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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
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
@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

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:

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