What you need
- A wrench or socket that fits your rear axle nuts. Sizes vary; 15 mm is common, but check yours.
- If you have a coaster brake, a smaller wrench or screwdriver for the brake arm clamp.
- A bike stand, or a soft surface if you turn the bike upside down on its saddle and handlebars.
- Optional: a rag and lubricant, since you will likely be handling the chain.
Bikes with quick-release rear wheels are less common in this category, but the same principle applies: the wheel slides in horizontal dropouts.
Step by step
- Position the bike. Use a stand or turn it over. Take care not to damage cables, shifters or the saddle.
- Loosen the coaster brake arm, if present. The arm clamps to the chainstay. Loosen it enough that the axle can move.
- Loosen both axle nuts. Slacken them until the wheel can slide back and forth by hand but is not falling out. Loosening only one side makes alignment harder.
- Pull the wheel backward. Move it straight back in the dropouts until the chain is taut.
- Check the tension. Press the chain up and down halfway between the sprockets. A commonly given target is about half an inch (roughly 1 cm) of movement either way, or around an inch total. Not completely slack, not guitar-string tight.
- Center the wheel. Look from behind, or check the gaps either side of the tire, and make sure the wheel sits evenly between the chainstays and the tire does not touch the frame.
- Tighten the axle nuts. Hold the wheel in position, tighten one side, then the other, firmly. Re-check that the wheel did not shift and the tension is unchanged. Retighten the coaster brake arm.
- Spin the wheel and listen for rubbing, then take a short test ride.
How tight is right?
A bit of slack is normal and desirable. A chain pulled too tight puts extra load on the bearings in the hub and bottom bracket and can speed up wear. One that is too loose can drop off or skip under hard pedaling, a problem described in bike chain slipping under hard pedaling.
If the chain is tight in some places and loose in others
Spin the cranks slowly and feel the chain at several points. A chain ring that is slightly off-center, a bent sprocket or an uneven chain can all create tight spots. Set tension at the tightest point. If the difference is large, a bent chainring or worn parts may be the cause, and a shop can help.
Coaster brake bikes
Moving the wheel also moves the brake arm. The arm must be reattached to the frame afterward, at roughly the angle it was before, or the brake may not work well. If you are unsure, have a shop check the brake after adjustment, and test it at low speed before riding normally.
When there is not enough room in the dropouts
If the wheel is already at the very front of the slot and the chain is still slack, the chain is probably stretched or too long for the gearing. Options include:
- Removing a link, or a pair of links on a standard chain (see how to shorten a bike chain).
- Fitting a half-link, if your chain is compatible.
- Fitting a chain tensioner, if your frame has vertical dropouts or no way to move the wheel.
- Replacing a worn chain.
On frames with vertical dropouts, wheel position does not adjust tension at all, so a tensioner or an eccentric bottom bracket is used.
Other questions
How do I tighten a chain on a bike with gears?
Geared bikes do not use wheel position to set tension; see how to tighten a bike chain.
Can I do this by myself?
Yes, generally. Holding the wheel in position while tightening the nut is the awkward part; some people clamp or tie the wheel in place or work with the bike in a stand.
What about a motorcycle chain?
Motorcycle chains are adjusted differently and the safety stakes are higher. Use the owner’s manual for your motorcycle rather than bicycle instructions.