How can I tell which size chain my bike uses?

Question

After learning how to break a chain and reattach it, and also how to add and remove a master link, I find that I can now do much more in the way of maintenance at home. I'll no longer need to bring my bikes into the shop simply for a new chain... if I can only figure out how to identify what size chain I'll need to order.

Is there a simple way of telling what size and type of chain I'll need to order to replace the chain on a bike? Do I measure the chain links? Count links? Count gears on the cogs?

If it helps, some of my bikes' drivetrains have internal hubs, some have derailer gears.

Answer 1

If you are using a bike with a derailleur the number of cogs on the rear hub will determine the chain size you will need. They are always 3/32" chains.

You can get a 5/6/7-speed, 8-speed, 9-speed, or 10-speed chains.

If you can't find a chain that matches your cluster pick a chain for a larger number, for example if you have an eight-cog cluster you can use a eight, nine or ten-speed chain, but you shouldn't use a 6 or 7-speed chain.

Internally geared hubs will have their own specification for the size chain they require, and single-speed, fixie, BMX bikes, and probably some older bikes use 1/8" chains.

Answer 2

The correct length of a chain is irrelevant at purchase since they all come at a set length. (Usually 114 1/2" links, sometimes 120 1/2" links). In special cases, like tandems and recumbents, you may need to join 2 chains to have enough length.

Sizing a chain to length for a particular bike is a set process. It does vary a bit.

In the case of an IGH bike, which for this purpose is essentially a single speed, set the rear wheel in the dropouts of your frame, leaving the axle nuts or quick release loose, with the wheel all the way forward in the dropout. (Bikes with concentric bottom brackets should be in the most relaxed position available.)

Wrap the uncut chain around both the chainring and the rear cog. Find the place where the chain meets with no slack. Mark that link, being careful to make sure you pay attention to the outer plates, and have a set of inner plates to pin through them. Add 2 links to this marked length, to give yourself slack to adjust the chain tension, and cut the chain. Rivet the chain together using the link, pin or rivet which the brand of chain requires.

Derailleur geared bikes use a similar method, except that you wrap the chain around the large front chainring, and the large rear cog without going through the derailleur. Adding the 2 links here gives the appropriate amount of slack for the derailleur to operate.

And that's how you do it. There are diagrams on the rear derailleur manual pages, which I'll add when I'm not on the mobile site.

Answer 3

The length and number of links doesn't matter - as all chains are sold too long and you'll need to remove some links to make it the correct length for your bike.

The width is critical. You need to get one that suits the number of gears on your cassette/cluster/rear sprocket (those are all terms for the same thing - the gears on the back wheel of your bike). Count the number of gears, not the teeth on the gears (that's irrelevant). You will probably have either 1 (single speed), 7,8,9,10, or 11 (probably not 11 - those are very expensive and since you're asking this question I'm guessing you don't have 11). When you buy a new chain, tell the bike store guy (BSG) that you need a chain for X speed where X is the number of gears. If you buy online, the description of the item will specify this number.

The size of the links (in mm or inches) is irrelevant if you get the number of gears right.

The brand will probably be printed on the chain links. It is probably Shimano, SRAM or possibly Campagnolo. Although some are compatible, I'd recommend you get the same brand as your rear cassette.

The "type" of chain is printed on each link = HG-70 or something like that. I recommend that until you really know what you're doing, just buy the same one that came off the old bike.

Answer 4

The 1/8" or 3/32" refers to the internal width of the chain, i.e. the width of the rollers. Other sizes do exist, but are rare: http://www.sheldonbrown.com/gloss_ch.html If you look at a 1/8" and 3/32" chain side by side, it's fairly clear which is which.

Chains for derailleur use have thinner sideplates and therefore a smaller external size for increasing number of sprockets. So in principle you can measure the outside width and work it out that way, but in practice its much easier just to know how many gears are on the bike you want to use it with.

It's not entirely true that you can always use a narrower chain designed for more sprockets if you don't have the right size available - if you use a 9-speed chain with a chainset or sprockets designed for 7-speed chain, you might find that shifting is poor because the little shaped ramps designed to catch on the chain and help lift it onto a bigger gear don't catch the smaller plates properly, or even that the narrower chain can jam into a gap between sprockets where the correct chain wouldn't fit. http://sheldonbrown.com/speeds.html#chains