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  1. #1
    Alfredo Contador |3iker's Avatar
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    42t --> 39t: # Chain links reduced?

    I am going to replace my 42t with a 39t. Just wondering if someone can provide me a calculation or to determine how many chain links should be reduced to compensate?

    The rear cluster is 12-25.

  2. #2
    AEO
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    should be zero.
    only around half the teeth of the cogs are ever engaged by the chain at once.
    Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
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  3. #3
    Senior Member Retro Grouch's Avatar
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    Why that's easy. Shift into the little/little combination. Unless the lower run of your chain goes slack, you're good-to-go.

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    Is the 42T chainring on a single chainring crank and being replaced by a 39T or is it one ring of a double crank and the 52 or 53T big ring is going to remain unchanged? If it a double, there will be no change in the chain length at all since the big-big combination hasn't been changed.

    If you are replacing a single 42T chainring with a single 39T you can, in theory remove 1 half link, but since this is impossible while having the mating ends of the chain still match, the chain must remain the same even in this case.

  5. #5
    coprolite fietsbob's Avatar
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    There are half links for 3/32 chains , but really that is useful with a standard 5 or 6 speed rear cog cluster.

    I'm using one on each my 2 bikes with internal gear hubs, and 3/32" chains, but they dont shift sideways..

  6. #6
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    Quote Originally Posted by Retro Grouch View Post
    Why that's easy. Shift into the little/little combination. Unless the lower run of your chain goes slack, you're good-to-go.
    Agreed. Unless there is a functional reason there's no reason to mess with a properly operating chain for that little a difference.

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    Quote Originally Posted by fietsbob View Post
    There are half links for 3/32 chains , but really that is useful with a standard 5 or 6 speed rear cog cluster.

    I'm using one on each my 2 bikes with internal gear hubs, and 3/32" chains, but they dont shift sideways..
    I thought the half-links (actually a half-half-link) was mostly used to adjust chain length on fixies and single speeds built on frames with vertical dropouts.

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    Senior Member Deanster04's Avatar
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    Quote Originally Posted by HillRider View Post
    Is the 42T chainring on a single chainring crank and being replaced by a 39T or is it one ring of a double crank and the 52 or 53T big ring is going to remain unchanged? If it a double, there will be no change in the chain length at all since the big-big combination hasn't been changed.

    If you are replacing a single 42T chainring with a single 39T you can, in theory remove 1 half link, but since this is impossible while having the mating ends of the chain still match, the chain must remain the same even in this case.
    Amen.

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