Chain length ok?
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Chain length ok?
I have a setup of 39/53 in the front and 12-25 in the back with the chain length cut to the specified. Will I have to get a new, longer chain, if I will replace the rear with a 13-28 cassette (front would remain 39/53) or will the chain residing on the bike now be of an adequate length? I have searched, and only found answers for a cassette size 12-27 replacement.
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1.5 tooth difference in chain wrap length.
3 possibilities,
prior chain had enough slack that it will be fine
install a half-link
stay out of big/big gear combo
3 possibilities,
prior chain had enough slack that it will be fine
install a half-link
stay out of big/big gear combo
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#4
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About the only way you could get by safely is if the fractional part of your link was nearly an inch long. IOW, you had something like 1-7/8 link sets slack.
That might be too tight for good shifting, but it should prevent damage if you go BIG:BIG.
That might be too tight for good shifting, but it should prevent damage if you go BIG:BIG.
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That's what I think too. You can ride along avoiding the big/big for a long time. Some sunny day, however, when everything is going wonderfully, you'll try to push up a little hill in the big ring and do $400 or $500 damage to your bike in the blink of an eye.
#6
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There are several problems here. You have no idea how the chain length was set, currently. You must have enough length to wrap the big/big. Ideally, you should have enough RD wrap capacity to handle any gear combination. You have three more teeth to wrap, when in the big/big and that requires .75 inch of chain. If the chain length was set using the big/big method, it will be too short.
If the chain has seen much use, then it really should be changed for a new cassette. Then you can use the big/big plus 1 inch method to ensure adequate length. If the chain hangs loose in the 39/13, then the RD has inadequate wrap capacity. If the big/big method is used and the ends of the chain that come together can't be joined (two sets of inner or outer plates) then you must add 1-1/2 inch or three links. This possibility is often overlooked in most chain length setting instructions.
I try to always use a RD with adequate wrap capacity and use the little/little method of setting the chain length. With that method, you make the chain as long as possible, while still maintaining a minimum tension. This method produces the maximum wrap capacity.
If the chain has seen much use, then it really should be changed for a new cassette. Then you can use the big/big plus 1 inch method to ensure adequate length. If the chain hangs loose in the 39/13, then the RD has inadequate wrap capacity. If the big/big method is used and the ends of the chain that come together can't be joined (two sets of inner or outer plates) then you must add 1-1/2 inch or three links. This possibility is often overlooked in most chain length setting instructions.
I try to always use a RD with adequate wrap capacity and use the little/little method of setting the chain length. With that method, you make the chain as long as possible, while still maintaining a minimum tension. This method produces the maximum wrap capacity.
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This is obviously the ideal way to go. However, if you, as I do, use a triple crank, even a long cage road derailleur, a wide range road cassette and change the original granny for a smaller one you are going to exceed the derailleur's wrap capacity and eliminate the use of small-small. The chain MUST allow big-big for safety reasons. Sacrificing small-small is no problem and inadvertently shifting into it is just noisy, not damaging.
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"If the chain hangs loose in the 39/13" don't use that gear combination, you are cross-chained and there are better combinations with nearly the same ratio. A loose chain won't damage your bike, a too-short one will.
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It is good practice to replace the chain when you replace the cassette. In theory at least, depending on how much use the present chain has had, that should result in a longer life for the new cassette, which is the more expensive item of the two, so my point is - why would you not? I am a little surprised that no one else mentioned this, although it is not strictly an answer to the question you asked. I usually pay no more than about $20 for a chain. Cheers.
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Thanks to all who took their time to write their suggestions. After weighing things out, it will seem logical for me to purchase a new chain (the cassette is new as well) to be sure of the proper length and to avoid complications.