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Recently, I helped a friend install a new chain on her road bike, and for the first time read the instructions for installing one. It seems to claim that there's a forward direction, and that it actually makes a difference.

Does anyone know if that's actually true? My LBS (which I love dearly) just replaced my chain, and I thought it was installed it backwards. The new chain, if it makes a difference, is a Dura-Ace, 10 speed, CN-7801.

Does it matter? Do I care enough to reinstall it?

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Interesting. Shimano techdocs: "In order to obtain good gear shifting performance, the CN-7900 has a forward side and a reverse side, and the sides are marked so that the CN-7900 will face the correct way when installed. The proper design performance will be obtained when the CN-7900 is installed so that it faces the correct way. If it is installed so that it faces the opposite way, the chain may come off and the bicycle may fall over and serious injury may occur as a result." – lantius Jun 15 '11 at 1:50
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That said, I have no idea what that means in practice, or what asymmetries are in the design to give it an orientation. – lantius Jun 15 '11 at 1:51
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@lantius: I suspect that the plates on one side are shaped for better up-shifting, and on the other for better down-shifting. If installed the wrong way round I can see that leading to unexpected arrival in a lower gear through the down-side side plates hooking the next cog up. But until you pointed that out the use of an assymetric chain had never occurred to me. I am astonished that you found that link without even a chain name to go off! – Мסž Jun 15 '11 at 4:10
    
i also read that it matter how the chain mates to a narrow wide chainring. +-+-+- ect – hue Jun 26 at 17:32
    
A pricey chain. They should reinstall it according to specs as they are a LBS. That said, I run either 105 or sram PC1130 chains and have noticed that the sram chains are noticeable quieter. I don't worry about direction and the bike shifts great with either chain brand. – B Team Jun 26 at 21:13

This Bicycle Repair Guide says:

One- and three-speed bikes use 1/8-inch wide chain, which use master links. There is one master link per bike chain. These snap on and off easily. There are two types of master links. Two-piece master links are opened by loosening the chain, then gently bending the link toward the outside, so the outer plate of the link is free to be lifted off. Three-piece master links have a clip that slides to one side and then lifts off. When reinstalling three-piece links, install the clip with the open end facing away from the direction of rotation, so that friction between the bike chain and clothing, chainguard, etc, will not accidentally remove it.

It's also covered on Bike Forums, here's one of the answers:

Chain direction matters if the chain is worn. If you remove and soak your chain regularly (which, by the way, is not recommended, regardless of how easy it is to remove the chain), then you won't have a problem regardless of orientation of chain. If you remove a well worn chain and install it in the reverse direction, you'll end up with a mysterious skip in your drivetrain. Reverse your chain to see if that's the cause.

There are two exceptions - if the chain has an "inside", i.e. points to the cogs, and "outside", i.e. never contacts cogs, except the pulley of the rear derailleur. If you have such a chain, you'll need to make sure that the inside is inside. You can still reverse its direction though, unless it is also directional, i.e there is a left and a right (the second exception).

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I found that the bad way. And am left with skipping now. Figured out that the chain is probably too worn, and that I probably damaged 'link' while trying to open it. – Daniel Mošmondor Oct 27 '15 at 21:38
up vote 4 down vote accepted

Turns out that while some chains are directional (like the CN-7900 @lantius mentioned), this one is not. So while I'm not sure how much it matters for other chains, in my case, I clearly don't care :)

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Directional are only some high-end chains for example XTR. This can be determined by inspecting the chain. If it is blank on one side, but has company logos and chain number on the other, it is probably directional and the side with the writings need to be facing outword i.e. towards you while installing it. – Vorac Aug 19 '14 at 7:42

Many bicycle chains use different platings for the inner and outer links. Inner links are typically plated with a nickel/Teflon surface. Outer links will only get a nickel plating. The extra Teflon coating helps the inner surface of the chain glide over the cogs on the cassette.

Here is a video of the manufacture process: http://youtube.com/watch?v=h8j5-dC6_x8

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While true, I think this does not answer the question: The inner links and outer links that are treated differently in some chains are the narrow and wide sections of the chain respectively, not the left and right sides. So this aspect doesn't change when reversing the chain. – Emil Jun 26 at 20:24

I know you are supposed to:

  • Resize the chain by from the side that terminates at an inner link, this way when you place the new pin into the chain, the outerlink has never had a pin in it before. There's wear created on outerlinks when you insert and remove a pin as you probably guessed by how much force you need with a chain tool to insert and remove a pin. BTW - lube your pin before inserting it..

  • When installing the outerlink should be forward to the direction of travel of the chain. This is the "forward way" to connect it, the other way is backwards which is what I think you are asking about. If you follow both this rule and the first one I listed you will automatically follow the next rule:

  • Some chains are asymmetrical slightly, this is to improve shifting. If you look on your chain ring, you can see that it has guides for upshifting. The chain will better ride these up while shifting especially when under power.

So, in answer to your question, I think it's to guarantee that you install that chain so that if it is asymmetrical, it will be installed properly. If you don't install it properly, the chain can more easily snag while shifting.

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