Your chain is a key element of your bike’s transmission, being the essential link that connects the front part of your drivetrain (the pedals, cranks and chainrings/sprocket) to the rear (cassette/sprocket and rear hub). It’s through the chain that pedal power is converted into forward movement, so it’s essential to buy the right one and to keep it maintained.
Modern bike chains are properly called ‘roller chains’, and consist of short cylindrical rollers held together by side links. The gaps between the rollers mesh with the teeth on a sprocket or chainring, to drive the transmission when turned.
Most bike chains are made of alloy steel for strength but some performance models may feature high-end alloy parts or hollow pins/side plates to save weight.
The type of chain you need will depend on the type of bike you are riding. A number of different chain widths are available, to suit specific bike types such as BMX, or to fit different road and MTB drivetrains (e.g. an 11-speed cassette requires a different chain to a 9-speed one – the chain must be thinner in order to fit into the narrower spaces between the sprockets.
Whatever bike you ride, chain maintenance is key. Chains will wear and stretch over time, and a worn chain will damage the teeth on your chainrings or sprocket. It’s important to keep your chain clean and lubricated to minimise wear, and to regularly check chain length so it can be replaced when necessary.
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When replacing your road or mountain bike chain (see below for tips on how to care for your chain, and when to know it’s time for a new one) you need to get one that matches the number of gears in your drivetrain.
The amount of sprockets on your rear cassette – 9, 10, 11, or even 12 – is crucial. Because the distances between the sprockets vary on different ‘speed’ cassettes (e.g. the gap will be wider on a 9-speed block than on an 11-speed), you need a chain that fits. A chain for an 11-speed transmission will be narrower than one for a 9-speed, etc.
Generally chains and cassettes from different manufacturers will be compatible with each other, although Shimano and SRAM chains will not work very well with Campagnolo cassettes, and vice-versa.
It is also worth noting that some chains (e.g. Shimano) require special rivets to rejoin them once they have been split, and the old rivets cannot be used again. SRAM chains use a special ‘Powerlink ‘that can be split and rejoined without the need for a special chain tool, making them a popular choice even on non-SRAM transmissions.
There is plenty of information in print and online on fitting a new chain and specifically on ensuring it is the correct length (all new chains are longer than necessary and will need to have links removed). It is a straightforward job easily tackled by most home mechanics, but if in doubt, have a professional do it for you.
All chains have a limited lifespan. Every time a link of a chain drops into the valley created between the teeth on a cassette, sprocket or chainring, two metal surfaces rub together. Add in the grinding paste that a transmission attracts and multiply by the hundreds of times this happens every time you turn the pedals, and you have a recipe for wear and tear.
As chains wear out they tend to stretch, eventually starting to skip over the teeth on the sprocket when under load, instead of meshing with them as they should.
Once this starts to happen it is time for a chain replacement (and perhaps a new cassette and chainrings too, if the wear is considerable). However you can act earlier by using a chain measuring device to determine if your chain is beginning to wear – catch it quickly and you only need a new chain.
An alternative, but less accurate, method is to measure the length of 12 links, which on a new chain should be exactly 12”. When 12 links of an old chain measures 12 and 1/8” or less, you can get away with a new chain only. Any more than that however and you are going to have to buy a new cassette and possibly chainrings as well.
Another – less accurate again – way is to measure by sight. Lean the bike against a wall, drive side facing outwards, and ensure your chain is shifted onto the smallest rear sprocket and largest front chainring. Now take the chain between your thumb and forefinger at the 3 o’clock position and pull towards you gently. If the bottom jockey wheel of the rear derailleur moves, it’s time for a new chain. If, however, you can pull the chain far enough to see all or most of the tooth, it’s time for a new cassette and probably new rings too.
There are two types of BMX chain – traditional and half-link.
Traditional chains use the same inner link-outer link configuration as other road and MTB chains – so essentially one link consists of two ‘half-links’, inner and outer. These are the most common types of BMX chains found on all kinds of bikes.
Half-link chains are made from identical links that have a thick and a thin end. At the thick end they are the standard width of the chain (equivalent to the outer link of a traditional chain), and the link then narrows to the thin end, which is the equivalent width of the inner link of a traditional chain. The logic behind the development of half-link chains is that less material needs to be removed in order to shorten them – a half-link rather than two half-links – so more precise adjustment is possible, and riders can get their rear wheel position dialled in to their preference.
The majority of BMX chains – both traditional and half-link – are the standard 1/8” width. Narrower 3/32” chains are available for weight-shaving racers, as are more heavy-duty 3/16” chains, but for most riders the standard is fine.
Chains are sold in standard lengths of 96, 98 or 112 links so you will need to use a chain tool to get it the right size for your drivetrain before installation.