How do I know my bike chain size?


It’s time for the annual maintenance of your bike. You decided to take care of the tune-up by yourself but you don’t really know what is the right size, how to change the chain on your bike, etc. 

How do I know my bike chain size? The width of your chain depends on the rest of your drivetrain. Chains for drivetrains with 5, 6, 7 or 8 speeds at the rear are all the same. Above 8 speeds however, and you must match a compatible chain to your drivetrain.

If you want to find out more about the size and brand you need for your drivetrain, then keep on reading!

Chain width:

Indexed shifting requires specific, discreet gaps between the cogs on the cassette so that the shifters can move the derailleur the exact distance needed to position the chain on the next cogs. 

This also requires a chain of a specific width that will fit on and between the cogs of the cassette. As drivetrains with more speeds at the rear were developed, the cogs and the space between them became more and more narrow to squeeze between the dropouts of the bike frame. 

Although it is not important to know what the actual dimensions of a chain is for multi-speed bikes, it is important to know what chain you will need.

It’s time to change the chain on your bike but you aren’t really sure what size and brand you need.

6/7/8 speed chain:

The width of your chain depends on the rest of your drivetrain. Although exact dimensions are not important for multi-speed bikes, it is important to know that chains for drivetrains with 5, 6, 7 or 8 speeds at the rear are all the same. 

Shimano, SRAM and KMC all make appropriate chains, such as the HG40, PC 830 and Z8 respectively. Although Shimano and SRAM both recommend using their own chains on their drivetrains, in practice it makes little to no difference with 8 speed and lower drivetrains. 

My Shimano Claris equipped gravel bike shifts perfectly with a KMC chain installed. (Note: the KMC Z7 claims to not be 8 speed compatible. I have used the Z7 on plenty of 8 speed drivetrains and it works flawlessly).

9 speeds and up:

Above 8 speeds however, and you must match a compatible chain to your drivetrain. 9 through 13 speed drivetrains all have different widths of cogs and gaps between them on the cassette, so a 9 speed drivetrain must have a 9 speed chain and so on. 

(Note that Shimano actually makes both road and mountain-bike 10 speed chains which they claim are not interchangeable). 

Mixing brands:

With lower speed count drivetrains, chain manufacturer tends to not be important. If you find that you have poor shifting and a mismatched chain it can be worth trying to install a matching one, but is unlikely to be the source of the problem. 

However, with higher speed drivetrains, particularly the latest 12 speed mountain bike drivetrains from Shimano and SRAM, chain mismatching is more problematic. 

In general, with higher-end components it is best to use a matching chain for the best performance. Personally, I have not found any issue with mismatched chains on 11 speed and lower drivetrains yet.

Installing a new chain:

To replace a chain, you will need:

  • A compatible chain tool
  • Master Link Pliers (If using a master link)
  • Rubber Gloves (Recommended as handling chains is very messy)

Installing a new chain is very simple. 

First you must remove your old chain. 

If your chain has a master link (two half-links that come together to join two ends of a chain, they will stand out from the other chain links), a pair of Master Link Pliers such as the Park Tool MLP-1.2 will easily pull the link apart. If you do not have a master link then split the chain by pushing out a rivet with your chain tool. 

Do not throw the chain out yet, if it is correctly sized it can be used to measure your new chain. All chains come with extra links, and you must use your chain tool to shorten it. Using the old chain, you can line them up side by side and cut to the same length. 

If your old chain is not the correct length, or otherwise not available, you can size a chain with the following procedure (in most cases):

  1. wrap the chain around the largest cog in the rear and the largest chainring in the front, and bypass both derailleurs;
  2. while holding one end against the teeth of the largest chainring, pull the other end of the chain and wrap it around the largest cog on the cassette or freewheel;
  3. line up the end of the chain against an opposite link (inner and outer links), and then
  • add two rivets of chain length.
  1. Using a chain tool, break the chain at this rivet and attach using a connecting pin or connecting link. (source)

It is important to note that when a chain is replaced, it is not uncommon to experience “skipping”, where the chain suddenly pulls forwards as it jumps over the teeth of the cassette or freewheel. This is especially common if a chain has been used well past .75mm of wear (measured with a chain checker). 

This happens because as the chain wears out it will wear a matching profile into the cogs of the cassette and freewheel. This happens more commonly in the smaller cogs since they have fewer teeth that engage against the chain at once. 

When a new chain is installed, it may not mesh nicely with the profile worn in from the old chain and skip. When this happens, cassette or freewheel replacement is necessary. 

When replacing a cassette or freewheel, it is best to match the size of the current one so that the chain will still fit. Otherwise you may have to add or remove links.

Are expensive chains worth the cost?

In general, more expensive chains will offer more durability, more striking cosmetics or marginal gains, usually in terms of weight. 

Some chains from KMC claim to have rust proofing, others claim to be lighter or more durable, and others are simply nicer looking, with gold plating or other colouring. Many higher end chains will save weight with hallow rivets. 

Usually a more expensive chain will not shift better, so these chains are only worth the cost if you value the changes they offer.

Can a bike chain be put on backwards?:

Some chains can be put on backwards. When you purchase a new chain, the documentation included will specify if it is asymmetrical. 

If a chain has printing or logos on one side but not the other, the blank side should be facing towards the bike while the printed side should face outwards.

1/8” vs 3/32” Chains:

On the singlespeed side, there are two types of chains you can choose from, 1/8” wide and 3/32”. These  chain widths match the widths of your front chainring and rear cog. 

A 1/8” chain is slightly wider than a 3/32” chain so it will fit onto a 3/32” drivetrain, but not perfectly, and is not recommended. Doing this increases the chance of the chain falling off the drivetrain and causing a crash in the worst case. 

Although both chains are very durable, 1/8” chains are thicker and stronger, so they are used by professional singlespeed sprinters to reduce the chance of a chain snap. 

Endurance riders tend to use 3/32” chains for the weight savings. For the average person, there is practically no difference between the two. However, 3/32” chains are actually the same width as 6/7/8 speed chains. 

Many 3/32” singlespeed bikes actually come with normal 8 speed chains installed from the factory. Because of this, 3/32 might have an edge over 1/8” in terms of chain availability. (source)

Conclusion

Conclusion

I hope you found the answers you were looking for and now you can take care of the annual tune-up and change the chain on your bike!

Happy riding!

Ethan Bowering

I am an Electrical Engineering and Computing Technology student attending uOttawa in Ottawa, Ontario. When I'm not studying, I'm fixing and riding bicycles! I have been the head technician of a bike shop, volunteer technician at a bike coop and have run a successful bike repair business from home. From road, to mountain to gravel, I love it all!

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