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will a larger cassette work with my drivetrain setup?(6 posts)

will a larger cassette work with my drivetrain setup?AdamM
May 8, 2002 5:50 PM
I've got a 53-39 Ultegra crank and 12-23 cassette. I'm thinking that I would like a lower cassette for when I get out to the mountains. Should a 12-25 work or will I need to get a longer chain? Would a 12-27 just be overkill? I know thats an extremely subjective question but I wouldn't mind any feedback from people running those combos. My mountain riding is mostly going to be around Asheville NC if that helps any. thanks for any help

Adam
re: will a larger cassette work with my drivetrain setup?davet
May 9, 2002 4:38 AM
A 12-25 cassette will work just fine and most likely not need any additional chain length. A 12-27 is even better (in my hilly section of the country). I installed one on my bike and didn't need to do anything to the chain. Your bike may or may not need more chain, but if it does I would add a link (or two) rather than buy a whole new chain. If you do this, be careful and do a good job.
Be careful with chain length.Spoke Wrench
May 9, 2002 4:56 AM
I think that it's important to have a chain that is long enough to cover the big/big combination. If it's not and you accidentally try to shift into that combination, it can cause serious damage to your derailleur, wheel and frame.

There is a school of thought that you should keep a separate chain for each cassette. That way the wear patterns will always match. Since chains are about half the cost of a cassette, I see some value in that concept.
Be careful with chain length.atpjunkie
May 10, 2002 2:58 PM
you need to make sure your derailleur is med. throw to go to 12-27 I think. Check the specs on your derailleur first. Going 12-23 to 12-25 shouldn't need chain lengthening (I just did this surgery on my girlfriends bike) Put the bike on a stand and slowly pedal it, shift it into big ring/ big cog slowly, don't force it. If it goes easily and you have some play in the rear derailleur you will be okay. If it doesn't and rear der. is tight you need to add a link. If not, and it's sticky and you make that shift at the top of a climb you will
Break the derailleur
Break the derailleur hanger (expensive if its not a replacable one)
Probably throw the derailleur into your rear wheel and destroy it.
Most likely you will need to add a link to go 12-27, 12-25 should be ok.
Be careful.
setting chain length...C-40
May 11, 2002 1:31 PM
The following procedure will guarantee that the chain is long enough to handle any cassette within the derailleur's capacity.

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 overextending 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.
re: will a larger cassette work with my drivetrain setup?johnrg
May 11, 2002 8:41 PM
Get the 12/27. I also have the ultegra and on my last 2 bikes changed to the 12/27 without issues. Makes riding those mountain roads enjoyable.