Before you cut anything
Chains are sold at a standard length that is usually longer than most bikes need, so shortening a new chain is routine. Shortening is also sometimes needed after a stiff or damaged section is removed. Two cautions first:
- Do not shorten a chain to fix slack caused by wear. A worn chain should be replaced. Shortening only makes sense if the chain is too long.
- Check the chain type. Modern chains from different makers use different joining systems, and some need a particular connecting pin or quick link. Check your chain’s instructions.
What you need
- A chain tool (also called a chain breaker), or a multi-tool with one built in.
- A quick link (master link) or connecting pin that is rated for your chain’s speed count.
- Quick link pliers, which help but are not essential.
- The old chain or your bike’s gearing for sizing.
If you do not have a chain tool, see removing a bike chain without a chain tool for what is possible, and the risks.
Find the right length
The common method for a bike with a rear derailleur:
- Put the chain on the largest chainring and the largest rear cog, bypassing the rear derailleur.
- Pull the chain snug and add one full link (an inner link plus an outer link, which is a length of about an inch) as a common rule of thumb.
- Remove everything beyond that point.
Bikes with full-suspension frames or unusual gearing may have different recommendations from the frame or derailleur maker, so check those if relevant.
You can also match the length of an old chain if it was the right length and not worn. Laying the new chain next to the old one and counting links is common practice, though a stretched old chain will be slightly longer than its link count suggests, so compare by link count rather than overall length.
For a single-speed bike, the chain is sized to the two sprockets with enough slack to allow adjustment; see tightening a single speed bike chain.
Break the chain
- Choose the link at which to cut. Many chains end with an outer link on one side and an inner link on the other; the chain must join an inner link to an outer link. Check that the ends you join are compatible.
- Place the link in the chain tool, with the pin aligned to the tool’s driving pin.
- Turn the handle slowly. Push the pin out far enough to separate the chain.
With a standard pin, avoid pushing the pin all the way out unless you will use a new connecting pin or quick link. Pushing a pin all the way out from some chains makes it difficult to re-insert, and some makers recommend never reusing a pin.
Rejoin the chain
- Quick link: Insert half of the link through each end, bring them together, and pull the chain so it locks. Pulling under tension, such as by pressing on a pedal with the brake on, seats it. Check that it is fully seated before riding. Some quick links are intended for one use; check your maker’s instructions.
- Connecting pin: Use the pin made for your chain, and push it through with the chain tool as directed. Some systems have a pin that is snapped off after fitting.
A link that has been pushed together may be stiff; flex it sideways by hand until it moves freely. Stiff links can cause skipping, as covered in bike chain slipping under hard pedaling.
Check your work
- Shift through the whole range with the rear wheel lifted and the cranks turning.
- Confirm that the chain does not bind in the big-big combination, and that the derailleur still has some spring left in the small-small combination.
- Look closely at the join for twisting or gaps.
If shifting is poor afterward, the chain may be a bit too short or too long, or the join may be stiff.
Common mistakes
- Cutting before checking length.
- Joining two outer ends or two inner ends.
- Using a quick link that does not match the chain’s speed count.
- Reusing a pin that the maker says to replace.
- Forgetting to check that the join sits correctly.
Frequently asked questions
How do I tighten the chain on my bicycle?
Shortening and tightening are different. If your bike has horizontal dropouts, see how to tighten a bike chain.
How much does it cost?
Many shops charge a small labor fee for resizing a chain, plus the price of any quick link. Prices vary.
How do I break a chain link?
Use a chain tool, turning slowly so the pin pushes out in a straight line. Stop once the link separates.