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  1. #1
    Senior Member bluenote157's Avatar
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    max cog on a tiagra 9speed rear derailleur? rd-4400 short cage..

    came across this and thought about putting it on my beater town cx/commuter. Whats the biggest cog I can go on this? 27t?

  2. #2
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    Shimano specifies a 27T large cog as the maximum for their road rd's but experience says that up to 30T is almost always doable. Your short cage rd will accept the same maximum cog as a long cage, it just won't wrap up as much chain so the total gearing range can't be as large.

  3. #3
    Senior Member bluenote157's Avatar
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    gotcha! thanks hillrider.

  4. #4
    cab horn
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    Quote Originally Posted by HillRider View Post
    Shimano specifies a 27T large cog as the maximum for their road rd's but experience says that up to 30T is almost always doable. Your short cage rd will accept the same maximum cog as a long cage, it just won't wrap up as much chain so the total gearing range can't be as large.
    27t is based on an assumed hanger length. Some bikes will not take even a 25 even if the r.d specifics 27t.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  5. #5
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    Quote Originally Posted by operator View Post
    27t is based on an assumed hanger length. Some bikes will not take even a 25 even if the r.d specifics 27t.
    Correct but the great majority of frames will clear the 27 and a bit more so one that won't is an exception, hopefully a rare exception.

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