Chinertown

Other Resources => Maintenance, Mechanics, & Tools => Topic started by: Rajmundx on February 24, 2026, 07:20:19 AM

Title: Formula for the length of a chain (?)
Post by: Rajmundx on February 24, 2026, 07:20:19 AM

Is there a proven formula for calculating what length the chain should be shortened to?
I have a Shimano 50–34 crankset and a 12–32 cassette, and the chain I purchased has 126 links.

Title: Re: Formula for the length of a chain (?)
Post by: Da11as on February 24, 2026, 07:44:25 AM

Just check Shimano manual?
It hugely depends on the type of derailleur and chainstay length. For 2x it is safe to pull the chain across biggest ring and biggest cog (circumventing the rear mech), close the chain circle and add 2 links. If you have too much slack during the ride you may dare to shorten it by 1 link. 126 links is very long and you probably need less than 114 links.

Title: Re: Formula for the length of a chain (?)
Post by: Rajmundx on February 24, 2026, 07:53:01 AM

Quote from: Da11as on February 24, 2026, 07:44:25 AM

Just check Shimano manual?
It hugely depends on the type of derailleur and chainstay length. For 2x it is safe to pull the chain across biggest ring and biggest cog (circumventing the rear mech), close the chain circle and add 2 links. If you have too much slack during the ride you may dare to shorten it by 1 link. 126 links is very long and you probably need less than 114 links.

I just used the big chainring + 2 links method and the chain came out too long. I read somewhere that I’m supposed to shorten it to 108 links — is that possible?

Title: Re: Formula for the length of a chain (?)
Post by: SirBikealot on February 24, 2026, 08:17:24 AM

Quote from: Rajmundx on February 24, 2026, 07:53:01 AM

I just used the big chainring + 2 links method and the chain came out too long. I read somewhere that I’m supposed to shorten it to 108 links — is that possible?

i used this site for my 54-32 and went with 110 links on a 410mm chainstay.
https://www-bergfreunde-de.translate.goog/kettenlaenge-rechner/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp

Title: Re: Formula for the length of a chain (?)
Post by: Rajmundx on February 24, 2026, 08:31:06 AM

Quote from: SirBikealot on February 24, 2026, 08:17:24 AM

i used this site for my 54-32 and went with 110 links on a 410mm chainstay.
https://www-bergfreunde-de.translate.goog/kettenlaenge-rechner/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp

Thank you for this website! With my crankset and cassette 108 links will be okay. We will see.. :)

Title: Re: Formula for the length of a chain (?)
Post by: s3si1u on February 25, 2026, 02:32:03 AM

This has worked well for me: https://www.omnicalculator.com/sports/chain-length

Title: Re: Formula for the length of a chain (?)
Post by: SirBikealot on February 25, 2026, 05:20:28 AM

Quote from: Rajmundx on February 24, 2026, 08:31:06 AM

Thank you for this website! With my crankset and cassette 108 links will be okay. We will see.. :)

just in case you missed the bottom line. If you have 11 tooth pulley wheels you need to ad two links to your chain.

Title: Re: Formula for the length of a chain (?)
Post by: NB87 on February 25, 2026, 09:37:09 AM

I always decide chain length the other way around: Put it on small / small and shorten it so in that position it has a bit of tension. Then shift to big/big to check how the chain is in that position.
Especially important to check this when you've specced the cassette or chainrings outside of recommended values. (for instance 11-40 cassette on a 12sp ultegra mech)

Title: Re: Formula for the length of a chain (?)
Post by: alfiomotrambo on February 25, 2026, 10:01:36 AM

Usually i follow the shimano instruction https://bike.shimano.com/stories/article/determine-chain-length.html or bettershifting https://bettershifting.com/installation-guide/installing-a-new-chain-length-and-direction/

Quote

Without routing the chain through the rear derailleur, set the chain on the largest chainring and the largest sprocket.

Have the two chain ends meet at the large chainring, and then add two or three links, depending on the zero point