How to tell what length of chain to get?

I am replacing the chain on my road bike soon. How do I know how many links to get? Does it have to exactly 114 or 116. Or is it not a big deal?

I ordered a 116 link chain. Will I need to shorten it?

Thank you.

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3 Answers

If your old chain was 114 links (assuming it was the right size to begin with) then it's a good idea to take a couple of links out of it. It'll still work with two extra links but shifting may not be optimal and the chain will fall off more easily. Keep in mind that one chain link is composed of an inner and outer link, so a link is actually two pieces with a hinge in the center. This means that to remove two links, you'll actually remove four pieces of chain with three hinge points.

If the old chain was 116 links and you're trying to replace it with a 114 link chain, you'll run into problems. A chain that is too short can jam when shifting and puts puts too much strain on your rear derailleur.

To determine the correct length, wrap your chain around largest chain ring in the front and the largest rear sprocket, without running it through the derailleurs. Make sure that the chain is long enough for one full link (again, inner and outer) to overlap and you'll probably be spot on.

You can read more about it here: http://sheldonbrown.com/derailer-adjustment.html#chain

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Last two paragraphs "rule". Actually, most chains already come with extra-length, so shortening is almost always necessary. The procedure to measure the chain (instead of some other calculation), is what settles the correct length, in the end. – heltonbiker Jul 3 '12 at 16:26

As always, Sheldon knows best.

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The above link is a great explanation...you may want to go to your local bike shop and ask them to talk you through it. Most (even some of the big ones) will do this for free, especially if you buy the chain there...bike mechanics usually like to spread the know-how. Worth keeping in mind that it's relatively easy to shorten a chain that is too long, but making one longer...not so much. – Ken Hiatt Jul 2 '12 at 17:38
Lengthening a chain isn't that hard, if you have the left-over piece. It's difficult to use a chain repair tool on the road, in the driving rain, but fairly easy sitting at a workbench with the chain stretched out in front of you. – Daniel R Hicks Jul 2 '12 at 18:35

A standard replacement chain is always several inches longer than needed for a standard non-recumbent, non-tandem bike. What I generally do is hang both from a wire and match up the links (the old chain will be "stretched", so you can't simply match by length). Then I "break" the new chain at the location (number of links) that matches the old.

Skilled mechanics can simply stretch the chain around the big rings front and rear, put their finger on the link that meets the other end, and break it there, but I'd rather be sure that my new chain matches the old exactly (if the old performed well).

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Isn't the "stretch" just the wearing of the joint between links? So each link should still be the same length, yeah? Which means hanging it from a wire should work just fine. – Sponge Bob Jul 2 '12 at 18:36
@KeeganMcCarthy, the stretch is indeed just the wearing of the joint, and though each individual link remains the same length, a chain of them is longer. In other words, a stretched chain with 100 links will be longer than a new chain with 100 links. – amcnabb Jul 2 '12 at 21:07
Specifically, if you the 1% on the gauge 'just' drops, and you started with 100 links, your old chain will be one link longer than your new chain. (In practice, most of the chains I fit onto backs run a few more than 100 links...but I find this visualization good when I start drawing pictures of what's actually happening when the chain "stretches"). – Ken Hiatt Jul 3 '12 at 0:11
Yeah, when I replace a chain it's usually at around 0.8% worn, so the old chain (which is a hair over 50 inches/100 links) is about one half inch longer than the new chain should be. And a link is one half inch, so the old chain will appear to be one link longer than the new one should be. But it's the same number of links. – Daniel R Hicks Jul 3 '12 at 0:26