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My fixed gear bike is going to want a new chain soon, how do I figure out which width I should use?

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1/8 inch -- See Sheldon Brown – Daniel R Hicks Nov 3 '12 at 21:57
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Many of the newer, more mass-produced fixed gear bikes (non track) just use 3/32", so Sheldon doesn't necessarily hold up with this. Since 3/32" is probably easier to find at a vast majority of bike shops, as well as just being a bit more universal they've moved to this sizing. Unless you bought a track bike for use at the track or a higher end "fixie", you're probably using a 3/32" chain. – Tha Riddla Nov 4 '12 at 12:27
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Here's another idea: Get one of the old chains in your used bike parts box and see how well it fits the sprockets. Assuming you've been riding a multi-speed bike of recent origin, the chain will be 3/32", more or less. If it binds on the sprockets you need a 1/8" chain. – Daniel R Hicks Nov 5 '12 at 19:02

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There two sizes of chains that can be used on a fixed wheel bicycle 1/8" and 3/32". It all depends on the width of the teeth on the cog and the chain ring. The most common one is 1/8" as that is what is used on the track and BMX. On bikes that have been converted from gears to fix are more likely to be 3/32". My Son's bike has a 3/32" cog, chain ring and chain.

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Take your bike to a bike shop and they will tell you the size. – Kipper Nov 3 '12 at 22:28
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It's just a chain, lets keep the LBS out of this one okay? – hillsons Nov 4 '12 at 5:21
Sorry hillson, I did not know if you had the equipment or know how to measure the components yourself, thus the LBS advice. – Kipper Nov 4 '12 at 20:08
If you get an 1/8" chain you can run that on either 3/32" or 1/8" rings. So if you can't figure out which size to get, then get 1/8" and it should work fine. – Benzo Nov 5 '12 at 14:56
@kipper's response is maybe not such overkill. I have 4 bikes, one of which is single speed. Three of them are a doddle to source parts for (2xShim, 1xsram). Then there's the single speed.... In all the work I've done on it I have needed to research the sizes of bb, chainring, hub and of course chain. Its a beautiful bike to ride but it has taken more effort in terms of time (i.e. finding stuff out about it) than the other three bikes put together. If it really is "just a chain", why not buy one of each width? – PeteH Nov 5 '12 at 16:23
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Get a pair of calipers and measure the width of both the chainring and the cog. If the width is much larger than 3/32" then use 1/8".

If you don't have calipers, but have a piece of 1/8" chain, then put the chain on the cog and the chainring and see if there is a large visible gap between the plates of the chain and the teeth, if so then can probably use a 3/32" chain, if it's pretty snug you probably need a 1/8" chain.  If you have a 3/32" chain instead, then put it on both cog and chainring, if the teeth fit through the holes in the chain and the chain rests evenly on the cogs, you're probably fine with a 3/32" chain, if it sits unevenly at all, you probably need 1/8".

If you don't have a chain, then you could check for width markings on your chainrings and fixed cog, if they are single speed chainrings they tend to have a width marking on them (to distinguish between 1/8" and 3/32" sizes).

Keep in mind, If either the rear cog or front chainring is larger than the other in width, you need a larger 1/8" chain (which really won't run poorly on a smaller chainring, but a smaller 3/32" chain just won't fit on a 1/8" cog or chainring).

Also, If you're buying a 3/32" chain, you'll probably find that as a 6/7/8 speed chain at most bike shops. You probably don't want to try to use a 9 or 10 speed chain on a single speed bike. 1/8" chains are used exclusively for single speed setups.

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