Like it or not, bike chains “stretch” over time. Only by a small amount, but multiply that by the number of times each link passes over your chainrings, cassette and jockey wheels and you’ll quickly wear them out, if you don’t regularly replace your chain. A worn chain ultimately leads to the most common mechanical problem with bikes.
You’ll save money if you replace your chain before it becomes too worn. Normally, you can get through around 3 chains, before you need to replace the cassette. A new chain costs around £12-£15 and a new cassette costs around £20.
Rather than provide you with a “chains wear out after X miles” figure that will be a wild estimate, it’s easier to simply check for yourself.
Using Chain Wear Tool
The best way is to simply use a chain wear tool.
You slot the one side in to a chain link and then drop the other side on to the chain. If it slips in to the slot then it means the chain is worn.
You can also flip it to the 1.0 side to see if the chain is more than 1% worn. At which point you probably also need to replace the cassette.
Pull the Chain
If you really don’t want to spend the money on a chain wear tool, then you can less accurately check by simply pulling the chain.
Start by shifting in to the biggest chainring at the front and smallest cog on the cassette.
Pull the chain at the front of the chainring. If it lifts off the chainring, then your chain is starting to wear. The chain shown in the image above is not worn.
Using a Ruler to Look for Chain Stretch
This should ideally be performed while the chain is still on the bike (I know I failed to do that in the picture above!). The zero mark of your chain should be placed directly above the centre of one of the chain pins. Then you need to count 12 complete links. A complete link would be everything you see in the picture above between the numbers 11 and 12.
The 12th link should line up with the 12 inches mark.
If the centre of the pin is 1/16” or 1/8” past the 12 inches mark, then you probably need a new chain. If it is more than 1/8” past the mark, you’ll have to replace the chain and cassette.
I’ll do a follow on post on replacing a chain. If you’d like to hear about it, then make sure you subscribe to our newsletter by using the form below.
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As seen on The Guardian, BBC and The Independent.