Extra washer in box

I just unboxed my new trainer and there was an extra washer in there…about 1 1/2" in diameter, looks similar to a headset washer. Any ideas what it’s for?

Typically goes behind your cassette if you’re not running 11spd, but you need to check first.

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Looks like it could be a cassette spacer. If the trainer came with the correct cassette already installed, then you probably don’t need that spacer. Trainers support cassettes with various different numbers of cogs, some of which will require a spacer and others not.

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What trainer, cassette and groupset speed you using?

Sorry, it’s the latest Zwift trainer. Came with 10 sp cassette installed. Shimano 105 on the bike

Hmm, does the cassette installed on the trainer have a spacer under it?

Hmm good question. Guess I’ll have to remove it to check. I bought it preinstalled so I wouldn’t have to do this

If the cassette isn’t visibly loose when you try to move it sideways, there definitely is one in there already. They probably have a pile of them where they install the cassettes and don’t want to touch the OEM accessories.

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Ok thanks. It seems fine, I gave it a 10 minute test ride and worked ok. Need to fine tune my derailleur though. I’ll double check tomorrow. Happy New Year everyone.

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