|sizing a chain||mila|
Jun 1, 2001 5:21 PM
|I am in the process of changing out my 8 speed ultegra cassette with a new one as well as a new chain. I'm going from 11-21 to 12-25. The new chain is of course quite a bit longer than the old one. the old one had stretched somewhat. How do I get the chain length right given the extra teeth. I assume it will have to be a little longer than the old one, but how much, I'm not sure. Is it just trial and error (the new HG-92 chain came with two pins) or does someone know what length it should be. the front is 42/52.
Jun 2, 2001 1:30 PM
|The cog's teeth are 1/2 inch pitch. Two teeth equals one chain link. Even though the chain is 1/2 inch pitch, you can't remove half a link, the ends won't match up.
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, one link 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. On some derailleurs, one more link may need to be removed, beyond the point of absolute minimum tension, to keep the chain from rubbing other parts of the derailleur.
Second, the chain must be long enough not to overextend the rear derailleur when shifted to the big ring, and the biggest cog combination. If the the chain passes the first test, it should always pass this test, unless you're using a big cog which exceeds the derailleur's stated capacity.
Hopefully, you know that you should not use either extreme gear combination during normal riding. The big-big and little-little combos are a no no.
Jun 2, 2001 6:36 PM
|thanks for the info|
|What I did.||johnrossi808|
Jun 4, 2001 7:14 PM
|After reading the Zinn bike maintenance manual, I placed the chain in the big chainring in front and smallest cog in back. Then I lined up the jockey wheels of the rear derailleur vertically. I installed a Sachs chain on my bike using this procedure and everything was alright.|| |