Is it the chain skipping or the pedals slipping?
Riders use “slipping” for a few different feelings, and the cause depends on which one you have.
- Skipping: the pedals suddenly drop or jump forward, then catch again, usually under hard effort and often in one gear. This is typically chain-and-cog wear or a gear adjustment problem.
- Freewheeling or no drive: the pedals spin with no resistance, sometimes with a ratcheting sound. That suggests a problem inside the rear hub, in the freehub or freewheel; see also wheel not turning when you pedal.
- Chain falling off: covered in why your bike chain keeps coming off.
Test it safely. Lift the rear wheel, turn the pedals by hand and shift through the gears, then take a short ride on flat, quiet ground, pressing harder on the pedals in each gear. Note which gears cause the problem.
Worn chain and cassette
This is a very common reason for skipping under load. As a chain wears it effectively lengthens, and the cog teeth wear into a shape that matches the old chain. Put a new chain on worn cogs and it may skip, usually in the gears you use most. A chain that skips in only one or two gears often points to cog wear in those spots.
What you can do:
- Measure the chain with a wear gauge, and check the manufacturer’s guidance for the replacement point for your chain.
- If the chain is worn but the cassette is not yet badly worn, a new chain may fix it. If the cassette is also worn, replacing the cassette and chain together is usual.
- Look at the chainring teeth for a hooked or shark-fin shape.
Gear indexing and cable tension
If the chain is not sitting precisely over the chosen cog, it can ride on the edge of a tooth and slip under load. Cables stretch over time, particularly on a new bike, and shifting drifts out of adjustment.
- If the chain hesitates when shifting, or makes noise in particular gears, indexing is a likely cause; see also why your bike gears keep slipping.
- A small turn of the barrel adjuster at the derailleur or shifter changes cable tension. Turn in small increments and test after each.
- A bent derailleur hanger can make adjustment impossible, because the derailleur never lines up with the cogs.
A stiff link
A link that does not flex passes through the derailleur and onto the teeth awkwardly, which can produce a regular skip once per chain revolution. Turn the pedals slowly and watch the chain pass through the rear derailleur pulleys, where a stiff link often kinks or jumps. Flexing the link by hand and adding lubricant often frees it. A link that was recently joined may be the cause, especially if a pin was pushed back in. Rejoining with a quick link made for your chain is generally safer, as discussed in how to shorten a bike chain.
Freehub or freewheel problems
If the chain and cogs look fine but the pedals still spin without driving, the freehub’s pawls or ratchet may be worn, dirty or short of lubricant. Servicing differs between hub models, so consult the hub maker’s instructions or a shop.
Single-speed and fixed bikes
On a single-speed bike, a chain that is too loose can skip or pop off under hard pedaling, while one that is too tight causes drag and wear. See tightening a single speed bike chain.
How to check if a chain is too loose
On a single-speed bike, push the chain up and down midway between the sprockets; a small amount of play is normal. On a geared bike the derailleur takes up slack, so a chain that sags noticeably in some gear combinations might be too long or worn. How to tighten a bike chain covers both cases.
Frequently asked questions
Why does my bike chain fall off when I pedal backwards?
On a geared bike, pedaling backwards slackens the top of the chain and the derailleur can let it drop. It is not unusual, but it may also hint at slack or poor derailleur setup. It is best to avoid pedaling backwards.
How do I fix a bicycle gear that slips?
Start by cleaning and lubricating the chain, then check wear, then adjust cable tension with the barrel adjuster in small turns.
What causes a bicycle chain to break?
Wear, shifting under heavy load, improper joining and bent parts are common reasons. See why bike chains break.