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determining chain length for 12-27(4 posts)

determining chain length for 12-27mr_spin
Jul 23, 2002 2:40 PM
I'm doing ride this weekend for which I am putting on a Dura Ace 12-27 cassette and a new chain. Right now I have a 12-25, so I'm guessing the chain length is similar if not the same, but I've read that the 27 needs a few extra links.

I looked up instructions for determining chain length and they all say put the chain in the small cog and large ring and bring the ends togther.

This doesn't seem right to me. It ignores the size of the largest cog, which in my view is an important consideration!!! Could the chain length for 12-23, 12-25, and 12-27 really be the same?
re: determining chain length for 12-27Chen2
Jul 23, 2002 2:49 PM
It probably needs to be the same length as for the 12-25. Run it around the small chain ring and the small cog and threaded through the rear derailleur. Shorten the chain just enough so that the rear derailleur is applying some tension to the chain. Then shift to the big and big combination. The rear der should not be at its limits in either the big - big or small - small combinations, not that you would intentionally use those, but just in case.
~Al
Chen2 is right, mr_ spin.Fredrico
Jul 23, 2002 5:33 PM
An even simpler way to adjust chain length is to put it in the smallest cog front and back, and take out links just to the point the chain-wrap on the UPPER jockey wheel clears the chain as it goes on the LOWER jockey wheel coming from the front chainring.

This is the longest the chain can be without rubbing at the rear derailleur pulleys when on the smallest sprockets front and rear.

The longer the chain, the "looser" it is, the slower it will wear out, along with the sprockets. The less tension, the better. You can actually feel too much chain tension pedaling.

Ciao,
Fredrico
http://www.totalbike.com/repair/chain.htmlcoonass
Jul 23, 2002 7:03 PM
nm