First, work out what kind of bike you have
You can only tighten a chain in the way most guides describe if the rear wheel can move in the frame. That depends on the bike.
- Single-speed, fixed-gear and many coaster brake bikes have horizontal dropouts (slots) that let you slide the rear wheel back to take up slack. This is what “tightening” normally means. The full procedure is in tightening a single speed bike chain.
- Bikes with a rear derailleur have a spring-loaded derailleur that keeps the chain taut. You do not tighten the chain by moving the wheel. A sagging chain here usually means the chain is worn or the wrong length.
- Internal hub gear bikes may use horizontal dropouts, a chain tensioner or an eccentric bottom bracket. Check how your bike is built before loosening anything.
How to check chain tension
On a single-speed bike, press the chain up and down halfway between the chainring and rear sprocket. A common target is about half an inch (roughly 1 cm) of movement up and down, or around an inch of total play, though advice varies a little. The chain should not be rigid and should not sag noticeably.
Turn the cranks and check at several points. Chains and sprockets are rarely perfectly round, so a chain can feel tight in one spot and slack in another. Set tension at the tightest point, not the loosest.
On a derailleur bike, a chain that is not too long or worn should stay under light tension in every gear. Visible sag, or a derailleur cage that swings far forward when you are in the small-small combination, can mean the chain is too long.
Tightening a single-speed or similar chain
In outline:
- Turn the bike over or put it in a stand.
- Loosen the rear axle nuts (and a coaster brake arm clamp if there is one).
- Pull the wheel straight back until the chain has the right tension.
- Keep the wheel centered between the chainstays and retighten the nuts firmly.
The details, tool sizes and common mistakes are in the single speed guide.
Derailleur bikes
If the chain looks loose on a geared bike, think through these options:
- The chain is worn. A stretched chain is longer than it should be, and the derailleur may be running out of range to take it up. Check wear with a gauge and replace the chain if it is past the manufacturer’s limit.
- The chain is too long. This often happens after a new chain has been fitted without sizing it. You can shorten the chain with a chain tool.
- The B-tension screw. Some guides mention this screw on the back of the rear derailleur. It sets how close the upper pulley sits to the cassette; it affects how cleanly the chain shifts and runs rather than acting as a general “tighten the chain” control. Adjust it only according to your derailleur maker’s instructions.
A chain that falls off may be a tension problem or something else entirely, so see why your bike chain keeps coming off.
When the chain is simply worn out
Wheel position cannot fix a stretched chain for long. Once the chain has worn, it also wears the teeth it runs on. Replacing it earlier is generally less expensive than replacing the whole drivetrain later.
How much does it cost to tighten a bike chain?
Costs vary by region and shop, so no fixed figure applies. A simple tension adjustment on a single-speed bike is a quick job for a shop and often a small charge, and many people do it themselves with a wrench. Replacing a chain costs more because of the part itself.
Frequently asked questions
How do I adjust chain length?
Chain length is changed by removing or adding links with a chain tool, not by tightening. See how to shorten a bike chain.
How do I put a bike chain on?
Route it over the chainring and cog (through the derailleur on a geared bike), join the ends with a quick link or the correct pin, and then check tension.
Can I tighten a chain without tools?
Axle nuts normally need a wrench. If you are working on the road and have no chain tool, see removing a bike chain without a chain tool.