· Hugo · Repairs · 4 min read
Why Your Bike Chain Skips Under Load (and How to Fix It)
A chain that skips only when you pedal hard almost always means a worn drivetrain — but four other faults can cause it too. Here's how to diagnose and fix each, in the right order.
A chain that skips, slips, or jumps the instant you put power down — standing to climb or sprinting away from a light — is one of the most common drivetrain complaints. The good news: it’s almost always traceable to one of five causes, and most are fixable at home.
The key clue is when it happens. If the chain skips only under hard pedaling but shifts and rides fine otherwise, you’re most likely looking at a worn drivetrain. Below is how to confirm that, rule out the alternatives, and fix each one.
Quick Answer
If the chain jumps forward in the same gear under load, the chain and/or cassette are worn — replace them. If it instead tries to climb sideways into another gear or clatters even with light pedaling, it’s an adjustment problem: indexing, a bent derailleur hanger, or a stiff link. Diagnose in that order before buying parts.
What Causes a Chain to Skip Under Load (Ranked)
1. Worn drivetrain (most common). Chains don’t really “stretch” — wear at the internal pins and rollers increases the chain’s effective pitch. The worn rollers no longer seat in the valleys between cassette teeth, so under high torque they ride up and over the tooth tips. Once a chain is worn, it also wears the cassette to match, so a fresh chain on an old cassette can keep skipping.
2. Incorrect rear-derailleur indexing. If cable tension is off, the chain doesn’t sit centered on the intended cog and catches on an adjacent one, slipping when you load it.
3. Bent derailleur hanger. A surprisingly large share of shifting complaints trace back to a bent hanger, usually from the bike falling on its drive side. The bent hanger angles the derailleur pulleys out of line with the cassette, so the chain enters the cog crooked and ghost-shifts or skips under power.
4. Stiff or damaged chain link. Dirt, rust, or a badly installed link can seize. A stiff link can’t flex smoothly around the small jockey wheels or cogs, producing a rhythmic skip or “flick” every few crank revolutions.
5. Chain length issues. A chain that’s too long hangs slack; too short over-stresses the system. Slack in the small-small combinations can let the chain skip across cogs under load.
How to Diagnose It (in order)
- Clean and lube first. Degrease the chain and cassette so you’re not chasing a “false” skip caused by grit or a sticky link.
- Backpedal test. Spin the cranks backward and watch the lower jockey wheel — a rhythmic jump points to a stiff link.
- Measure chain wear with a chain-checker tool (see thresholds below).
- Inspect the teeth. Look for hooked, “shark-fin” cassette teeth on your most-used cogs — a sign of wear.
- Load/road test. Pedal harder and note the behaviour: jumps forward in the same gear = wear; moves sideways toward another gear = indexing or hanger.
- Check alignment. From behind the bike, the derailleur pulleys should sit vertical and parallel under the cassette. If they’re cocked, suspect a bent hanger.
How to Fix Each Cause
| Cause | Fix | Tools / spec |
|---|---|---|
| Worn chain | Replace the chain | Chain breaker / quick-link pliers |
| Worn cassette | Replace if a new chain still skips | Cassette lockring tool + chain whip |
| Bad indexing | Adjust cable tension at the barrel adjuster | 1/4-turn increments; CCW toward larger cogs |
| Bent hanger | Straighten or replace the hanger | Hanger alignment gauge (DAG); derailleur bolt 8–10 N·m |
| Stiff link | Free the link with a chain tool or flex it side-to-side | Chain tool (loosening cradle) |
Chain-wear thresholds matter. Replace the chain at 0.5% wear for 11- and 12-speed drivetrains, or 0.75% for 6- to 10-speed. Catching a worn chain early often saves the cassette; leave it too long and you’ll be replacing both.
Indexing. Turn the barrel adjuster in quarter-turn steps — counter-clockwise shifts the derailleur toward larger cogs, clockwise toward smaller. When re-attaching a derailleur, torque the mounting bolt to 8–10 N·m (70–86 in-lb).
Worn Drivetrain vs. Adjustment Issue
| Symptom | Worn drivetrain | Adjustment / indexing |
|---|---|---|
| Pedal feel | Sudden forward drop or "bang" | Sideways clatter, clicking, ghost-shifting |
| Which gears | Often just one or two favorite gears | Many gears across the cassette |
| Chain motion | Jumps over the teeth of the same cog | Tries to climb to an adjacent cog |
| When it happens | Only under hard pedaling | Can click or hesitate even with light pedaling in a stand |
What It Costs (2026)
DIY parts: a new chain runs about $15–30, a cassette $30–80, and cables and housing $15–30. A basic drivetrain tool kit (chain checker, breaker, lockring tool, chain whip) is a one-time $60–120 and pays for itself quickly.
Bike shop: a derailleur-hanger alignment is roughly $10–25, and a full chain-and-cassette replacement (parts plus labor) commonly lands around $100–150. Many shops add about a 10% premium for guaranteed same-day turnaround.
Is It Safe to Keep Riding?
No — keep the fixes ahead of the miles. When a chain skips under load, the pedals can suddenly drop, which is a real crash risk, especially out of the saddle. Diagnose and fix it before your next hard effort.
Frequently Asked Questions
Why does my bike chain skip when pedaling hard but shifts fine?
That pattern almost always means a worn chain and/or cassette. Under high torque the worn rollers ride up over the cassette teeth instead of seating between them, so the chain jumps forward in the same gear. Shifting can still feel normal because indexing is unaffected. Measure chain wear with a chain checker and replace at 0.5% (11/12-speed) or 0.75% (6–10 speed).
Why does my new chain skip on my old cassette?
Because the old cassette is worn to match the old chain. A fresh, correctly-pitched chain no longer meshes with the hooked, worn teeth, so it skips — usually on the most-used cogs first. If a new chain skips on an old cassette, replace the cassette too.
Why does the chain only skip when I stand up to climb?
Standing puts maximum torque through the drivetrain, which exposes wear and alignment problems that stay hidden under light pedaling. The usual culprits are a worn chain/cassette or a bent derailleur hanger letting the chain enter the cog at an angle.
Is it safe to keep riding if the chain skips?
No. A chain that skips under load can cause the pedals to drop suddenly, which can throw you off balance or cause a crash — particularly when standing. Fix the cause before riding hard again.
Can a dirty chain cause skipping?
Yes. Dirt, grit, and rust can seize a link so it can't flex smoothly around the jockey wheels and cogs, producing a rhythmic skip. Always clean and lube the drivetrain first — it rules out false skips before you start replacing parts.
Sources
- Park Tool — drivetrain wear, chain-checker use, and derailleur adjustment guides
- Shimano dealer service instructions (e.g. RD-5600, SI-5VN0B-001) — B-gap and torque specs
- SRAM service guides — derailleur capacity and B-gap requirements
- Sheldon Brown — drivetrain and gearing reference