Short answer: measure your chain with a chain checker, buy a replacement that matches the number of gears on your back wheel, break the old chain with a chain tool (or open its quick link), cut the new one to the same length, thread it through the derailleurs and join it with a new quick link or connecting pin. With the right tools it is one of the easier home jobs on a commuter bike, and doing it on time saves your cassette.
This guide covers bikes with derailleur gears, which is most commuter hybrids, road and gravel bikes. If yours has a single speed or a hub gear, skip to the section on those bikes first.
When does a chain need replacing?
Chains don’t really stretch. The pins and rollers wear, the gaps between them grow, and the chain gets slightly longer. A long chain no longer sits properly on the teeth of your sprockets and chainrings, so it starts wearing them into the wrong shape. Leave it too long and a new chain will skip on the old cassette, which turns a cheap repair into a dearer one.
Park Tool’s guide on when to replace a chain gives these general thresholds:
| Drivetrain | Replace at |
|---|---|
| 11-speed cassette or more | 0.5% wear |
| 10-speed or fewer | 0.75% wear |
| Single-speed | 1.0% wear |
Park Tool adds that every drivetrain manufacturer has its own specification, so if your groupset’s manual gives a different figure, use that.
Checking with a chain checker
A chain checker is a small gauge that drops into the chain at a set wear level. Park Tool’s CC-3.2, for example, has a 0.5% end and a 0.75% end. Push the tip in at the 0.5% end first: if it doesn’t drop fully into the chain, you’re below 0.5%. If it does, check the 0.75% end. Hold a little tension on the chain while you do it, so you’re measuring the real gap and not slack.
Checking with a ruler
No gauge? Use a steel ruler marked in inches, because chains are built to a half-inch pitch. Line up one rivet with the zero mark, then count 24 more rivets. On a new chain, that last rivet sits on the 12-inch mark. Park Tool says that if it’s off by more than 1/16 inch, the chain is worn enough to replace. It describes this as a ballpark method, so treat a borderline reading as a reason to buy a gauge or ask a shop.
Signs on the road also help: a chain that jumps when you push hard, or gears that won’t settle after you’ve adjusted them properly, are worth a measurement. Squeaks are usually a lube problem, not wear; our chain cleaning and lubing guide deals with those.
Buying the right replacement chain
The key number is how many sprockets you have on the back wheel. Count them, or look for the speed printed on your gear shifter or derailleur.
- 5 to 8 speeds share a common chain width, so an 8-speed chain fits a 6-, 7- or 8-speed bike, according to BikeGremlin’s chain compatibility guide.
- 9 speeds and above get narrower with each extra sprocket. Match the chain to the cassette: a 10-speed bike wants a 10-speed chain. The same guide warns that a wider chain can get stuck between narrower sprockets, while going one step narrower usually works but tends to cost more and wear faster.
- Brand: most chains work across brands at the same speed, but check the description for your groupset. Some chains are directional and must face a particular way (more on that below).
New chains are often sold longer than a typical bike needs, so expect to cut yours to size. Many come with a quick link or a connecting pin in the box; check before you order a separate one. For prices, check current prices at your local bike shop or online.
Tools you’ll need
- A chain tool (also called a chain breaker) that suits your chain’s speed
- Master link pliers, if your chain uses a quick link (you can manage without, but they make it easier)
- A chain checker or steel ruler
- Rags, gloves and chain lube
Step 1: Remove the old chain
Shift into the smallest sprocket at the back. Taking the rear wheel out reduces the tension, but it isn’t essential.
If the chain has a quick link (a link that looks slightly different from the rest, often a different colour), find it on the lower run of chain and squeeze it open with master link pliers. If you’re throwing the chain away anyway, Park Tool notes you can ignore the quick link and simply break the chain a few links along with your chain tool.
If there’s no quick link, pick a rivet several links away from any connecting pin that’s already there. Set the chain in the tool, keep the driving pin straight and centred on the rivet, and wind it in until the rivet pushes out and the chain separates. Park Tool’s chain replacement guide describes feeling two points of resistance as the rivet passes through each outer plate. Then pull the chain off the bike.
Step 2: Size the new chain
If your old chain was the right length, the simplest method is to lay old and new side by side and match them rivet by rivet. Park Tool warns that the old chain has lengthened through wear, so line them up link for link rather than measuring end to end. If your chain uses a quick link, include it in the comparison.
If you’re not sure the old one was right, use Park Tool’s big-big method for cassettes with a largest sprocket of 36 teeth or fewer:
- Wrap the new chain around the largest chainring at the front and the largest sprocket at the back, going through the front derailleur but not through the rear derailleur.
- Find the closest point where the two ends could join, with an inner plate meeting an outer plate.
