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Old 09-02-10, 10:27 AM   #1
|3iker
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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.
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Old 09-02-10, 10:36 AM   #2
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should be zero.
only around half the teeth of the cogs are ever engaged by the chain at once.
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Old 09-02-10, 10:48 AM   #3
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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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Old 09-02-10, 02:24 PM   #4
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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.
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Old 09-02-10, 03:03 PM   #5
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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..
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Old 09-02-10, 03:27 PM   #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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Old 09-02-10, 07:31 PM   #7
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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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Old 09-02-10, 11:37 PM   #8
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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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