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I am farily new to cycling and roadbikes in general. I have bought a ( last years model ) roadbike with an 8 speed casette in the back. I also bought an indoor trainer ( 2nd hand ) and got a spare wheel with special training tyre on it. However, the casette on the spare wheel is an 11 speed. I have tried to fit that wheel on my bike, but the 11 speed does not ride well on my 8 speed bike. I took it off to prevent any possible damage to the bike and or wheels.

Is it possible for me to simply take out 3 cogs from my 11 speed wheel, and thus make it an 8 speed? If so, how do I determine which ones to take out? Or would it be better if I 'downgrade' my spare wheel to an 8 speed? Or upgrade my bike to an 11 speed ( but I think this will be to expensive for me right now )?

Keep in mind the bike is new, so the 8 speed casette is not even worn out. The 11 speed wheel is used, but looks in very good shape. Also my budget is very limited. Thanks for any helpful tips

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The spacing/pitch between the individual cogs of the 8 and 11 speed cassettes are different so if you want to make the training bike work properly with the 11spd cassette you will have to replace your right side shifter (shifter for the rear derailleur) with an 11 speed version or with a friction shifter. Also since (as pointed out by @Argenti Apparatus) the actuation ratio of 8 and 11 speed derailleurs are different, you will need to replace the derailleur with an 11 speed compatible derailleur. Removing a few cogs from the 11 spd cassette won't work due to the different cog spacing as long as you don't upgrade to an 11 SPD shifter due to the different spacing between the cogs. You can ride it but you won't be able to properly index it and the drivetrain will wear out faster and you probably won't be able to shift into some of the gears due to not being able to properly index it.

Do keep in mind 8 speed cassettes are a lot cheaper than 11 speed so the replacement parts (cogs or entire cassette, when the current cassette is worn) will be more expensive also.

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    Thank you Maarten for you tips. I had hoped I could take out some cogs, but alas.. Changing an entire shifter seems like alot more work/money/time. Guess I'll have to replace the entrie 11 speed casette to an 8 speed, maybe in the future my budget increases :)
    – nclsvh
    Dec 17, 2019 at 11:10
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    Well you only have to replace the shifter and Cassette to 11 speed so you can keep the original cables, derailleurs etc. If you get a second hand 11spd shifter it shouldn't be that expensive.
    – Maarten -Monica for president
    Dec 17, 2019 at 11:12
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    Friction shifters are also a cheap option but perhaps less desirable, you can get them in both indexed and non indexed versions (the latter should work with any number of cogs on the casette since there are are no distinct clicks/gears on the non indexed version). It is also infinitely adjustable so you will only have to adjust your derailleur limits and make sure cable is not too slack but the adjustment is a lot less precise)
    – Maarten -Monica for president
    Dec 17, 2019 at 11:16
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    @Maarten-Monicaforpresident 8 speed derailleurs cannot be used with 11 speed shifters. Shimano 11 speed systems use a different actuation ratio (ratio cable pulled to derailleur movement). SRAM use different ratios also.
    – Argenti Apparatus
    Dec 17, 2019 at 13:18
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    @nclsvh 8 speed cassettes are cheap is you hunt around on the Internet a bit. Also see of you have a bike co-op near where you live that has lightly used parts. Local Facebook bike marketplaces are a good source as you can create a post asking if anyone has a spare 8 speed cassette lying around.
    – Argenti Apparatus
    Dec 17, 2019 at 13:34
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You need an 8-speed cassette with the same large cog size as your bike is set up for and an 1.85mm cassette spacer to adapt it to your 11 speed wheel. Together those are about $20US.

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  • why would it be strictly necessary to have the same size large cog as on the original 8 speed cassette? Wouldn't a different size (larger) large cog be acceptable as long as the chain is long enough and the chain capacity of the derailleur is sufficient?
    – Maarten -Monica for president
    Dec 17, 2019 at 20:30
  • @Maarten-Monicaforpresident is correct, but perhaps Nathan just meant that the OP doesn't want a big cog that's bigger than the OP's bike's big cog. If it's an older 8s group, the derailleur may not allow for a cog over a certain size, whereas current Shimano Claris 8s cassettes appear to go up to 34t. In the era of 8s road groups, 34t was unimaginably large for a road bike. It might have been considered an MTB cassette. You could have incurred mockery if you'd cycled up to a group of racing cyclists with a 34t big cog!
    – Weiwen Ng
    Dec 17, 2019 at 21:02
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    Mr. Knutson's suggestion likely reflects a way to avoid issues with chain sizing and even indexing, while giving the OP what is the most simple and economical route should they desire to use both wheels. Typically a chain should be resized if there is more than a two-tooth change in the large cog of the cassette. Thus, a change from an 12-28t to an 11-32t, both fairly common 8 speed cassette options, requires adjustment of chain size and the rear derailleur's B-screw.
    – Jeff
    Dec 17, 2019 at 21:14

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