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Old 08-02-10, 02:58 AM   #1
aljohn
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chain length for a triple

I've always fitted chains by trial and error, not clever but always worked OK. I see Zinn reckons loop chain round big ring and big cog, without going through derailleur, and add one complete link. I'll try this but it doesn't look like it will be long enough. Just thought I'd check what you guys think. I did try searching but I must be doing something wrong (what me?)
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Old 08-02-10, 03:27 AM   #2
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The obvious problem with this method is that it does not account for RD
cage length, and likely assumes a standard or mid length cage length,
ie shorter than triple cage length. I suspect you will need more chain
than one extra inch. Parktool.com has a long discussion with some
pix. The big-big method is a start, but will result in a completely
straightened RD cage for many setups, but particularly for longer cage
RD. It also can be problematic for some ATB setups where the BB axle
to rear wheel axle centerlines are not fixed lengths as the rear triangle
moves up and down.
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Old 08-02-10, 04:07 AM   #3
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Best way I have found is to put it on the big ring on front and the small sprocket on back but make sure you have it threaded on the RD.Then bring the RD at 6 0 clock to where they meet and cut if you need to then hook it up and you are done.Best way I have found.Takes all the guess work out of it.
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Old 08-02-10, 05:15 AM   #4
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I do it that way all the time and it works. Never caused me a problem. Can't understand what doesn't look long enough. If it goes around the two biggest what more could you want? It's the right thing to do.
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Old 08-02-10, 06:43 AM   #5
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There is no need to account for cage length. The 1 inch is added just to account for the length required to run the chain through the jockey wheels.

The big/big plus 1 inch method will work for any derailleur equipped bike, but it suggests the shortest possible chain.

I use the little/little method to insure a chain length that is the longest possible. Route the chain through the RD, as normal, and make the chain as long as you can without hanging loose or rubbing on the upper part of the RD cage. When the ends of the chain are brought together, the lower jockey wheel should swing down a bit, indicating that tension is being applied.

The only time that the little/litle method does not work is when a drivetrain is setup to exceed the RD's wrap capacity. Then the chain won't wrap the big/big. The big/big method would suggest a 1 inch longer chain, but then the chain will hang loose in the little ring and several of the smallest cogs. That's OK as long as you know that and don't use those combinations.

FWIW, one inch of chain equals 4T of wrap capacity.
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Old 08-02-10, 06:56 AM   #6
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There is no need to account for cage length. The 1 inch is added just to account for the length required to run the chain through the jockey wheels.
Absolutely agree that derailleur cage length is immaterial but I've always thought the extra 1" was to allow enough length for the chain to "climb" over the tops of the chainring and cog teeth when shifted into big-big. The tops of the teeth describe a larger diameter circle than the root diameter and the chain has to be long enough to reach that far out.
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Old 08-02-10, 07:34 AM   #7
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Absolutely agree that derailleur cage length is immaterial but I've always thought the extra 1" was to allow enough length for the chain to "climb" over the tops of the chainring and cog teeth when shifted into big-big. The tops of the teeth describe a larger diameter circle than the root diameter and the chain has to be long enough to reach that far out.

Perhaps a combination of both? It obviously require some length to go around the jockey wheels too. This guy thinks it's an allowance for the for the jockey wheels.

http://www.machinehead-software.co.u...engthcalc.html

I still prefer the little/little method, since I never use a combination that exceeds the RD's wrap capacity. I have one chain length that will work with any road cassette made by Campy, for my Campy drivetrain.
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Old 08-02-10, 08:00 AM   #8
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I still prefer the little/little method, since I never use a combination that exceeds the RD's wrap capacity. I have one chain length that will work with any road cassette made by Campy, for my Campy drivetrain.
Right, the limitation of the big-big method is if you change to a cassette with a larger large cog then the chain will certainly be too short.

However, I tend to routinely exceed the rear derailleur's published wrap capacity by switching 30T granny rings for 26T so I want the shortest possible safe chain length and I still have to avoid a couple of the small-small gears. Since I use 12x27 Shimano or 13x29 Campy cassettes, switching to a cassette with a larger big cog isn't going to happen.
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Old 08-02-10, 03:22 PM   #9
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Thanks for all the info, I'm glad I asked. I've just swapped all the components from one, larger, frame to my new one. The original chain fitted OK and seems to be working correctly. The largest cog is 23 so I will probably be fitting a new cassette and chain with a 27 0r 29 large cog. Hence my query.
I mentioned in a previous post that I have Campag Xenon rear mech and shifters, 9 speed and mech has a long cage. Front mech is a Campag comp triple, rings are 52/42/30. That gives me a 35" bottom gear, a little lower would be handy ;-) I shan't be rushing to do this too quickly, I want to ride my new/old bike for a while....
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Old 08-03-10, 10:39 AM   #10
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I've followed the instructions on Park's website (and also Sheldon's) and never had a problem. Are you sure you have the right rear derailleur?

When in doubt, take it to a good local mechanic. They'll sell you a chain and install it very reasonably. At least, my guy will.
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Old 08-03-10, 07:53 PM   #11
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I mentioned in a previous post that I have Campag Xenon rear mech and shifters, 9 speed and mech has a long cage. Front mech is a Campag comp triple, rings are 52/42/30. That gives me a 35" bottom gear, a little lower would be handy ;-) I shan't be rushing to do this too quickly, I want to ride my new/old bike for a while....
As I mentioned in my posting above, I changed the stock 30T granny ring on a Chorus Triple crank (originally 53/42/30) to a 26T which will give you a ~15% lower gear or about 30" with your current 23T large cog. Mine shifts fine with this setup but I do have to avoid any cog smaller than 16T with the new granny or the chain drags on the tail of the front derailleur cage. This is not a handicap.
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