Bonjour,
Mon fils possède un Zwift Hub (classique) avec une cassette SunRace 11 vitesses.
Tout fonctionne correctement pour lui.
Comme il ne l’utilise plus vraiment, j’aimerais l’utiliser avec mon vélo pourvu d’une cassette Shimano Claris 8 vitesses.
Je n’arrive pas à la monter sur le Zwift Hub car le diamètre de ma cassette n’est pas identique à la sienne.
Voir photos.
Que dois-je faire?
Acheter un adaptateur? Si oui lequel?
Merci d’avance!
Hi, I hope English is okay.
You actually took off both the cassette and the freehub from the Zwift Hub. The latter can stay on the trainer. Then use a locking tool and a chainwhip to take off the Sunrace cassette from the freehub.
Your 8-speed cassette should now slide onto the freehub - orientation is helped because one of the splines on the freehub is wider than the others. As the freehub has become a bit longer when 11-speed was introduced, you‘ll need an 0,85mm spacer to fit your cassette correctly. You should get this at your local bike dealer or online. Put the spacer on the freehub first, then the cassette. Then put on the lockring - make sure all sprockets of the cassette sit properly and are equally spaced, then add the lockring - which has threads which are fairly fine, so thread on with some care. Once on, tighten down the lockring ‚properly‘.
If in doubt, your local bike dealer will be able to help with the installation.
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Should be 1.85mm 
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Isn‘t 1,85mm the size of spacer needed to put a 10-speed cassette on a 11-speed HG freehub? I thought because 10-speed cassettes were 1mm narrower than 8-/9-speed cassettes that in this case 0,85mm should be the right size.
This is all without much hands-on experience, just from reading the Sheldon Brown pages. I only entered the Shimano world with 10-speed (was on Campa 8-speed before that).
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Should be the same instructions as for a Wahoo trainer:
The spacer should have come with the trainer:
Some 10 speed cassettes come with an additional 1mm spacer, but not all of them do and using it may or may not be strictly necessary. This looks like a pretty good answer about that:
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Hello Magnus, hello Paul,
Thank you so much. You are both completely right (and I was stupid not to have spotted this by myself). The information you gave me is so complete, you did an amazing job for me. I first asked to the zwift support team (by email) but I’m pretty sure that their answer was generated by AI because it was not efficient at all, they just adviced me to buy their zwift cog 
Once more, many many thanks for your wonderful and efficient help!
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