Why Are My Bike Gears Slipping? Common Causes and What to Do

Why are my bike gears slipping? If the pedals have suddenly given way under you, the chain has jumped between cogs or your gears keep clicking and refusing to settle, this guide is for you. We are Cycle Revival, an independent bike shop and cycle workshop in Heathfield, East Sussex, and adjusting gears is one of the basic repairs we carry out on all kinds of bikes. Below we explain what gear slipping feels like, the most common reasons it happens, the simple checks you can do at home and when it is worth bringing your bike in to us, so you can get back to smooth, confident riding.

What Does Gear Slipping Feel Like?

Gear slipping usually shows up when you put power through the pedals, such as pulling away at a junction or climbing a hill. The chain might jump to a different cog on its own, skip over the teeth with a clunk, or feel as though it briefly loses grip before catching again. You may also hear a rattle or a ticking noise from the back of the bike in certain gears.

If you are asking yourself why are my bike gears slipping, it helps to notice when it happens. Does it happen in every gear or just one or two? Only when you push hard? Did it start after a knock or after new parts were fitted? These clues point towards the cause. A sudden slip under load can also throw you off balance or make your foot come off the pedal, so it is worth getting to the bottom of it rather than riding on and hoping it goes away.

Why Are My Bike Gears Slipping?

Most slipping comes down to the drivetrain, which is the chain, the cogs on the back wheel (the cassette or freewheel), the chainrings at the front, and the derailleurs and cables that move the chain between them. These parts wear together and rely on each other, so a problem with one often shows up as poor shifting across the whole system. Here are the most common causes.

Your Gear Cable Needs Adjusting

On most bikes, the rear derailleur is moved by a cable that runs back from the shifter. Each click of the shifter should line the chain up with the next cog, which is known as indexing. If the cable tension drifts, the derailleur sits slightly between two cogs and the chain can hop back and forth, especially under load. This is common on new bikes, as fresh cables and outer housing settle in over the first few weeks of riding. If you are wondering why are my bike gears slipping on a bike you have only just bought, cable settling is a likely reason. It is usually corrected with small turns of the barrel adjuster, the little threaded barrel where the cable enters the rear derailleur or shifter. Park Tool’s guide to rear derailleur adjustment explains the process in detail.

Your Chain Is Worn

As a chain covers the miles, its pins and rollers wear and the chain gradually gets longer, which riders often call chain stretch. A worn chain no longer sits snugly in the teeth of the cogs, so when you press hard it can ride up and skip. A chain checker tool is the quickest way to measure wear, and our blog on how often you should replace a bike chain covers the signs to look out for. If your chain mainly slips when you are really pushing, our earlier post on why your chain slips when pedalling hard is worth a read too.

Your Cassette or Chainrings Are Worn

A chain that is left on too long wears the teeth of the cogs to match it. Worn teeth can start to look hooked or pointed rather than evenly shaped. The catch is that a new chain fitted to a worn cassette will often skip, usually on the cogs you use most, because the new chain does not mesh with the worn teeth. If you have fitted a new chain and the slipping started straight away, a worn cassette is a common reason, and the two may need replacing together. Replacing your chain before it gets too worn helps protect the cassette and chainrings, which usually cost more to replace.

Your Derailleur Hanger Is Bent

The derailleur hanger is the small metal bracket that connects the rear derailleur to the frame. On many bikes it is a separate, replaceable part, made so that it bends in a knock instead of the frame. That means it can be bent quite easily if the bike falls over on its drive side, gets knocked in a bike rack or is squashed in the back of a car. Even a slight bend throws the derailleur out of line with the cogs, and cable adjustment alone will not fully fix it. A badly bent hanger can also let the derailleur catch the spokes when you shift into the largest cog, which can cause serious damage, so this is one to get checked. A hanger can often be realigned with a specialist tool, or replaced if it is too far gone, as shown in Park Tool’s guide to derailleur hanger replacement.

Dirt, Grime and Sticky Cables

Autumn and winter riding around East Sussex means wet lanes, mud and grit, and a lot of that ends up on your drivetrain. A dirty, dry chain does not move across the cogs as cleanly, and grit inside the cable housing adds friction, so the derailleur cannot respond to the shifter accurately. Frayed or corroded cables cause the same problem. A good clean and fresh lube often makes a noticeable difference, and our guide to cleaning a bike chain shows you how. If shifting still feels sluggish afterwards, the cables and housing may need replacing.

A Stiff Link in the Chain

Sometimes one link in the chain stops pivoting freely, for example after a chain has been joined or when rust has set in. As that stiff link passes through the rear derailleur it can make the chain jump, which feels a lot like slipping gears and tends to happen at regular intervals as you pedal. Slowly backpedalling and watching the chain run through the derailleur will usually show up a link that kinks rather than bending smoothly.

When It Might Not Be Your Gears

If the pedals suddenly spin with no drive at all, rather than the chain jumping between cogs, the problem may be inside the rear hub or freewheel. Most of these use small spring-loaded pawls that catch when you pedal, and if they are worn, dirty or sticking they can fail to engage. This needs looking at by a mechanic.

Simple Checks You Can Do at Home

Before booking anything in, there are a few things you can look at yourself.

• Clean and lube the chain, then see if the shifting improves.
• Stand behind the bike and look at the rear derailleur. If it looks out of line with the cogs or tilted in towards the wheel, the hanger may be bent.
• Backpedal slowly and watch for a stiff link.
• Check the chain for wear with a chain checker.
• Lift the back wheel and shift through every gear, listening for noise or hesitation.

Working through these checks will often answer the question of why are my bike gears slipping. If you are confident with tools, small turns of the barrel adjuster may sort out the cable tension. If you are not sure, leave the limit screws on the derailleur alone, as setting these wrong can let the chain drop off the cogs or push the derailleur into the spokes.

When to Bring Your Bike Into Our Workshop

If the slipping carries on after a clean and a small adjustment, or you suspect a bent hanger, worn parts or a hub problem, our team in Heathfield can help. With over 40 years of experience in the trade, we can check and adjust your gears as part of a bike repair, or look at the whole drivetrain during a bike service. We offer two levels of service, a full external service or a full strip-down clean and rebuild, and our post on what actually happens in a full bike service explains what is involved. Not sure what your bike needs? Give us a call and we can advise you.

Get In Touch

Why are my bike gears slipping is a question with a few possible answers, but most of the time it comes down to cable tension, worn parts, a bent hanger or a drivetrain that needs a good clean. Sorting it early makes your riding safer and can stop a worn chain from wearing out more expensive parts. If you would like us to take a look, the team at Cycle Revival is here to help. Give the shop a call on 01435 866118, email us or fill out our contact form, and we will help get your gears running smoothly again.