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· POGUE MAHONE
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I'm changing my 12/25 to a 12/27....I have a 39/53 with a 105 -FDR and an Ultegra RD.
Will I have to add a link to the chain length or will I notice any difference in shifting using my existing chain length....opinions?
 

· Cycling induced anoesis
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Export A said:
I'm changing my 12/25 to a 12/27....I have a 39/53 with a 105 -FDR and an Ultegra RD.
Will I have to add a link to the chain length or will I notice any difference in shifting using my existing chain length....opinions?
We have the same front der/ rear der and 39/53 set up, and I went from an 11-28 to a 12-25 without making a change in chain length. All that was required were minor adjustments to cable tension, but that could've been because it was a new build.

Easiest thing to do is try it and see. If you encounter problems then add a link, but with such a small change, I doubt you'll need to.
 

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Going to a larger biggest rear cog without adding a link may give you problems if you cross-chain (big ring, big cog). A common way to set chain length is to loop it around the big ring and big cog without lacing the chain through your derailleur. pull it taught and add one link to its taught length. If you think of chain length in these terms, what you'll see is that by increasing the big rear cog, you increase needed chain length. Now the caveat is that you shouldn't be cross-chaining anyway, and it's only on the big-big combinations that the length would be too short. In other words, you can probably get away with the same length, but when the time comes to change your chain (I get 2000 miles or so before it stretches too much, but that's another thread), you should measure it afresh.
 

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the best way...

The best way to set chain length is in the little/little combination. Make it as long as possible, but not hanging loose of rubbing on the RD. Then it will handle ANY cassette within the RD's wrap capacity. There is no resaon to change chain lengths unless you switch from a standard to compact crank.

Setting the length by any method that uses the largest cog will produce the same length if the cassette has the largest cog in RD's range. Otherwise, it may suggest a shorter length.

I takes four additional teeth to require one more inch of chain (the minimum increment of change).
 
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