Shift like a pro: 10 reasons why your bike's gears aren't working as they should, and how to fix it

Say goodbye to your skipping gears, ticking chains and annoying rubbing noises as we diagnose and fix some of the most common issues with your road bike or gravel bike’s gears. 

Fettling with your derailleurs can be a bit intimidating. You don’t want to make a small problem a big one and, let's be honest, there are quite a few screws down there!

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However, if your gears aren’t working properly then you’re probably making life harder for yourself, and you’ll be wearing out components quicker and even potentially endangering yourself and the people you ride with. Here are 10 reasons why your bike gears aren’t working as they should, and what to do about it.

1. Worn chain or cassette

Before diving into any adjustments, check the wear of the drivetrain. If it’s worn then no amount of tinkering is going to solve your gear issues. When a chain wears it 'stretches', and that means that it then no longer behaves itself as it goes around the cassette or the chainrings.

Luckily it’s easy to check your chain’s wear with a cheap tool like the one pictured above. If you don’t have one then pull it away from the chainring and see how much light you can see through the gap.

> Do you need a new chain? Find out the easy way to tell

The more worn it is, the further you’ll be able to pull it; a big gap means it needs replacing. Or you can measure it with a ruler. Chains have a half-inch pitch; measure 12 full links and that should be 12 inches. If it’s a sixteenth of an inch above that, it’s time for a swap.

It’s important to stay on top of replacing your chains. If you don’t you’ll accelerate the wear of much more expensive bits such as the chainrings and cassette and then, even when you replace the chain, you’ll still get annoying noises and slippage because the rollers won’t seat properly in between the teeth.

2. It's too grubby

Sometimes all your bike needs is a bit of TLC! And by that, we mean a good clean. This is another thing to tick off before you start getting your screwdrivers out. If your chain and jockey wheels are filthy, then the system simply isn’t going to work as it should. And it’ll wear out a LOT quicker.

> How to clean your bike chain: a good way, a better way and the ultimate way

When looking at a chain, it’s actually the bits that you can’t see that need to be clean; for example, inside the rollers where any dirt will stop them from articulating properly. If you want to see how we care for our chains both when we’re in a rush and when we’re looking for every watt on race day, then click the link above.

3. Your gears need indexing

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If you're sure that your drivetrain components aren’t too worn or dirty, but your gears are noisy or seem to like changing all by themselves, then there’s a good chance your mech isn’t indexed properly. This means that the rear derailleur isn’t guiding the chain onto the right sprocket properly, and we need to adjust its position relative to the cassette.

How exactly you do this Will depend on your drivetrain. On mechanical gears, you usually use a barrel adjuster like the one above.

> 10 things you didn't know your electronic groupset could do

With electronic gears, you put the mechs into service mode and then use the shifters or an app to make adjustments.

To quickly index your gears, shift to the smallest sprocket and make sure the derailleur is correctly aligned there, with the jockey wheels directly under the sprocket.

You may need to adjust the ‘H’ limit screw on the body of the mech to tweak the position or micro-adjust an electronic set-up. On mechanical gears, take up any slack in the cable using the barrel shifter and then check the shifting across the cassette. You can tweak the cable tension to get it just right.

4. The cables need to be replaced

If you’re using mechanical gears then the cables will need replacing regularly. How often will depend on the conditions you ride in and the quality of the cables, and also how your bike is cabled: some use a full-length outer all the way from the shifter to the rear mech for example leaving nowhere for the water to get in. External cables like on the B’Twin above will likely need changing most often. As you can see, this one’s due a swap!

How will you know your cable is knackered? It’s usually most noticeable as you’re trying to move into a smaller sprocket, especially the ones right at the bottom where there’s less spring tension to pull the rusty cable through the outer. You can shift up the cassette okay, or into the big ring, but things get stuck going back down.

> How to replace a gear cable - step-by-step instructions

In some cases, you might get away with just replacing the inner gear cable but by then it’s likely that the outer cable is also full of gunk or corroded. Sometimes you might get away with just replacing a section of the cable, for example, you might need to replace the inner cable and just this section of outer cable that goes to the rear mech as quite often that’s the problem area as it’s the most exposed. Check out our article on changing your cables for a full rundown of what’s involved.

