Knowing how to fit a bike chain is an essential skill for any home mechanic. Chains are one of the consumable parts of your drivetrain and will stretch and wear with use, so you will need to replace it sooner or later.
The steps below are the same whether you ride a mountain bike or a road bike.
How to replace your worn out chain
What you need
- Chain splitter tool (aka: chain breaker)
- Chain checker tool
- Piece of broken spoke
- Quick link pliers
What to do
There are a few exceptions, but most chains from the major manufacturers are compatible with each other's drivetrain components. However, you will need to match the speed of your drivetrain with the speed of your chain — for example a 9-speed drivetrain will require a 9-speed chain.
Step 1: Remove the old chain
Using the chain splitter, push one of the pins out of the lower stretch of chain or undo the quick link if one is installed. Once you've extracted the pin, carefully remove the chain from the bike.
Step 2: Fit the new chain
Shift the rear derailleur into the biggest cog and the front to the biggest chainring. Release the clutch mechanism on your rear derailleur if you have one.
Thread the end of the chain through the front derailleur and turn the cranks so there are a few inches dangling below. Place the other end inside the seatstay and lay it over the cassette. Pull down on the rear derailleur.
Thread the chain over the top of the upper jockey wheel, then behind the tab in the derailleur cage arm, then over the lower jockey wheel and finally through the lower tab. Gently release the derailleur.
Step 3: Size the chain
You need to make sure the chain will operate in any gear, without causing damage to the bike.
To do this, the chain needs to be fitted to the two largest rings, front and rear, although you should never ride in this gear.
With the chain in place, pull the two ends towards each other and measure which one to split by holding them in place. This is where the broken spoke comes in handy.
When you're sure you have the right length, and there's still some movement in the derailleur arm, split the chain using the chain tool.
You can now shift the gears to the smallest cogs by manually moving the chain.
Note: For full suspension mountain bikes be sure to check that the length of chain needed doesn't change as your suspension is compressed. For this, measure the distance from the centre of the crank to the centre of the rear axle. Now release the air (or remove the spring) from the rear shock and take this measurement again. Size the chain in relation to the longest measuring position.
Step 4: Join the chain
For Shimano chains, take the two ends and insert a joining pin using the chain tool. When the pin is in place you can snap off the end with pliers.
For SRAM or KMC chains, take the two ends of the chain and insert the connector links by hand. You can now snap the plates together and the chain will be joined. Special pliers can be used for this, but another way is to pedal the connector link through until it is sitting above the chainstay. Now grab the rear wheel to stop it from spinning and apply pressure to the pedals until the link is fully seated.
Once the chain is connected, you should run your bike through a full range of gears to make sure it's working correctly.
How to care for your chain
The best way to prolong the life of a chain is to clean and lube it regularly. Clean the chain in situ using a chain cleaner, then lube each roller individually, keeping the lube away from the outside of the chain. Try to avoid the temptation to run the chain backwards and apply lube in a hurry — it’s wasteful and can overload the links. When you've finished, wipe off any excess lube with a cloth.
When cleaning the chain, try to avoid driving any degreaser or cleaning products into your bottom bracket or freehub body as this can strip the grease from these parts, causing all sorts of problems.
Lastly, always wipe down and relube the chain after wet rides to avoid it rusting and seizing up.
How to measure a chain for wear
As the chain wears, it deforms the sprocket teeth, which in turn leads to mis-shifting or skipping. You can buy special tools to detect for a worn chain.
Alternatively, you can measure 12 complete links and if this section of the chain measures 308mm or longer, your chain is worn out and should be replaced along with the cassette. For comparison, a new chain should measure exactly 304.8mm across 12 links.
Chain tools and wear checkers
There are a huge variety of chain tools available. For the home toolbox a big tool makes easy work of breaking and joining a chain. The Park CT-3.2 is a firm favourite, but the smaller CT-5 packs a big punch for its size and is small enough to lug around.
You can detect for a worn chain using a ruler as we’ve mentioned above, but chain wear tools are a convenient way to make regular checks.