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Old 09-15-10, 08:16 PM   #1
Radix
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How do you determine the right chain length

I've got 108 links on there now - which is different than other chains I've had on there - all put on by mechanics. I have new chain that I know is way to long, and I'm wondering how many links I should take off. The chain I have on there works good enough, but the pulley grinds a bit (shimano 105 at it's limit with a 12-27 cassette). 30/42/52 rings up front. Chain stay is 410cm.

Would a longer/shorter chain help prevent the occasional grinding pulley?

Any advice appreciated!
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Old 09-15-10, 08:26 PM   #2
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My calculaters say that you have the correct size chain. If you want to replace your chain with a longer one first shift to 30/12 and make sure your derailleur can take up the additional slack
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Old 09-15-10, 09:26 PM   #3
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You wrap the chain around the large chainring and the large rear sprocket (do not thread it through the rear derailleur), and then add one more link. It comes out perfect every time.
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Old 09-15-10, 09:35 PM   #4
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Quote:
Originally Posted by nhluhr View Post
You wrap the chain around the large chainring and the large rear sprocket (do not thread it through the rear derailleur), and then add one more link. It comes out perfect every time.
i used to use the "classic" campagnolo method but switch to the above process on 5 builds (not all mine ) this summer and it works great every time. i used it for 3 standard road setups, a compact, and a road triple.
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Old 09-15-10, 09:47 PM   #5
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You can use this formula as well (courtesy of Park Tool's website):

L = 2 (C) + (F/4 + R/4 + 1)

L = Chain length in inches. Round the final result to closest whole inch figure.
C = Chain stay length in inches, measure to closest 1/8”, convert to decimal.
F= Number of teeth on largest front chainring.
R= Number of teeth on largest rear cog.
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Old 09-15-10, 10:49 PM   #6
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chain stay length...as measured from what to what?
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Old 09-15-10, 11:12 PM   #7
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Mount the wheel and then measure middle of rear axle to middle of bottom bracket (i.e. center of the bolt that's holding your crank on).
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Old 09-15-10, 11:13 PM   #8
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chain stay length...as measured from what to what?
Center of crank bolt (aka center of bottom bracket) to center of rear axle.
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Old 09-16-10, 05:25 AM   #9
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Thanks very much guys!
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Old 09-16-10, 07:35 AM   #10
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Quote:
Originally Posted by nhluhr View Post
You wrap the chain around the large chainring and the large rear sprocket (do not thread it through the rear derailleur), and then add one more link. It comes out perfect every time.

You add two links (1 inch) if the ends that come together are oppsites and can be joined. If they are the same, then add 3 links.
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Old 09-16-10, 09:04 AM   #11
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Chain stay is 410cm.
Wow, big bike!
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Old 09-16-10, 09:19 AM   #12
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You add two links (1 inch) if the ends that come together are oppsites and can be joined. If they are the same, then add 3 links.
One link is one inch. You are referring to half links.
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Old 09-16-10, 09:36 AM   #13
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One link is one inch. You are referring to half links.
I started to say exactly the same thing, but then realized chain manufacturers refer to a single link as the half-inch section. A standard new chain being 110 links is not 110" long. But yeah, the "wrap around big/big and add one" means add one 1" section.
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Old 09-16-10, 09:39 AM   #14
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Chain length depends on use. A racer wants the shortest possible chain length because it makes for faster shifts. The tourist wants the longest possible chain because in the event of a broken link, he can remove it and continue with his journey.

The method described above (big/big + 2 links) gives you the shortest chain length that should not break the RD.

To find the longest possible chain that will work: wrap the chain through the RD and the small cog and small chainwheel. Find the longest chain length that will still cause the RD to wrap some chain. You're now guaranteed that the RD will always take up chain slack.

The derailleurs will function with any chain between the minimum and maximum lengths. Your choice depends on how many times you anticipate breaking the chain and how inconvenient it might be to replace a broken link if you do break one.
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Old 09-16-10, 09:41 AM   #15
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Chain length depends on use. A racer wants the shortest possible chain length because it makes for faster shifts. The tourist wants the longest possible chain because in the event of a broken link, he can remove it and continue with his journey.
I would rather carry a couple links of chain with the chain tool than have a sloppy loose chain.
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Old 09-16-10, 12:04 PM   #16
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Quote:
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One link is one inch. You are referring to half links.

Chains are advertised as having 112 or 114 links. That makes a link 1/2 inch. Find me a chain that is advertised as having only 56-67 links.
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Old 09-16-10, 06:39 PM   #17
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Good thoughts. Thanks!
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Old 09-16-10, 07:07 PM   #18
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Quote:
Originally Posted by Grand Bois View Post
One link is one inch. You are referring to half links.
technically this is correct. (at least it is in every other industry i am aware of)

Quote:
Originally Posted by nhluhr View Post
I started to say exactly the same thing, but then realized chain manufacturers refer to a single link as the half-inch section. A standard new chain being 110 links is not 110" long. But yeah, the "wrap around big/big and add one" means add one 1" section.
Quote:
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Chains are advertised as having 112 or 114 links. That makes a link 1/2 inch. Find me a chain that is advertised as having only 56-67 links.
while bicycle chain is sold this way, Grand Bois is correct. in industrial applications chain is measured in number of pitches. an industrial engineer would tell you that i bicycle chain is 112 or 114 pitches long or 56-67 links. in this environment a "half link" for a bicycle chain would be a 1/2in section.

what a cyclist calls a half link would be referred to as an offset link:




why are these two environments different? i have no idea
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