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What is a narrow wide chain and what are it's benefits and drawbacks?

Also, is a specific chainring or cassette required?

  • 3
    I think you should roll back that edit. Now there's nothing in the title that indicates you're talking about the drivetrain. At first glance I thought you were talking about saddles. – BSO rider Oct 12 '16 at 15:43
  • It seems someone else already has re-edited. – Mark W Oct 13 '16 at 10:45
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You're probably thinking of narrow-wide chainrings:

enter image description here

Modern chains have inner and outer links. On a conventional chainring, all of the teeth are the same width, and therefore have to be narrow enough to fit into the chain's inner links. This means that there's enough space for the chain to move about a bit from side to side on the chainring, which can cause it to fall off.

Historically this hasn't been much of a problem, since on geared bikes the front derailleur cage tends to stop it from falling off, and on single-speed bikes there's no chain slack or gear changing at the rear to cause chain-drop.

However, when you remove the front derailleur, but keep the rear derailleur (as is becoming common with single-ring setups), dropping the chain becomes more of a problem. This can happen when changing gear on the cassette, or when a bump causes the chain to go slack momentarily.

Narrow-wide chainrings have alternating narrow and wide teeth that fit into the inner and outer links respectively. This makes the chain more secure on the chainring and less likely to fall off.

A narrow-wide ring is only necessary if you have a single chainring at the front and a rear derailleur. They won't work at all if you have more than one chainring at the front, since you won't be able to change gear. You don't need a special cassette, but you might benefit from using a clutched rear derailleur (particularly on a MTB), which prevents the chain from going slack on bumpy terrain.

A well-established alternative to a narrow-wide ring is a chain guide, which behaves somewhat like a front derailleur in keeping the chain from falling off:

enter image description here

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    I am indeed. I've heard the term "narrow wide" thrown around a lot and assumed it referred to a chain type. Thanks for the informative answer. – Mark W Oct 12 '16 at 14:10
  • Nice answer. In that last photo, it looks like the chain guide is mounted on a fixie or single-speed drivetrain — is a guide really necessary on these, since the chain has far-reduced movement along the width of the bike? – Jules Oct 13 '16 at 14:34
  • @Jules No, it's not really necessary, since there's never enough slack in the chain for it to fall off (assuming it's correctly tensioned). I don't think it's a single-speed, though; the chain looks like it's designed for derailleurs. – Will Vousden Oct 13 '16 at 14:54
  • A bit late here, but that's a front derailleur braze-on mount above the chain guide - the white bicycle frame in the bottom picture is definitely designed to be able to use a front derailleur, and I don't know of any bicycles designed for a front derailleur that don't also have a rear derailleur. – Andrew Henle Dec 26 '18 at 23:15
  • There is overlap between "bikes designed for a front derailleur that now aren't using one" and "bikes that are now being used singlespeed" though. But Google says it's a Tern folding bike - the short chainstays on a small wheeled folding bike can make chain dropping more of a problem. ternbicycles.com/ca/gear/471/mainstay-chain-guide – armb Sep 11 at 16:12

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