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.

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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.

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Have my Assioma uno coming shortly and using a spin bike. How are you finding it?

Hi Patrick. I’m considering the Favero uno pedal to use on my spin bike. I currently have wahoo speed & cadence sensors attached to it but would like to get rid of my zp on Zwift power so I can race.

Just wondering if you’re happy with the setup please?

Do you use anything else (sensors etc) on the bike to work with the Favero Uno pedal?

Thanks

I have been using a Tacx Neo 2T for over a year and love it. I just installed Assioma Favero Uno pedals on my spin bike and tested several crankarm lengths with the AF (lol) app. Even at the accurate measurement of 184.2 for the crank, my power numbers are higher on sprints than on my controllable trainer.

At the lower end I’d say the power is about the same as on the Tacx, however, while it takes considerable effort for me to get into the 400’s and over 500 briefly on the Tacx, I was easily able to maintain 480w on the spin bike with AF.

Has anyone else experienced anything similar or have a suggestion?

Check in the Assioma app that Double the Power is OFF.

Here is an old post

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2 years later, how are you getting on with this setup? I’m considering the Uno’s for my spin bike. Any feedback appreciated!

I have a Bowflex C6 spin bike and Assioma Uno pedals work great. Make sure double power is off for pedals and unplug the bike too. Have made some mods to the bike to mimic my bike as closely as I can. Quite happy with this set up.

What mods have you made out of interest? Do you find the power is accurate on your spin bike?

I installed the Assioma Uno’s on my spin bike recently but as Zwift is my intro into anything remotely cycling related it’s difficult to tell if my power is accurate.

The power figures seem to jump around quite a bit, usually ~30 watts.

The Assiomas is very accurate power meters.

Set your Power display to 3 second average.

Also when last did you service the spin bike pads?

Thanks for the response Gerrie. My settings are correct and the pad is new and lubed etc… There’s a good chance that I’m a very average Zwifter but I have no data to work with as I only have this bike and the Uno’s.

My FTP is 160W and I struggle to maintain over 2 watts per kg. I’m 90kg,192cm, and very active so I might be wrongly assuming that my power output should be higher. I’m happy with whatever the result is, I just want some confirmation that it’s correct!

With regards to the variable power, I suspect this is a byproduct of using a spin bike or a rubbish pedal technique.