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12-23 switching to a 12-27, do I need a longer chain?(7 posts)

12-23 switching to a 12-27, do I need a longer chain?853
Oct 8, 2002 6:52 AM
Want to just be able to change a wheel for hilly rides without messing with anything else. Is that possible?
dependsDougSloan
Oct 8, 2002 6:57 AM
I depends solely on how long your chain is now. It's easy to tell; put on the new cassette and shift to the big ring, then slowly shift to the 27 cog while on a work stand. If the derailleur pulls are pulled straight or twisted, or if it just won't shift, you need another link. Can't tell ahead of time without knowing how long your chain is now.

Doug
And if you do need a longer chain...Ray Sachs
Oct 8, 2002 7:22 AM
you can just leave it on when you go back to your 12-23. That won't create any problems. So then you'll just be able to swap wheels without having to do anything else.

-Ray
Thank you....853
Oct 8, 2002 8:40 AM
So the best thing to do is set it up the chain for a 12-27 and leave it as is for anything else. Thanks
and here's how to do it right...C-40
Oct 8, 2002 4:00 PM
The Ultegra derailleur has a 29 tooth capacity and will handle a 27T max. cog. To set the chain to the length that insures the full use of this capacity, set the chain length as follows:

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.

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 (one inch). Unfortunately, when you go to a 12-27, you lose the 16 tooth cog. You'll soon miss it.

Since you are going to use the largest rear cog that the derailleur can handle, you can also use another method that should produce the same result. Wrap the chain around the big ring and biggest cog, bypassing the rear derailleur. Bring the ends togther and add one inch. This method will only produce the maximum useable length with the largest cog that the derailleur will handle. If the length was set by this method with a 23 max cog, it would be too short for the 27, unless two inches was added.

Once you've set the chain to the proper length, you'll never have to change it. You can run anything from an 11-21 to a 12-27.
XTR rear derailleurDougSloan
Oct 8, 2002 7:42 PM
This is a bit off topic, but on my Cervelo I had problems with the Dura Ace derailleur running into the cogs if I used a 25 or larger. So, I put on an XTR long cage derailleur. Since I'm running a 56/39 combo up front, this allows me to use any gears I want to, with the chain set to maximum length in a 39x11 combination. I checked, and specs tell me the XTR is actually lighter than the Dura Ace. This seems odd, but that's what I read. The system shifts perfectly, and I never have to worry. Other than a little extra chain weight from a couple extra links, and every so slight great air drag from that longer cage hanging down, there is no drawback to this. I wonder why more people don't just throw on the XTR and never worry?

Doug
Another vote for XTRscottfree
Oct 9, 2002 6:00 AM
For general-purpose riding that includes hills, XTR is a superior derailleur. It works great, offers maximum flexibility in cogset selection -- and I now know it weighs less. Makes life simple. I have XTR on two of my road bikes, think it's the bee's knees, nearly as good as Suntour Superbe Pro.