Gears Not Shifting Properly? Here's Why

Skipping, clicking, hesitating, or refusing to shift — gear problems are frustrating and surprisingly common. Here's what's going on and what you can do about it.

How bike gears work (the basics)

Your bike's gears are controlled by a derailleur — a spring-loaded mechanism that moves the chain between sprockets. When you click the shifter, it pulls or releases a cable, which moves the derailleur. The system relies on precise cable tension to position the chain correctly on each sprocket.

When that tension is off — even by a fraction — gears skip, hesitate, or refuse to shift.

Common causes of gear problems

1. Cable stretch

This is the most common cause, especially on newer bikes. Gear cables stretch slightly during the first few weeks of riding, which throws the indexing off. The fix is a simple cable tension adjustment — usually a quarter-turn of the barrel adjuster.

• Most common on bikes less than 6 months old
• Symptoms: gears hesitate or skip under load
• Fix: turn the barrel adjuster anti-clockwise in small increments

2. Dirty or corroded cables

Over time, moisture and grit get inside the cable housing, causing friction. The derailleur can't move freely, so shifts become sluggish or incomplete. This is especially common on bikes ridden in winter or stored outdoors.

• Symptoms: slow, sticky shifting — especially in one direction
• Fix: cable and housing replacement (a mechanic job)

3. Worn chain

A stretched chain doesn't sit properly on the sprockets, causing skipping — especially under hard pedalling. If you ignore a worn chain, it damages the cassette and chainrings too, turning a £15 fix into a £60+ one.

• Check chain wear with a chain checker tool (or ask your mechanic)
• Replace at 0.5% wear for 10/11/12-speed, 0.75% for 8/9-speed
• Read more: Is my bike chain worn out? →

4. Bent derailleur hanger

The derailleur hanger is a small, sacrificial piece of metal that attaches the rear derailleur to the frame. If your bike falls over or you knock the derailleur, the hanger bends — and even a tiny bend throws the gear alignment off completely.

• Symptoms: gears work on some sprockets but not others, chain drops
• Fix: hanger straightening or replacement (mechanic job — needs a specialist tool)

5. Worn cassette or chainrings

If you've been riding on a worn chain for too long, the teeth on your cassette and chainrings wear into a "shark fin" shape. A new chain on worn sprockets will skip badly because the teeth no longer match the chain's pitch.

• Symptoms: new chain skips on certain gears (usually your most-used ones)
• Fix: cassette and/or chainring replacement

6. Derailleur limit screws

Limit screws prevent the derailleur from moving too far inward or outward. If they're set wrong, the chain can't reach the biggest or smallest sprocket — or worse, it drops off entirely.

• Symptoms: can't reach top or bottom gear, chain drops off
• Fix: careful adjustment of the H and L limit screws

What you can try at home

• Barrel adjuster: if gears hesitate shifting to bigger sprockets, turn the barrel adjuster anti-clockwise a quarter turn at a time
• Clean and lube the chain: a dirty chain causes poor shifting
• Check for obvious damage: look at the derailleur hanger — is it straight?
• Check cable tension: is the cable frayed or kinked anywhere?

When to call a mechanic

• Bent derailleur hanger — needs a specialist alignment tool
• Worn chain, cassette, or chainrings — needs measuring and replacing
• Corroded cables — full cable and housing replacement
• Persistent skipping after adjustment — usually a wear issue
• Chain dropping off regularly — limit screw or hanger issue