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Chain length help please(15 posts)

Chain length help pleaseColorado Ron
Sep 18, 2002 10:57 AM
I need more climbing gears so I'm going to try a XTR cassette, and Rear Derailluer on my road bike. I realize I will also need a new chain. My questions is, how do I know what length the chain should be? What should I look at to know the length is right?

thanks in advance
EasySpoke Wrench
Sep 18, 2002 11:03 AM
Bypass both derailleurs and wrap your chain around the big chainring and biggest cog. Add 1" of chain.
Once again,....Colorado Ron
Sep 18, 2002 12:17 PM
thanks for helping me out Spoke Wrench.
Easy, but not always wise...C-40
Sep 19, 2002 5:04 AM
Even if this method produces an acceptable length, it could result in a chain that is too short, it the cassete was changed from an 11-21 to a 12-25. If the chain was set with the 11-21 cassette, an additional inch of chain would be need to be added for a 12-25 cassette.

Setting the chain length to the maximum useable length in the little/little combination as I've described in my post, insures that you have the enough length to cover the entire range of the derailleur's capacity. Shortening the chain only reduces the derailleur's capacity and does not improve shifting.
Think about it this way, C-40.Spoke Wrench
Sep 19, 2002 5:52 AM
The method that I suggested yields the shortest chain that will safely cover the big/big combination that is on the bike. The length of the derailleur cage is irrevelant because, in in the big/big combination, the cage is nearly parallel to the chain.

Your way results in the longest chain that the derailleur will take up the slack in the little/little combination.

If you assume that the rear derailleur has adequate slack take up capability, it doesn't matter. Either will work.

Now assume the derailleur's slack take up isn't adequate. My way will result a slack chain that slaps the chainstay in the little/little combination. Your way results in a too tight chain that will bend the derailleur into the spokes.

I think that more people would rather ride home on a bike with a little chipped paint than suffer a ruined derailleur, rear wheel and maybe even a ruined frame on the road. I suspect that's why Leonard Zinn among others recommend the easy method that I suggested. It's wiser.
wrong, wrong,wrong...C-40
Sep 19, 2002 8:24 AM
The method that sets the change to the maximum useable length will never hang loose in the little/little combination, it also insures that all of the derailleurs capacity is available.

If you're stupid enough to use a cassette and chainring combination that exceeds the derailleur's capacity you get what you deserve. If you intentionally exceed the derailleur's capacity, several of the smaller cogs will not be useable with the little chainring. Once again, not real wise.

With my method, the chain length will never have to be altered to use any cassette within the derailleurs capacity. It's your method that risks making the chain too short if a cassette with a larger lowest cog is later installed without increasing chain length.

If you use a campy 10 system like I do, adding additional length to the chain means buying a new one. There is no safe way to add an inch to a any of the 10 speed chains. It's smarter to set the length to the maximum when it's new, then you can use any cassette from a 11-21 to a 13-26 without any fear of problems.
proof that it doesn't work...C-40
Sep 19, 2002 1:57 PM
I just tried your method on my campy 10 setup with a 12-25 cassette. You're right about one thing, your method can set the chain too long. Mine would be a full inch longer than I have it set and the chain would hang loose in the little/little combo. The proper length that maintains the derailleur's full capacity is an inch shorter.

If you read the details of the my method more carefully, you would note that the second test is the big/big combo. If you're too stupid to try this before hitting the road, you deserve the results.
I guess I was wrong.Spoke Wrench
Sep 19, 2002 3:07 PM
That's the chain sizing method that is recommended by virtually everybody. I thought it was idiot proof. If it didn't work for you though, maybe it isn't.
proof that it doesn't work...the other Tim
Sep 19, 2002 3:59 PM
So, what you're saying is that your method results in a chain that just reaches around the big-big combo with no derailleur, and uses all of the derailleur's capacity to wrap when on the small-small combo. And this is with a 12-25? How would a 26+derailleur fit? How would this work with an 11-26?

Take a look at your derailleur. Is Campagnolo spelled correctly?
slight recant...C-40
Sep 19, 2002 6:06 PM
A checked again and must correct myself. I forgot that my chain already had the "extra inch" because it was previously set to the proper length by the little/little method. So the big/big combo with an extra inch does work (my apologies), but the length is still only adequate to handle the maximum cog of the cassette with which it was set.

If you were to set the length with a 21T big cog and later change to a 26, bad things could happen. The required chain length is 1-1/4 inches more. That's why it makes no sense to me to shorten a chain to a length that is shorter than required to use the derailleur's full capacity. It would be OK if you never change cassettes.

As for your smart-ass comment, campy doesn't offer an 11-26, but the answer is simple. If you were smarter you would know that each tooth changed requires 1/4 inch of chain and the minimum increment of change in chain length is 1 full inch. A one tooth change on either end of a cassette should never create a need to change the chain length.

If the chain is set by campy's instructions (the little/little method) it automatically has sufficient length to handle a 26T cog. When in my 25T cog, there's plenty of travel left in the derailleur. It will also handle an 11T top cog without shortening, since there's only 1/4" difference in the length requirement. Next time load your gun before shooting.
apology accepted (nm)the other Tim
Sep 19, 2002 7:19 PM
optimum accuracy...C-40
Sep 18, 2002 6:44 PM
Methods that bypass the derailleur don't account for differences in the length between short cage and long cage derailleurs. Amore accurate method 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. 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.
optimum accuracy (proof-read)...C-40
Sep 18, 2002 6:48 PM
Methods that bypass the derailleur don't account for differences in the length between short cage and long cage derailleurs. A more accurate method 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. 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: Chain length help pleaseKen
Sep 20, 2002 10:02 PM
I put on a new chain on my Campy 10 speed bike. I used one of the methods Park Tool recommends for arriving at the correct chain length. The method I chose was to bypass the rear derailor and wrap the chain around the big ring and the big cog. Pull the chain tight and at the point where the chain forms a complete circle go over two links longer and cut the chain there. On my ride with a 53/39 front and a 13/29 cassette the chain length is spot on. Occaisionally I swap this cassette out for the 12/25 one and again no problems.
it works if...C-40
Sep 21, 2002 9:51 AM
you choose to set the length with the largest cog that will be used. If you would have set the chain length with the 12-25 it would have been and inch shorter. Then you could get into trouble when you put the 13-29 on.

That's exactly why campy directions make more sense. Using the little/little combo will always give you the longest chain the won't ever hang loose and gives you the full capacity of the derailleur.