- Add two more rivets (one inch) and that’s your cut point. If you’re using a quick link, fit half of it while you measure to account for its length.
Bikes with very large rear sprockets (42 teeth or more on a single-ring drivetrain) and full-suspension bikes need a different method; follow the Park Tool guide or your derailleur maker’s instructions for those.
Cut the new chain with the chain tool. Remember which end needs to be inner plates and which outer: a quick link joins two inner-plate ends, while a connecting pin joins an inner-plate end to an outer-plate end.
Step 3: Thread the chain through the bike
Check whether the chain is directional. Park Tool’s advice is that on directional chains, any logos or printed letters should face out towards you on the drive side. Some quick links also carry an arrow showing the direction of travel.
Start at the rear derailleur. Feed the chain through the cage, making sure it passes the correct side of any tabs inside the cage; a chain routed outside a tab will rub or fall off. Bring it over the smallest sprocket, through the front derailleur cage and onto the smallest chainring. Leaving it on the small ring gives you slack to work with while you join the ends.
Step 4: Join the chain
With a quick link: fit one half into each end, hook them together, then pull the link into place with master link pliers. Without pliers, Park Tool suggests turning the link to the top run of chain, holding the rear brake on and pressing down on the pedal so the chain tension snaps it shut.
Many quick links are meant to be used once. SRAM’s 10- and 11-speed PowerLocks, for example, should not be reused: BikeRadar reports SRAM’s explanation that the ridge joining the two plates can be damaged when you open the link. Other brands sell reusable links. Follow the instructions in the pack, and fit a new link if you’re unsure.
With a connecting pin: use the pin made for your chain’s brand and speed. Park Tool says to lubricate it and push it in from the inside of the bike towards you, so any burr ends up facing away from the cassette. Drive it in with the chain tool until it sits level with the rivets either side, then snap off the guide tip. Campagnolo’s 11-, 12- and 13-speed chains need an extra peening step after this; follow their instructions.
Step 5: Check your work
- Look for a stiff link. Turn the pedals backwards slowly and watch the chain run through the rear derailleur. A link that kinks or jumps is stiff; flex it gently side to side to free it.
- Shift through every gear. Run through all the sprockets on each chainring, in the workstand or on a quiet road.
- Test under load. Ride a short way and push hard in the gears you use most. If the new chain skips, Park Tool notes it may be a sign of a worn cassette or freewheel.
- Lube it. Keep the new chain on your usual cleaning and lubing routine from the start. Our clean and lube guide explains wet versus dry lube for British conditions.
Single-speed and hub-gear bikes
Bikes without derailleurs work differently. Sheldon Brown’s chain pages describe the wider 1/8-inch chain as the traditional choice for single-speeds, three-speeds and other bikes without derailleurs, while 3/32-inch is the derailleur width. Check what your sprocket is designed for before you buy.
Chain tension on these bikes is usually set by sliding the rear wheel in the frame or by a separate tensioner, not by a derailleur, so the sizing method above doesn’t apply. Some hub-gear wheels also need the gear cable disconnecting before the wheel comes out. If you haven’t done it before, follow the bike maker’s manual or ask a shop.
When to let a shop do it
Replacing a chain is a reasonable first job for home maintenance, but a shop is the sensible choice if the new chain skips and you suspect a worn cassette, if you have a hub gear or full suspension, or if you’d rather not buy a chain tool for a job you’ll do once in a while. If you go down that route, our guide to the Halfords bike service explains what the different levels include. For the routine checks that keep a chain going longer between replacements, see our basic bike maintenance guide.
FAQ
How do I know when my bike chain needs replacing?
Measure it rather than waiting for it to slip. Park Tool’s general guideline is to replace at 0.5% elongation on 11-speed and above, 0.75% on 10-speed and below, and 1.0% on single-speed, though your drivetrain maker’s own figure comes first. A chain checker gives the answer in seconds; a ruler gives a rough reading.
Can I fit any chain to my bike?
No. Match the chain to the number of sprockets on your cassette. Chains for 9-speed and above get narrower with each extra sprocket, so a wider chain can catch between the cogs. Single-speed and hub-gear bikes traditionally use a wider 1/8-inch chain.
Can I reuse a quick link?
Often not. SRAM says its 10- and 11-speed PowerLock links should not be reused, because the part that holds the two plates together can be damaged when you open it. Some brands sell reusable links. Follow the instructions in the pack, and if in doubt, fit a new link.
Should I replace the cassette at the same time?
Only if it needs it. If the new chain skips under load after fitting, Park Tool notes this may indicate a worn cassette or freewheel. Replacing the chain before it wears too far helps the cassette last longer.
