A chain is one of the most important mechanical elements on any bike. You can ride without gears, without brakes, without a seat and even get home if a pedal breaks, but it’s game over if your chain breaks.
The humble bicycle chain is a relatively simple device that has been refined over time to the piece of craftsmanship it is now. It is controlled by standards that govern how wide it is and how much spacing between pins it can have (12.7mm if you wanted to know). It is made up of multiple pieces that combine to make the whole.
The weakest link
A chain link is made up of an inner plate, outer plate, pin and roller. The inner and outer plates hold everything together while the pin and roller integrate with the cassette and chainring to provide the purchase needed for momentum.
We tend to put a bike chain through a lot. Not only does it have to contend with the wattage we put out, it also has to contend with weather, wear, road dirt and grit. A well maintained chain can last for years or many thousands of miles. A poorly maintained chain could fail at any time.
Any damage to the chain is usually collectively referred to as chain wear.
How to detect chain wear
Usually, chain wear manifests itself in poor shifting. The design of a bike chain is such that it sits deeply between the teeth of your cassette and chainring. This is to avoid slipping which increases pedalling efficiency. As the chain wears, it won’t sit so deeply between those teeth and shifting will be compromised as a result.
You may detect noisier shifts, or sloppier shifts, where changing gear doesn’t feel as slick as it once did. You might also notice the chain not sitting as snugly on the chainring or cassette during maintenance. If you do notice this, it’s time to check the chain.
Chain wear comes in two forms, the stretching of the inner and outer plate and the wearing of the roller. Both can contribute to poor shifting and both will need addressing.
How to check for chain wear
Ideally, you should have a chain checking tool, but otherwise, a reliable ruler or tape measure will work.
If you have a chain checker, it sits inside the rollers and can accurately measure the distance between them. If the tool is loose between the rollers, it can indicate wear. The checker tool should have some numbers on the side to help measure too. Be aware though that some tools measure distance and others measure percentage of stretch. Check what yours is telling you.
Usually, the chain checker will slot comfortably into place on your chain. It should not need forcing in and should not be loose once in.
Using a measuring tape or ruler, measure 12 links and it should equate to 12 inches exactly.
To check for roller wear, try to wiggle the chain from side to side. Be aware though that there is no current standard for lateral movement. Some manufacturer’s chains may move more than others. However, if you notice excessive movement or a lag when shifting, this could be an indicator of a worn chain.
When should you replace your bicycle chain?
You don’t measure chain wear by time or distance. We all ride differently and in different conditions. Someone who rides at a relatively low wattage at a high cadence won’t stretch their chain as much as someone who stomps on their pedals. They will however, wear the rollers out faster than the stomper.
Distance isn’t a measure either as riding style, weather, maintenance and conditions will also influence wear.
The popular measure is chain stretch of up to 0.5% is okay. As soon as it hits 0.5% it is time to change the chain. Also, if you begin to notice movement, sloppy shifts or that the chain is looking tired, change it anyway. For the sake of £20-30, you get a new chain, the confidence it brings, the higher efficiency that comes with it and the knowledge that you have perhaps avoided a mechanical far from home.
Finally, whenever you check your chain, check your cassette too. While some experts change the cassette every time they change a chain, it isn’t always necessary. Check the teeth for wear and act accordingly. I tend to get three chains to every cassette. Your mileage may vary.