How Do Cycling Power Meters Work?

How do power meters work: power2max power meter assembly

I’ve always been curious about how things work. And if the thing was cycling-related, I had to find the answers. This is doubly true for cycling power meters.

That’s why I reached to power2max and 4iiii to help me explain the technical details. So, we joined forces and wrote this easy-to-understand explanation of how cycling power meters work.

Are you ready to learn more?

Let’s dive in.

Big thanks to power2max and 4iiii for helping me with the technical explanations.

What Are Cycling Power Meters?

Cycling power meters are devices that measure (estimate is a more precise word, see the technical explanation below) a rider’s power output. They then transfer it to a cycling computer or other devices with ANT+ or BLE connectivity.

Their main advantages include objective and instantaneous data cyclists can use for improving their training effectiveness. You can read this article on Why use a power meter and to learn more about their benefits.


How Do Cycling Power Meters Work?

Surprisingly, no power meter measures power. To understand how power meters work, you must understand what power is. This requires some knowledge in physics:

P(ower) is W(ork) divided by t(ime).
P=W/t

And:

W(ork) is F(orce) times d(instance).
W=F×d

A power meter can measure the Force (torque) by using strain gauges and time and distance by using cadence, which can be measured with an accelerometer or, in some cases, an external magnet.

What is a strain gauge?
Strain gauges measure strain on an object. This can be a crank spider, crank arm, or the axle of a pedal. A strain gauge is a very small and sensitive foil with a defined electric resistance. If the object is deformed (when force is applied during a pedal stroke), the electric resistance changes by a very, very small amount. This change is registered, and calculations are made to know how much force was applied. In the case of a rotating object like a crankset, this force is called torque.

power2max power meter being tested
power2max power meter testing | Source: power2max

The vast majority of cycling power meters are direct force power meters.

They use strain gauges to measure torque. These power meters include all power meter types except handlebar power meters.

However, there are also opposing force power meters (like handlebar power meters). Instead of strain gauges, they use other sensors (like an accelerometer, speed sensor, wind pressure sensor, elevation sensor) to calculate power.

What Is Power Averaging, How It Works, and Why It Is Important?

Power averaging is the process of averaging power readings. It is required because during rotation the force on the crank fluctuates wildly.

The power meter will take a reading of the instantaneous power 4 times a second and average those readings.

Illustration of variable power over time
Illustration of variable power over time

For example, on the downstroke for a 1/4 of a second, your power could be 600 watts, the next 1/4 second on the upstroke could be 100 watts. That would be reported as 350 watts at 120rpm.

The 1/4 second measurements on their own don’t provide valuable data, but when we average the readings the results give the rider something meaningful to work with.


Cycling Power Meters FAQ


Summary

Most power meters on the market use strain gauges for measuring torque and accelerometers for measuring cadence. Then, they calculate the power by multiplying these two units. These are called direct force power meters and include pedal, crank arm, spider, and other commonly known power meter types.

There are also opposing force power meters. They include handlebar power meters that use different sensors for measuring and calculating your power based on your speed, acceleration, wind pressure, temperature, etc. In other words, they don’t measure the force you put into every pedal stroke, but the opposing forces.

If you have any further questions regarding power meters, feel free to add a comment below.

Preview picture source: power2max

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