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Chain Length(11 posts)

Chain LengthPete
Mar 7, 2001 8:11 PM
A 7700 chain has 116 links. How many do I need for a 39/53, 12x27.
re: Chain LengthAkirasho
Mar 7, 2001 11:57 PM
Take a look at this link.

I've used this formula with good success.

LONG Formula L = 2(C)+F/4 + R/4 + [(F – R) 2 · (0.0255)] · (1/ 2)·(1/C) + 1

L = chain length in inches. Round the final result to closest whole inch figure. Remember to round up from 0.5.
C = Chain stay length in inches, measure to closest 1/8".
F= Number of teeth on largest front chainring.
R= Number of teeth on largest rear cog.
(Note: The truly accurate formula includes "2 x pi" as part of the denominator under (F-R) squared. An approximation of 0.0255 is substituted in the interest of simplification.)

For example, a bike has a 53 front ring and a 24 largest rear cog. The distance between the crankarm bolt and the rear axle is 15-7/8", which using the chart below converts to 15.875".

L = 2(15.825) + 53/4 + 24/4 + [(53-24) 2 (0.0255)] · (1/2 · 1/15.825) + 1
L = 31.65 + 13.25 + 6 + (21.45) (0.0316) + 1

L = 52.68

This is rounded to 53 inches. If the simplified formula were used, the length would have been 52 inches, one inch too short. Check the largest front and largest rear cog before determining which formula to use.

Be the bike.
Or for a technique real people can use...Cory
Mar 8, 2001 8:12 AM
I'm willing to take Akirasho's word for all that, but an old rule that still works is this: Put the chain around the big ring and the big cog on the cassette and add one link.
Or for a technique real people can use...Pete
Mar 8, 2001 8:34 AM
with/without Derailleur?.dave hickey
Mar 8, 2001 10:51 AM
Cory, Is that with or without the rear derailleur?
110 links?Dog
Mar 8, 2001 8:43 AM
If your chain stay is relatively short (your tire is close to your seat tube), it's going to come out to 110 links for 53/27 combination, short cage derailleur. This is not absolute, but just for a double check reference point.

Shimano chain length specificationBipedZed
Mar 8, 2001 9:14 AM
Shimano suggests placing the chain through the rear derailleur and the big ring/small cog. Adjust the length so that the 2 derailleur pulleys are perpendicular to the floor (90 degrees). This allows you to use cassettes from 11x21 to 12x27 without having to adjust chain length.
simple method...dave
Mar 9, 2001 1:18 PM
Wrap the chain over the little chain ring and the smallest cog, and through the derailleur. Remove links until the lower pulley on the rear derailleur barely begins to swing down, when the ends of the chain are brought together, then remove one more link. This will give you the longest possible length, without the chain hanging loose.

If you want to see how much lower pulley movement will occur, without removing the extra link, shift up two teeth (11 to 13 or 12 to 14). This has the same effect as removing one link.
Another simple way!Bil J. Pappas
Mar 9, 2001 2:02 PM
The way that has always worked for me is this: Thread the chain on the big ring,through the rear der. and smallest cog i.e 53X12. The rear derailleurs' jockey wheels should be somewhat perpendicular to one another, when the chain is the correct length, and on the 53X12.
but not as accurate....dave
Mar 10, 2001 5:28 AM
I know this method has been recommended for at least 15 years, but...

Depending on the derailleur design and cage length, this method may or may not be relevant, and is more sujective. Setting the chain to the minimum tension in the little/little combo assures that maximum derailleur capacity is achieved.
220, 221 Whatever it takes.grz mnky
Mar 9, 2001 3:08 PM
Best way to tell is to cross shift (big/big) the bike, feed the chain on, then cross shift the other way (small/small) and make sure it's not too slack. You'll find that you have one or two choices. Err on the long side, then make it shorter if it's obvious that it's too long. Even though you don't want to really ride cross shifted you need to have enough chain to do it so when you brain fart near the end of a long ride you don't tweak the rear der. or possibly bend the hanger.