Cassette Size?

Hi All, new to Zwift.

Does it matter what ratio my cassette is i have on my trainer?

Not caring about the weight between 105/Ultegra/Dura Ace, but does the ratio of 11/25 - 11/32 make a difference to speed/watt etc?

If it does and there is a place to change it, can you point me to it? I don’t find the interface very easy to navigate.


Hi @James_Grieve

Welcome to the Zwift forum.

the difference between a 11/25 and 11/32 will be that you will have more gears for climbing with the 32.

My suggestion is to get the same gearing as you have on your real bike, that will make riding the trainer similar to your real bike.

If you go for the 11/25 and you feel the mountains in zwift is to hard on your knees then you can always adjust the trainer difficulty down in the zwift settings.

Hi Gerrie.

I understand the theory in cassette ratio’s.

All im asking is if Zwift needs to know what I am riding so the correct information comes and goes to zwift.

I don’t think it will make a difference but im just wondering if there is something in the algorithms that would make a difference.


Your trainer will broadcast the power (in watt) to Zwift and Zwift will use that to calculate speed. You can use any gear you like.

what trainer do you have?

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Elite Direto-X OTS

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Nice, pick any cassette it won’t make a difference to Zwift.


To back up what Gerrie said - the cassette size range doesn’t matter to Zwift. It matters for compatibility with your bike’s drivetrain, in particular what your rear derailleur can handle

We have a guide for selecting a cassette to install on your wheel-off trainer.

It’s best to match the cassette you install on the trainer to the cassette that’s on your rear wheel.

  1. Derailleurs have a limit on the largest rear cog it can handle. Go too big, and shifting on the climbing end of the gears will suffer, or possibly, not shift at all.

  2. If it was installed correctly, the chain on your bike is also cut and sized to the largest rear cog on your wheel. Putting a too-large or too-small cassette will negatively affect your rear shifting because the chain is now too short / long relative to the rear wheel.