# Bicycle Mechanics - How do you determine the right chain length

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.

09-15-10, 08:16 PM
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?

Bezalel
09-15-10, 08:26 PM
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

nhluhr
09-15-10, 09:26 PM
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.

thirdgenbird
09-15-10, 09:35 PM
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.

pacificaslim
09-15-10, 09:47 PM
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.

TimeTravel_0
09-15-10, 10:49 PM
chain stay length...as measured from what to what?

pacificaslim
09-15-10, 11:12 PM
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).

well biked
09-15-10, 11:13 PM
chain stay length...as measured from what to what?

Center of crank bolt (aka center of bottom bracket) to center of rear axle.

09-16-10, 05:25 AM
Thanks very much guys!

DaveSSS
09-16-10, 07:35 AM
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.

09-16-10, 09:04 AM
Chain stay is 410cm. Wow, big bike! ;)

Grand Bois
09-16-10, 09:19 AM
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.

nhluhr
09-16-10, 09:36 AM
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.

SBinNYC
09-16-10, 09:39 AM
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.

nhluhr
09-16-10, 09:41 AM
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.

DaveSSS
09-16-10, 12:04 PM

09-16-10, 06:39 PM
Good thoughts. Thanks!

thirdgenbird
09-16-10, 07:07 PM

technically this is correct. (at least it is in every other industry i am aware of)

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.