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Switching from 12-23 to 12-27, do I need to lengthen chain?(6 posts)

Switching from 12-23 to 12-27, do I need to lengthen chain?Uprwstsdr
Jul 16, 2003 9:31 AM
The chain is new, less than 250 miles on it.

Jul 16, 2003 9:38 AM
But you'll likely need to tighten the "B" screw on the back of the deraileur. Your pulleys will be too close to the 27 cog and rub if you don't.
Jul 16, 2003 9:57 AM
you might have to get a new chain, but it depends on how much "extra" chain you have right now. heres a link to the park site telling you how long yoru chain should be.
Jul 16, 2003 9:58 AM
Once you put on the 27, with the bike on a repair stand, try to go big-big. If it jams, you can either lenghten the chain or you can hope to remember not to go big-big. If you hope to remember, and you don't, it will cost big-big money to repair.
re: Switching from 12-23 to 12-27, do I need to lengthen chain?Roger H
Jul 18, 2003 10:20 PM
I did the same switch and lengthened my chain. I figured better safe than sorry.
mostly wrong answers...C-40
Jul 20, 2003 3:40 AM
Adding 4 teeth to the cassette requires 1 inch of additional chain wrap, but whether the chain needs to be lengthened depends on how the length was originally set. If it was done properly, you would not need to lengthen the chain. If the chain was set to the minimum length on the 53/23 combo, then it would need 1 inch of additional length.

Here's the correct way to set the chain length to insure the maximum capacity of the derailleur is available:

Two simple tests will determine if the chain is the correct length. First, it must not hang loose in the little ring, little cog combination. If there is no tension on the chain in the little ring, little cog combination, remove two links (one inch) at a time, until there is. When the ends of the chain are brought together, some movement of the lower pulley should occur, indicating tension is being applied. Two more links (another inch) may need to be removed, beyond the point of absolute minimum tension, to keep the chain from rubbing on itself as it passes under the upper derailleur pulley. Once this is done, the chain is set to the maximum useable length. Removing additional links will do nothing but reduce the derailleur's capacity. It won't help keep the chain from skipping or jumping.

Second, the chain must be long enough to avoid over-extending the rear derailleur when shifted to the big ring and biggest cog combination. If the chain is set to the maximum length as described, it should always pass this test, unless your setup exceeds the derailleur's stated capacity.

If you want to see how much lower pulley movement will occur, without removing the extra two links, shift up four teeth (11 to 15 or 12 to 16). This has the same effect as removing two links.