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I have an 5800 set on my bike. However I changed the rear wheel, which comes with a Shimano FH-M756AL hub, which does not support the 11 speed cassette. So for now, I removed the 21 cog and added a spacer before the largest cog. So the shifting is kind of working, but I'm not 100% sure it is fine. I'm looking for a solution which does not require any hybrid cassette.

If I purchase a 5700 10 speed cassette will it fit on the hub and will it work with the ST-5800?

Or is there a MTB cassette that will work with ST-5800?

Thanks

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You can't use a stock 10-speed cassette with your 5800 shifters because the spacing will be wrong. There are two good options here:

  • Remove the 12t cog from an 11-speed road cassette. All (or almost all) the Shimano ones that start with 11 and go to 32 or less have 11-12-13 as the first three positions. Trading a one tooth jump for two teeth is negligible for almost all usage. In competition it's relevant, but you're ruining your wheel swappability by doing any of this so it doesn't belong on race bikes anyway. This trick works so well in practice that you can kind of read between the lines that it was there on purpose.
  • Get one of the 11-speed Shimano road rear derailleurs that can handle a 34t cassette and just set your bike up with 11-34. Good if you want that sort of gearing, but not if you don't.
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  • Can you please recommend parts for the second option? Derailleur and cassette. Also will the new derailleur work with the lever? Thanks
    – MetaImi
    Mar 8, 2020 at 20:43
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    RD-R7000-GS, CS-HG700-11 in 11/34, and CN-HG601-11. (You usually need a new chain when doing this and it's good to start a fresh one with a new cassette anyway.) All 11-speed Shimano STIs presently work with all 11-speed Shimano road RDs.
    – Nathan Knutson
    Mar 8, 2020 at 21:38
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Unfortunately you have no good solutions here.

There is no reason why the shifting should not work with a missing sprocket, you just have to get the indexing correct. The jump from 19 to 23 may be poor though. You may be able to prevent the shifter from shifting off the truncated cassette by winding the low limit in. This is obviously a kludge and you are missing a gear ratio.

You can't use a 10 speed cassette because the spacing of the sprockets is different on 10 and 11 speed cassettes. Also 10 and 11 speed chains have different external widths. See http://blog.artscyclery.com/science-behind-the-magic/science-behind-the-magic-drivetrain-compatibility/

Shimano retained the 10 speed freehub body width for 11 speed MTB groupsets. The reason this works is that the large inner sprockets can overhang the spoke flange slightly. Some Shimano 11 speed road cassettes can also do this, but they are all wide range models with 36 tooth or more (I think) large sprockets.

If you have a 5800 SS (short cage) derailleur the max large sprocket is 28, is you have a GS (medium cage) the max large sprocket is 32. See https://productinfo.shimano.com/download/?path=pdfs/archive/2017-2018_Specifications_v028_en.pdf, search for 'RD-5800'.

Really the only proper solution is to get a a wheel with an 11 speed hub.

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    The Shimano 11-34 11sp is supposed to fit on 10 speed hubs like the mountain bike cassettes. They have also expanded some of the GS derailleurs to cover the 34 tooth cog
    – Ross Millikan
    Mar 8, 2020 at 13:53
  • I've also read that the mid range derailleurs often work with the 34t cassette. This is somewhat dependent on the derailleur hanger mount point (Shimano supports a range and lower is better if one wants to fit a 34t cog). If additional clearance for the 34t cog is required people will install a longer B-screw.
    – NoCo Rider
    Mar 9, 2020 at 6:29

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