5. Derailleur hanger bent

If you’ve tried all this and your gears still aren’t playing ball then it’s possible that your mech hanger is bent. There are tools available out there to check the straightness of your mech hanger, the bit that joins the rear mech to your frame, but they’re quite specialist, and you probably don’t have one. 

A common symptom of a wonky mech hangar is if your gears work perfectly at one end of the range but then don’t at the other end. Also, if you know that your bike has taken a tumble and landed on its drive side then this is a pretty good clue.

> 1x vs 2x: Are single chainring set-ups the future of road cycling or just another marketing fad?

Sometimes it’s actually possible to look and see that it’s bent. The two jockey wheels should be sitting directly below one another in line with the sprockets; we’ve seen even new bikes come out of the box with wonky hangars.

If the hanger looks bent then it might be possible to remove it from the bike and pull it back into line, ideally, that’s a job for a bike shop with the right tool...most frames have replaceable mech hangers and they’re designed to snap, so if you don’t fancy the DIY approach and your hanger is replaceable, just order a new one!

6. B-tension screw set up wrong

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Our next port of call is the often-overlooked B-limit adjustment, which determines how far away this upper jockey is away from the cassette sprocket. The adjustment screw is usually situated at the back here by the mech hangar.

Turning clockwise will increase this gap here and vice versa. The exact recommended distance will vary from groupset to groupset but in general, you’re looking for a gap between 6mm and 14mm when you’re in your second to largest sprocket. Too far away and shifting will suffer; too close and the derailleur will hit the cassette.

7. A stiff or broken chain link

It only takes one rotten egg to ruin a cake, and it only takes one broken, damaged or stiff chain link to ruin your whole shifting experience. I’ve spent ages trying to adjust my bike’s gears before only to discover that I had a cracked outer plate on one of the links, which would cause the chain to skip every time it hit the cassette.

A seized or stiff link would also cause this to happen, so when cleaning your bike it’s a good idea to regularly inspect your chain links and make sure they’re all moving as they should. If one is damaged it could be new chain time, although you might get away with sticking in a second magic link to replace it.

8. Seized up derailleur

Sometimes, especially if you’re a bit lax with your cleaning, the issue is with the mech itself. This probably isn’t what you want to hear as the mechs are often some of the most expensive parts of the bike to replace, especially electronic ones. So it’s a good idea to clean your transmission regularly, and after every ride in the winter: salt on the roads is a real mech killer.

A derailleur relies on a motor or the pull of a cable to move up the sprockets or pull the mech over to the big ring at the front. But it’s often a simple spring that is responsible for its return. So like a rusty cable you’ll feel a sticky or seized mech most when going from a bigger to a smaller cog. This is more common on front derailleurs because they just don’t get used as much.

If the spring looks ok then it’s probably sticky pivots that are the issue. Try using something like WD40 or penetrating oil on these initially and leave it overnight to soak in, then manually articulate the mech and see if you can get it moving. If you can free the pivots up then getting a bit of wet lube or grease into the gap can stop rain or road salt getting in to seize it up again.

9. Back wheel not in properly

Another reason that your gears might not be behaving as they should is simply because your back wheel isn’t in properly. Now, this is unlikely with bikes with thru-axles as the wheel can only really sit in one place, but even so, make sure it is done up tight.

On bikes with quick releases, you need to make sure that the wheel is fully seated in the frame. The best way to do this is to always fit the wheels with the bike on the ground: apply some downward pressure to get everything nice and flush. The quick release should be a firm close, but it’s the cam action inside the lever that tightens everything up, so it doesn’t have to be at the limit of your powers to shut it!

10. The cassette is loose

Lastly, here’s one that has caught out many riders (including me): that annoying noise from the back of your bike could be caused by a loose cassette.

The lockring may be done up tight, but do the sprockets still wiggle around? If so then it needs your attention, and it will be impossible to get smooth gears until you fix it. 

Some cassettes need a spacer behind them, and if you don’t use one then all the lockring does is tighten down onto the freehub body, and your cassette is left flopping around. Another reason your cassette might be loose is that the lockring is cross-threaded, which is embarrassingly easy to do.

If you have the right tools then pop the cassette off, check that the smallest sprocket sits outboard of the freehub body like in the picture above and do it back up. We always recommend doing the lockring up by hand for the first few revolutions to avoid cross-threading Some of them really are made of cheese, so we've heard!

Let us know any of your gear issues and how you solved them in the comments section below.