Why Is My Bike Chain Slipping? Causes and Fixes
You pedal, the cranks lurch forward with a clunk, and for a split second the bike goes nowhere. A slipping chain is annoying at best and dangerous at worst — especially mid-corner or pulling away from lights. Here’s how to work out which of the three usual suspects you’ve got.
Cause 1: a worn chain (most common)
Chains wear internally — the pins and rollers elongate — until they no longer sit properly in the teeth. The giveaway: slipping happens under load (climbing, sprinting, pulling away) on the gears you use most.
Check it: a chain wear indicator drops into the links and tells you in seconds — if the 0.75% side sinks in, the chain is done. Catching it here costs one cheap part; ignore it and the chain starts skipping on a new chain’s cost, because it takes the cassette with it.
Fix: fit a new chain with a chain tool (for sizing) — a ten-minute job.
Cause 2: a worn cassette
If the chain was left long enough, the cassette’s teeth wear to little hooks and even a new chain skips. Test: slipping on one or two favourite gears regardless of load. Fix: new cassette, which needs a chain whip and lockring set — twenty minutes at home, or the reason to finally buy the toolkit.
Cause 3: stretched gear cables
Less than a year old, slipping mostly when shifting, fine once settled into a gear? That’s cable stretch making the derailleur sit slightly out of line. Fix: a turn or two of the barrel adjuster until shifts are crisp again. If the cables are years old or frayed, replace them — a full Jagwire kit makes bikes feel near-new.
The quick decision table
- Slips under load, chain old or unknown → measure the chain first
- Slips on favourite gears even with a new chain → cassette
- Hesitant shifting, otherwise fine → barrel adjuster, then cables
One safety note: a chain that slips under load can let your foot shoot off the pedal. Sort it before your next proper ride, not after.
