9 Reasons Why Your Bike Chain Keeps Falling Off & How To Fix

by Media Heroes.

Cycling is one of Australia’s most popular pastimes, and has also become a healthy way to commute into work. But as with any machine with moving parts, bikes have problems, especially its most complicated feature: the drivetrain. If you’re wondering why your bike chain keeps falling off the drivetrain, there’s plenty of reasons for it happening, many of which are fairly simple fixes.

These are the most common reasons why your bike chain keeps falling off, and some quick tips on how to prevent it from happening.

1. Loose screws/bolts on drivetrain

This is a common reason for bike chains falling off. If any of the screws or bolts that secure your drivetrain are loose, the entire system can shift about while you’re riding, which can easily cause the chain to come loose.

To fix this issue, simply use a screwdriver to tighten any screws and bolts you find on your derailleur. The derailleur is the gear system that allows you to shift gears, and looks like the below.

Rear Derailleur

Rear derailleur

Also tighten any bolts on the other part of the derailleur, on your front wheel. This looks something like this:

Loose Screw Chain

Front derailleur. Image from Park Tool

2. Stretched chain

Chains can elongate over time, becoming looser and looser until it struggles to stay on the drivetrain’s cassette (the big multi-layered cog). This might looks something like the below:

Stretched Chain

​​Image from Reddit

If your chain keeping coming off while you’re pedalling hard, this is also evidence that it’s elongated and needs to be fixed. Thankfully, it’s pretty easy to tighten an elongated chain—here’s a great guide from Cyclingity on how to do so.

3. Chain too long

This is a similar problem to an elongated chain, but is usually caused by purchasing the wrong-sized chain for the bike. When the chain is too long, the derailleur won’t be able to pick up the extra chain length, which can cause it to easily slip off.

If you can, the easiest way to fix this problem is to return the chain for the correct size. If that’s not possible, you can remove some links from the chain by following this handy guide from WikiHow. You’ll need a universal chain tool to complete this process.

4. Dirty chain

Filthy Rusty Chain

A filthy bike chain like this is bad news

Dirty chains are bad news for bikes. They will make the chain and drivetrain wear down faster, reduce the flexibility of the links, and degrade your cycling performance. A dirty chain can also be the reason it keeps falling off the drivetrain.

Keeping your chain in good condition is crucial for these reasons, and should be regularly cleaned and lubricated. Check out our article on how to clean your bike, which includes lubrications tips.

5. Stiff chain link

Stiff chain links are often caused by improper installation, but can also be caused by overly aggressive gear shifting, as well as rust. Because they fail to curve around the bike’s cassette, they can cause the entire chain to fall off.

You can fix stiff chain links by following this process:

  1. Lube your chain—often, lubing your chain can be enough to fix a stiff link. Be sure to use a good quality lubricant like Smoove Lube or Rock n Roll Gold. Don’t use WD-40!
  2. Fix the stiff link with a chain tool—if you have a chain tool handy, you can locate the stiff link by seeing when the chain jumps as it passes over the lower jockey wheel, and then loosen it with the tool.
  3. Fix the stiff link by hand—you can also try loosening the link by hand. Be sure to turn the surrounding links to 90 degrees on either side.

If this doesn’t fix the issue, we recommend taking your bike to a pro. You may end up needing a new chain entirely.

6. Worn cassette cogs/teeth

The teeth (cogs) on your cassette are how your bike’s chain latches onto the drivetrain, and allows the entire system to work. When a bike is used excessively, not maintained, or consistently assaulted with grime, salt, and rain, the tip of the teeth can quickly wear down, which makes it much easier for the chain to slip off. This can make your bike extremely dangerous, especially if you ride on busy roads.

Worn Chain Cassette

The difference between worn cassette teeth, and new cassette teeth. Image from Road Cycling UK

The best thing to do here is to take your bike to a professional, who can determine the best way to fix the problem. They might recommend a new cassette, and will also be able to service the bike to perform more efficiently.

7. Misaligned derailleurs

Misaligned derailleurs affect the entire gear system. When out of alignment, it’s much harder for the chain to shift over to another gear, and can completely skip gears, or even fall off mid-ride. This is dangerous and can also cause serious long term damage to your bike.

Check out these two great videos on how to adjust your front or rear derailleurs, to properly realign them.

8. Low-quality shifters

Low quality or budget shifters can fail to keep the proper cable tension when riding, which can cause your bike chain to fall off. To test this, you can pull the shifter cable and observe any loss in tension.

Unfortunately, this fix usually requires new shifters. But it’s always worth taking the bike to a professional to see if they have any solutions.

9. Bumps

Sometimes, your chain can come off when you go over a large bump, which is a sign that your chain needs to be tightened. For help with this, check out this comprehensive guide on how to tighten a bike chain.

Why your bike chain keeps falling off—summary

The last thing you want is for your chain to fall off while you’re riding. It can be incredibly dangerous for both yourself and riders around you. Now that we’ve covered the nine most common reasons for your bike chain falling off, we hope you have the information you need to make a quick diagnosis, and the knowledge to fix the issue.

Good luck!