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I'm thinking about changing my 2nd chanring to a smaller one (2 chanring setup). I hear most people recommend to change the chain when changing the cassette.

Hence my question: should I expect to change other parts (chain? other chainring? cassette?) if I change my 2nd chainring?

Thanks

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up vote 3 down vote accepted

It would be wise to check the chain wear with a chain "stretch" gauge and replace it if the chain is beyond 0.75 or 0.8. Re the rear sprockets, they're only likely to be a problem if the current chain is worn beyond 1.0 stretch.

The other thing to worry about is whether the derailers can simply handle the difference. The rear derailer has a "tooth range" in terms of the greatest difference between the sum of tooth counts of the largest sprocket pair and the smallest, and if that range is exceeded then the chain will either go slack on the smallest combo or become over-stretched on the largest.

Further, the front derailer has a limit to how great a tooth difference it can handle, and too much difference could result in the chain rubbing the derailer or iffy shifting.

But these problems are only likely if the difference in old and new ring diameters is substantial.

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If you think your chain is not so new, you can put a new chain with the new ring and spare the current chain. Then, when you have to replace the chain, you put the not-so-old chain back. That way you don't expose a new ring to a not-new chain, and get every possible mile out of both chains. –  heltonbiker Mar 12 '13 at 2:30
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It depends on how worn out your old chainring and the other involved components (chain, cassette) are. If the chain and cassette are not that old that they would need to be replaced anyway, I would take the risk and change only the chainring first.

But there could be another thing that maybe needs to be changed: if you use a smaller chainring it may happen, that the chain will rub against the lower end of the dereilleur cache. Therefore it may be necessary to move the dereilleur a bit downwards on the frame.

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Which symptoms would I see, if my other parts are too worn out? Good point about the dereilleur. –  sorenkrabbe Mar 10 '13 at 18:08
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@sorenkrabbe If one or more of the parts is worn out too much, you will experience some chain skipping, as described in bicycles.stackexchange.com/q/12726/5271 –  Benedikt Bauer Mar 10 '13 at 22:11
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