Chain Length

I was asked the question today about calculating the correct length of a new chain before fitting. Hope this helps:

Chain Sizing - Largest Cog and Largest Chainring Method
An alternative method for determining chain length for new chains is to use the largest size sprockets on the bike. It is easiest to size the chain without threading it through the derailleur.

1) Remove the old chain.
2) Shift the front derailleur over the largest chainring, and the rear derailleur on the smallest cog.
3) Thread the new chain through the front derailleur. It is not necessary to thread the chain through the rear derailleur at this point. Simply wrap the chain around the largest front chainring and around the largest rear cog. 4) Pull the chain tight, and note the closest rivet where the two could be joined. Keep in mind a chain can only be joined by mating inner and outer plates.
5) From the closet rivet, lengthen the chain by counting over an additional two rivets (two links), which is a distance of one-inch.
6) Cut the chain at this point.

Remove the chain from the bike and thread it through both derailleurs and join the ends.
MASTERLINK NOTE: If the bike chain uses a "master link", it is necessary to account for the link. Install one-half of the master link on one side of the chain. Size the chain by cutting the other end of the chain

Thanks for the advice today N@th.


Top Tip: When trying to link the chain together use a cable ties to hold the chain in place,otherwise you need half a dozen pairs of hands.

Alternatively:

1) Remove the old chain.
2) Measure new chain against old chain

yeah yeah,some muppet threw the old chain away before getting the new one......wasn't me honest guv!!!!

I know another muppet who sized his chain up by measuring it against the old one only to find it didn't fit..... because he'd also changed the rear cassette and front chainrings to ones with different ratios... doh!

Said muppet was me.

Always found the "traditional" method as described by Nath as a bit of a pain, so always use the "old chain" method which has always worked well for me.

Am I being a bit thick here? But dont you usually change your chain because the old one has worn and stretched? So why measure the new chain against the old one? Each time you follow this process it must get longer!

Chains don't stretch much as such. The rollers where they engage the teeth wear so that gap between the rollers increases so it looks like its stretched.
No sure if Ive explained it properly but I know what I mean

When you are measuring you are really ensuring the new chain has has the same numbers of links as the old one. You are not actually measuring it's metric/imperial length.

Craig wrote:When you are measuring you are really ensuring the new chain has has the same numbers of links as the old one. You are not actually measuring it's metric/imperial length.

Thanks Graig, that makes a lot more sense!