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I am looking to replace my 11-30 Shimano 8000 to 11-34 hg800 cassette. My current chain is 108 links with my 11-30 and works fine. Would this be long enough for the 11-34 cassette without changing the chain (its new anyway)?

My crankset is 52-36 and my chainstay length is 405mm. I have seen online calculators and they say 108 links, I want to make sure if this correct?

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  • Generally, a new chain would be used if installing a new cassette as a worn chain on a new cassette will wear the cassette out prematurely (and a worn cassette will wear a new chain prematurely). Only reason not to would be if you had a near new chain on an unworn cassette. It might be prudent to change the chain anyway.
    – mattnz
    Sep 2, 2023 at 22:03
  • How worn is your current chain? Are you trying to re-use it because it is almost new? When you originally sized it, did you save the take-off links?
    – Criggie
    Sep 2, 2023 at 22:57

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It will also depend on the design of your derailleur. Any useful calculator would have to take that into account. But I'm sceptical of trying to calculate it. 4 teeth bigger on the big sprocket means an extra 2 teeth on the approximately semi-circular engagement, so 2 more links.

108 link chains are harder to find than slightly longer ones, so it's better to get a common 112 link chain and shorten it to fit. Or buy the cassette, see if the old chain is long enough, then buy the right new chain.

Assuming multiple chainrings, you should be able to cross-chain into the big/big combination that you wouldn't normally use, without the drivetrain jamming, but taking up essentially all the slack.

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  • Its the MD R.D. Cage I have 8000 Utegra
    – Jon.H
    Sep 2, 2023 at 15:03
  • The 108 link chain is the size I have on my bike and its shimano 105 114 11 speed I have which was cut to size to 54 links (54x2=108) link chain.
    – Jon.H
    Sep 2, 2023 at 15:07
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    +1 on this answer. Online calculators for this basically are ill-conceived for recent rear derailleurs; the rules for chain length used to be simpler. To OP: not intending to use the 52/34 is not relevant. What is relevant is how willing you are to break your bike if you shift into it by accident. Sep 2, 2023 at 18:02
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    @DanGao chain links are one per tooth, because they're really half links but no one ever calls them that. Therefore you can't remove a single link, only a pair (aside from unusual parts used in dome singlespeed setups). So in that standard terminologu, you need 2 more links to go jalf way round the sprocket, as I said. You're right, that means they're not available elsewhere in that case. I have all the tools, and can size a chain, so you seem to be confusing me with the OP.
    – Chris H
    Sep 2, 2023 at 19:11
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    Apologies Chris, I was attempting to reply to Jon.H. Jon., I'm not suggesting you remove anything. I'm pointing out that changing your cassette will eat up another link (two half links, Chris;-), so if you eyeball your current set up with one link squeezed out of the chainline, you can see how tight it wraps. Never "intending to use" the big-big is different than never finding yourself there. However briefly. In the long run you will need chain tools sooner or later.
    – Dan Gao
    Sep 2, 2023 at 19:45

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