brands of torque sensor and speed sensors too. Some torque sensors are quite laggy, and conversely some speed sensors have higher sampling rate which improves responsiveness.
Comparatively a torque sensor is a much more complicated device, and adds about $200 at retail, and therefore often sold as being “better” as it is more expensive. However this is not always the case, as many riders prefer speed sensors. As always it is best to try them out and determine your preference.