Summary

A torque sensor is a device that measures the force a rider applies to the pedals and converts it into electrical signals to control motor assistance in an e-bike. It enables dynamic, proportional pedal assist that closely mimics natural cycling effort.

Key Facts

Introduced: Early 2000s in high-end e-bikes
Category: Technology / E-Bike Systems
Also known as: Pedal torque sensor, strain gauge torque sensor
Used by / Found on: E-bikes with mid-drive or rear hub motors
Common locations: Bottom bracket, rear dropout, motor spindle, or crank axle
Core function: Measures pedaling force to adjust assist levels
Differentiator: Enables smooth, responsive, human-like pedal assist

Overview

The torque sensor is one of the most important—and often overlooked—components in a high-quality electric bicycle. While batteries and motors tend to get the headlines, it’s the torque sensor that makes an e-bike feel “natural,” “responsive,” or “just right” when riding.

A torque sensor measures how hard the rider is pushing on the pedals, and it sends that information to the motor controller in real time. The motor then responds proportionally: push harder, get more assist; ease off, and the motor dials back its output. This immediate feedback loop allows for a seamless blending of human and electric power, often referred to as proportional or responsive assist.

In contrast to simpler cadence sensors, which only detect that pedaling is happening (not how hard), torque sensors offer a much more intuitive riding experience. They allow for precise control over acceleration, smoother starts from a stop, and better energy efficiency.

For this reason, most mid-drive e-bikes—and many premium hub-drive systems—now use torque sensors as a standard feature. The result isn’t just improved control, but a sense that the bike is actually working with you, not for you.

How It Works

Torque sensors operate by measuring the twisting force, or torque, applied to a rotating object—in this case, the bike’s crankset or bottom bracket spindle. Here’s a breakdown of how this works:

1. Strain Gauges

Most torque sensors use tiny electronic devices called strain gauges. These are bonded to a surface that flexes slightly under load—such as the spindle, crank arm, or a torque tube within the motor assembly. As the rider applies pedal force, the metal deforms microscopically. The strain gauges detect this flex by measuring changes in electrical resistance.

When the material bends, resistance changes.
That resistance is converted into a voltage signal.
The signal is proportional to the amount of torque applied.

This signal is then sent to the bike’s controller, which determines how much motor power to deliver in response.

2. Sampling and Response Rate

Good torque sensors operate at high sampling rates, often reading hundreds or thousands of data points per second. This allows the motor to adjust almost instantly to rider input—resulting in smooth acceleration, fine control on climbs, and seamless transitions in terrain.

Lower-quality sensors or poorly tuned firmware can result in “lag” or over-assistance, which may feel jerky or unpredictable.

3. Location and Integration

Torque sensors can be located in several places:

Bottom bracket (most common): Measures twist on the spindle or crank axle
Rear dropout or chainstay: Measures torque from chain tension
Inside the motor (mid-drive): Integrated within the drive unit
Crank arms or pedal axles: Embedded in portable retrofit kits or some specialty applications

The integration approach varies by manufacturer, but bottom bracket sensors are widely used due to their central location and consistency across drivetrain types.

4. Combined Sensing

Many systems combine torque sensors with cadence and speed sensors. This allows for:

Cadence to determine if the rider is pedaling
Torque to determine how hard they’re pedaling
Speed to modulate assistance within legal limits (e.g. cutting power at 25 km/h or 20 mph)

Together, these create a responsive and legally compliant ride experience.

Importance in E-Bikes and Pedal Assist

Why does torque sensing matter so much for the rider? It shapes the entire experience of how the e-bike feels under your feet. Here’s what torque sensors enable that cadence-only systems can’t:

1. Natural Feel

Torque sensors create assist that feels proportional to effort. This makes climbing feel like riding a lighter bike, not being pulled by an external force. Riders describe the experience as smooth, controlled, and organic.

2. Better Control

On steep climbs or in technical terrain, the rider can modulate assist output simply by easing off the pedals slightly—just like feathering a throttle. This is much harder to achieve with cadence-only systems.

3. Improved Safety

Starts from a standstill are smoother and safer with torque sensors, especially when pulling into traffic or navigating tight spaces. There’s less risk of sudden surging or unwanted acceleration.

4. Battery Efficiency

Because torque sensors deliver assist in proportion to effort, they reduce overuse of motor power—resulting in better battery range on rolling terrain or long rides.

5. Legal Compliance

In many regions (especially Europe), torque sensing is required for “pedal assist” classification, distinguishing Class 1 and Class 3 e-bikes from throttle-based systems.

Notable Implementations

Bosch Performance Line / CX: Uses finely tuned torque sensors integrated into the motor housing. Known for excellent response and climbing control.
Shimano STEPS EP8: Torque sensors combined with advanced firmware enable smart power delivery, especially in Trail mode.
Fazua Ride 60: Lightweight mid-drive with a natural-feeling torque response optimized for road, gravel, and light trail.
Brose Drive S Mag: Offers sensitive torque sensing for quiet, refined assist in urban and trail settings.
Specialized SL 1.1 / 1.2 Motors: Use custom torque sensor tuning for subtle, fitness-style assistance.

Related Terms

References

Bosch eBike Systems Technical Documentation
Shimano STEPS System Overview
Fazua Ride 60 Developer Notes
Brose E-Bike Drive System Specifications
Composites World: Sensor Integration in Lightweight Applications
ElectricBikeReview: Sensor Comparisons and Performance Benchmarks