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Old 07-27-07, 09:48 AM   #1
AJU
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Chain Length

I have read Sheldon Brown's writeup on chain length (1 link beyond meeting around the biggest ring/cog), but have a question he didn't answer. What if I want to swap cassettes? How can I acheive a functional compromise? For example, I have a 48t large ring. I have a cassette with a 25 large cog and I have a cassette with a 32t large cog. Is there any way I can size the chain so I can use either cassette without modifying the length of the chain?
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Old 07-27-07, 09:57 AM   #2
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Probably not. Either too much or too little chain will cause shifting problems.

This is why multi-speed bikes exist, so you can have a range of gears. If you are going to need (or want) a 32 bottom end then get that and set your bike up for it correctly.
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Old 07-27-07, 10:01 AM   #3
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What about on the other end? What do you have on the high end of the cassette? I would think that if both cassettes have the same, or close to, high gearing, then it would work. A 32/12 and a 25/11 might work, I would think.
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Old 07-27-07, 10:16 AM   #4
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What about on the other end? What do you have on the high end of the cassette? I would think that if both cassettes have the same, or close to, high gearing, then it would work. A 32/12 and a 25/11 might work, I would think.
No.

The chain is cut to work with the largest ring & cog; the small cogs don't influence this process.
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Old 07-27-07, 10:23 AM   #5
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Not an issue.

Assuming your rear derailleur has the slack take up capability to handle the 32t cassette, just size it for that cassette and it'll work with the smaller one too.

If your derailleur doesn't have enough slack take up, I still think that it's better to size it for the largest possible combination. You might have some issues with the little/little combinations but those seldom come up when using a double crankset and they never come up with a triple.
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Old 07-27-07, 10:30 AM   #6
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It's a long cage XTR - I imagine it has enough take up
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Old 07-27-07, 12:19 PM   #7
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Originally Posted by AJU View Post
I have read Sheldon Brown's writeup on chain length (1 link beyond meeting around the biggest ring/cog), but have a question he didn't answer. What if I want to swap cassettes? How can I acheive a functional compromise? ... I have a cassette with a 25 large cog and I have a cassette with a 32t large cog. Is there any way I can size the chain so I can use either cassette without modifying the length of the chain?
Size it to the largest combo.

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Old 07-27-07, 02:35 PM   #8
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Thank you!
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Old 07-27-07, 06:58 PM   #9
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Size it to the largest combo.

Sheldon "Too Long Is Harmless" Brown
I wish we could get that idea across. For some reason so many riders thing a too long chain is as harmful as a too short one.
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Old 07-27-07, 07:28 PM   #10
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Indeed it's silly to say "It won't work" with the smaller range cassette, considering that a 25 tooth cog (or close) would be on the large range cassette. As long as the derailleur will handle the 32 you will have no problems. I went on a tour on a freewheel with a 28 larg cog, and changed to a 13-21 for a couple of races - ran great.
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Old 07-27-07, 07:49 PM   #11
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Since the OP's question appears well-answered perhaps it won't be thread-stealing for me to mention something I developed for switching around cogs on my Sturmey Archer 3-speeders. I cut my chain deliberately short and then make up a short (maybe less than 6" worth) splicing length of chain to bring the total length of the long section added with the "splice" section to the correct length for the particular cog. The 18T cog and the 22T cog each has its own different-length "splice" section. Of course this uese two master links and in the case of one of the two sets, a half-link IIRC.

So when I change from one cog to the other, I also change splice sections.

Geeze, I hope I explained that OK.
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Old 07-27-07, 09:34 PM   #12
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I wish we could get that idea across. For some reason so many riders thing a too long chain is as harmful as a too short one.
Well, neither is really "harmful".

To short can cause binding if you attempt to engage both large gears; too long can cause the cage to ride up on the cluster if you are in small-small.

Yes, these gear combinations are not recommended; I'm just fussy and like my bikes to work as well as possible.
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Old 07-28-07, 12:11 AM   #13
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No.
The chain is cut to work with the largest ring & cog; the small cogs don't influence this process.
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To short can cause binding if you attempt to engage both large gears; too long can cause the cage to ride up on the cluster if you are in small-small.
Except if both cassettes have the same small cog, there's no such thing as a chain too long for one but not the other. "too long" depends on the small/small combination, while "too short" depends on the big/big. As mentioned above, a 12-34 cassette will include a 25 cog (or close to it), so if the chain and RD can handle the larger combination, the smaller one will be fine.

Of course, we haven't heard yet if the smallest cogs are the same on both cassettes.
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