Why does it ask for my wheel circumference on a direct drive trainer?

I might have a bigger tire or a smaller tire in real life but that shouldn’t matter on the trainer (and I’m worried it could give inaccurate speed figures in Zwift).

Example - gravel bike with a 700x44 tire vs. road bike with a 700x25 tire - at a given wheel (flywheel) speed, the bike with the bigger tire would be going faster (larger circumference). That shouldn’t be relevant in Zwift.

Anyone have a thought on this?

Does Zwift actually use any of the settings from the Wahoo app?

(using a Kickr Core)

This may help you: How Does Zwift Determine My Speed?

And Zwift will only ask you for wheel size if you are using a speed sensor. If you are using a power meter or smart trainer Zwift will use power and not wheel speed to determine in game speed.

If you have aDirect Drive trainer make sure you are connecting it as a power source and controllable trainer.

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Do you pair your trainer as a power source and controllable.

I don’t think Zwift use the settings from the app.


As Gerrie and Paul said, it shouldn’t be asking for a wheel size with the Core paired correctly. I use one too and don’t need to specify this.


Sorry - I wasn’t clear. The Wahoo app is asking for this (not Zwift itself). Sounds like the Wahoo settings don’t actually matter - Zwift is getting data from the trainer directly and not flowing it through the Wahoo app?

That is correct, Zwift is getting the power and cadence from the trainer directly.

Your trainer is asking for this so it can calibrate itself.
My Elite Drivo does the same.
It’s a one time entry… But the figure on an Elite trainer gas to be altered afterwards by a set number which I can’t recall now.
This when setup on your trainer will give the correct data to Zwift.

Ride on