I purchased a Merida Speeder 400 a year back. This came with Shimano 50-34 teeth and Shimano CSR7000 11-32 teeth 11-speed cassette which I replaced with Shimano 105 R7000 11 Speed 11-34 Teeth Cassette. Since then, the ride is not quite right. It feels like the chain is about to break sometimes especially in certain gears. What am I doing wrong?

  • 2
    Did you switch the chain for a longer one? If it came with 32, it should be fine with 34. You should have R7000-GS. Apr 12, 2021 at 17:55
  • @VladimirF I did not switch the chain for a longer one. I only changed the cassette. The bike came with 105-GS derailluer in the back but only 105 in the front. I think the size of the bike is S. The config can be found here. merida-bikes.com/en/bike/655-857/speeder-400 Apr 12, 2021 at 18:05
  • The two cassettes are fully compatible. The 11-34 cassette should have come with a small spacer that you would place behind the cassette only if you had an older wheelset that's supposed to be 10s compatible and not 11s. If you installed that spacer, you should remove it. If not, you'll need to be more specific about what you mean by the chain is about to break.
    – Weiwen Ng
    Apr 12, 2021 at 18:51
  • 1
    @Weiwen Ng Wouldn’t you WANT to use the spacer with a 11-34 on an 11s freehub? The 11s freehub is longer and so needs a spacer to take up the gap.
    – MaplePanda
    Apr 12, 2021 at 20:14
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    Check your B screw. Your derailleur may be interfering with the cogs if you didn’t adjust it. You also may need to re-index and adjust limit screws.
    – MaplePanda
    Apr 12, 2021 at 20:14

1 Answer 1


Shimano's published method for establishing chain length is based on adding links to the length that will wrap around large/large sans derailleur. When a bigger cassette is swapped in on a chain sized that way, the chain will typically be too short, and breaking your chain, derailleur, hanger, and/or frame may result.

The alternative is to do the technically wrong thing and size to allow the RD's entire total capacity to be used, which allows any cassette the RD would otherwise be compatible with to be swapped in. (The b-tension would need to be adjusted for it to work right, but typically things won't blow up even if that step is skipped.) There are those of us who feel sending riders out with a chain sized this way is doing them better service on average than giving them whatever marginal upside there is with fewer links. This practice can really save a lot of pain. And, if you're a mechanic, you have to think about who the finger is going to be pointed at when a 25 or 27 gets swapped on when the chain was sized for a 23 and someone's race/bike/life gets messed up because of it.

It's possible what you're describing is from not adjusting the B screw, but more likely it's from the chain being too short.

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