Torque sensors explained

You pull away from a stop and the help feels slow. Or it feels spot on. Some bikes read how fast you pedal. Others read how hard you push. A torque sensor reads the second one.

What torque means

Torque is twisting force. When you push down on a pedal, you twist the crank around the bottom bracket. The bigger the push, the bigger the twist. Gazelle, a bike maker, says torque sensors measure how hard you're pedaling.¹

How it matches the help to your effort

The idea is simple. Gazelle writes that the more force you apply to the pedals, the more power the motor delivers.¹ Gazelle also lists, as a plus of this style, that power output adjusts dynamically to your effort.¹

A controller does the matching. One reference says an electronic controller is needed to modulate the motor according to your pedaling.² It adds that EU-defined pedelecs use this approach. The aim is smooth acceleration and cutting motor power when required.²

How the sensor measures force

Makers use a few designs. One reference says force can be measured by torque sensors near the crankset, or with strain gauges on the axles of hub motors.² A strain gauge is a small part whose electrical reading changes when metal flexes a tiny amount. Push harder and the metal flexes more.

Where the sensor sits changes what it can read. The where the sensor sits page goes through the options.

How old the idea is

It's not new. One reference says torque sensors and power controls were developed during the late 1990s.³ The pedelec reference adds that Yamaha's PAS bicycle, first shown in late 1993, used torque and speed sensors.²

Troubleshooting a slow start

A torque sensor reacts to force, so a start with very little force can bring very little help. Here's what Gazelle says about it, and what to try.

• You have to push to get help. Gazelle says this style can help the rider get going faster, since the first pedal stroke is often the hardest. It also says the rider must exert quite a bit of effort to trigger the electric assist.¹
• Shifting down seems to make it worse. Gazelle calls this counterintuitive: as you shift down when stopping or climbing, the pedals feel lighter, so there's less force to read.¹
• It tires you on long rides. Gazelle lists this under things to keep in mind, saying this style requires more consistent effort to keep higher assistance.¹
• Nothing changes after all that. Check the assist level on your display, then your manual's error codes. A dealer should handle any sensor repair, and the manual for your own model has the steps that apply to it.

What a torque sensor doesn't do

It doesn't pick your assist level, and it doesn't set the speed limit. Those come from your settings and the law in your area. The pages on levels and classes cover those.

For a side-by-side look at both types, read torque or cadence.