Why Your Chain Keeps Falling Off

A chain that drops every few rides is annoying. A chain that drops on a climb or in traffic is dangerous. Here's what causes it and what fixes each cause.

Front derailleur limit screws

On multi-chainring bikes, if the L and H limit screws aren't set correctly, the derailleur lets the chain go too far inward (off the small ring) or outward (off the big ring).

Worn chainring teeth

Worn teeth develop a "shark fin" profile — pointed rather than square. A chain on worn teeth is more likely to jump, especially under load. If your chainring teeth look hooked or angled, it needs replacing.

Worn or stretched chain

A stretched chain doesn't mesh cleanly with sprockets and is more likely to jump on shock loads. Check chain wear here.

Chain length

Too long and it sags and drops on the small-small combination. Too short and it over-tensions the derailleur. If chain length has never been checked after a replacement, it's worth checking.

No chain guide (mountain bikes)

Off-road riding with big power inputs causes much more chain movement. A chain guide physically stops the chain dropping. If yours doesn't have one and the chain drops on rough terrain, this is the fix.

After a dropped chain

A chain that gets caught between the chainring and frame can develop stiff links. After a drop, check for kinks before riding.