Using power meter pedals with a spin bike

When using power meter pedals on a spin bike, is there any reason the size of the flywheel would impact the calculated power? I don’t see why it would, but a redditor commenter is suggesting here that the smaller flywheel will result in incorrect power in zwift unless an adjustment is made to the crank arm length entered. I just want to ensure my power is calculated as accurately as possible so would appreciate any thoughts - thank you! (I’m aware of the trainer difficulty controversy (and I am planning on getting a smart trainer/bike) but that is a separate topic :slight_smile: ).

The Assioma pedals measure power at the pedal axle. They contain strain gauges to measure torque and accelerometers to measure cadence. The measured cadence and inputted crank length are used to calculate rotational speed. Power is then calculated from the torque and speed. The wheel size is irrelevant.

I suspect the redditor is confusing power with speed. With a speed sensor on a wheel-on trainer the wheel size does matter; the larger the wheel circumference is the more distance is travelled per revolution of the wheel.

Some people Zwift on a spin bike by attaching a speed sensor to the flywheel. This will give inaccurate power in Zwift and is possibly the source of the confusion.


Thank you! That was my thought as well but I was starting to doubt myself so I really appreciate the response.

I’ve been using Zwift on a spin bike with the Favero Assioma Uno Power Meter pedals. It’s nice to see that there are others out there using the same setup as myself!

As the other commenters mentioned, the size of the flywheel does not matter. Just the length of the crank arm.