If your bike chain keeps falling off it may be because it is too loose, however there are several other reasons for chain jams and slips.
Is your bike chain falling off?
Everybody's bike chain comes off at some point, whether you are a road cyclist, on a long distance bike tour, and especially if you're a mountain biker.
After all, if you're down-hilling and your mountain bike chain comes off when you land especially heavily, it's only to be expected!
Normally, you can get away with pedaling a dropped chain back on and carry on with the ride.
What if the bike chain falls off more regularly though?
When your bike chain falls off every time you hit a small bump on the trail or change gear on an incline, then it is likely that your chain is too loose. This can be caused by a variety of things, including chain stretch, bad derailleur adjustment, or even a stiff link on the chain.
Sometimes, you will need to replace the bicycle chain. Other times, just some small adjustments may get the chain running more smoothly again.
It might not always be because the chain is too loose though. Sometimes, chains that are too tight will drop, and chains that are the perfect length will fall off if there are other issues with the derailleur or drivetrain.
Related: Troubleshooting Bike Problems
How to Fix a Chain that Keeps Falling Off
In this blog post, I'll list some of the main reasons why your chain keeps coming off and how to fix it.
The chain is as dirty AF!
If you've been out mountain biking, and the last time you cleaned your chain was like never, you can expect that dirt and grime will have built up over time.
This can cause the chain to slip, resulting in it falling off. The solution is simple: give your chain and cassette a thorough clean with a degreaser.
Regular chain cleaning and lubrication will ensure that your bike runs smoother and quieter for longer. Chain maintenance can seem a hassle, but it stops a lot of problems in the long run.
Chain has a stiff link
Occasionally, a link on the chain can become stiff and not move as freely. This can cause the chain to skip over a tooth on either the front chain ring, or cassette on the rear wheel, resulting in it falling off.
To identify a stiff link, put you bike up on a bike stand, and try shifting through all your gears slowly with one hand on the derailleur and another feeling for any tight spots on the chain. If you do find a stiff link, use pliers to wiggle it around, put some oil on, and see if that does the trick.
In situations where the stiff links is actually a bent link, you may need to replace the chain, as any alteration of it will make the chain weak, causing it to break at some point in the future.
The chain is too loose or too tight
Chain length can also be the cause of some problems. When a chain is too long, it will be loose and easily slip off the cassette and derailleur under pressure. On the other hand, a tight chain can cause it to skip when you change gears.
You can get chain tensioners which may help with looser chains, but in all honesty, as you can get bicycle chains relatively cheaply, it might be just better to replace the chain with a new one.
Rear Derailleur Hanger Bent
People who have been riding their bike over rough paths and forest areas might want to check if their rear derailleur hanger has become bent or otherwise damaged. This is because a bent derailleur hanger will cause the rear derailleur to move slightly, resulting in an uneven chain tension and causing it to slip off.
To check if it's your rear derailleur hanger that is causing the problem, check if the pulley wheels of your rear cassette are aligned with each other. If they are not, you may need to straighten the derailleur hanger or replace it with a new one.
The rear derailleur is out of alignment
If your chain keeps slipping off when you change gears, it may be because the rear derailleur isn't aligned properly. It's worth checking to make sure that everything is in line and there are no obstructions stopping the chain from flowing freely through the cassette.
Front Derailleur Issues
If your bike has a double chainring, it could be that the front derailleur is misaligned or out of position. This can cause your chain to slip off when you try and change gears on the front chainrings. On occasion, a chain may even get wedged in between the two front chainrings – it's an absolute pain when this happens!
Adjusting the front derailleur limit screws may solve some of the issues, but test it out thoroughly before taking the bike on an extended ride.
The chain is old and needs replacing
Time to be honest. When was the last time you changed the chain on your bicycle? In fact, did you ever change it?
It's amazing how the weeks turn into months and then years. Before you know it, you've been using a bike for a couple of years and never changed the chain once!
Over time, the chain will stretch and cause it to slip off the cogs if it's not replaced. You can measure a chain to see if it has stretched, but if you've not changed the chain in over a year, save yourself the time and just put a new one on. You'll find that you bike is a lot easier to cycle that way!
Related: Why is my bike hard to pedal
You just replaced a chain with the wrong size
Congrats, you realised that you needed a new chain for your bike, but did you get the length of it right? A chain with too much slack is as problematic as one with no slack at all.
When replacing a chain on your bike, you'll need to make sure that you get the correct size. The wrong sized chain can cause it to slip off more than usual and this is especially true with single speed bikes.
To measure for the right sized chain, you can lay the new and old chain side by side, or count the number of links in the old chain.
Replaced a chain with the wrong type
When replacing your worn chain with a new one, it's important to get the right chain. You will see chains marked as single speed, 9 speed, 10 speed, 11 speed etc.
Using the wrong type of chain will mean that it won't fit into your cassette and derailleur correctly and can cause slipping off problems as well. Before you purchase a new chain, check to make sure that it is compatible with your bike's drivetrain components.
If you've packed up your bike to transport it on a plane and the box hasn't been handled with care (and trust me, it won't!), you may find that the chainring has been bent during transit.
It's very rare, but it can happen. A bent chainring will cause the chain to slip off when pedaling, so if this is the case you'll need to replace or repair it.
You can have a local bike shop assess and fix the problem for you (ie, replacing the chainring) or try DIY'ing it with some pliers. Just take extra care not to damage anything else in the process.
Related: Best Bike Multi-Tools
Drivetrain Components Worn
Just as your chain needs replacing every few thousand miles, so too will your rear cassette on derailleur bikes.
This is because is you cycle, not only does the chain wear, but the contact with the rear cassette causes the teeth to wear down.
If you've just swapped the bicycle chain but kept the cassette on the rear wheel, you may find that the chain slips for the first 50 or 100 miles. This will eventually stop when the chain has worn enough to match the cassette.
It's advised to swap out rear cassettes on derailleur bikes every two or three chain changes for optimal performance.
Chain Drops Rohloff Hub
I know that Rohloff hubs and other internally geared hubs are not very common, but as I have a Rohloff equipped bike for bike touring, I thought I would mention it here!
A Rohloff hub is often used on touring and off-road bikes due to its ability to handle a wide range of gears and its ability to shift smoothly even under heavy load.
The hub is designed with 14 gears that are evenly spaced, allowing riders to easily find the right gear for any situation. It is also known for its durability and reliability, as it requires minimal maintenance and is resistant to damage from water and dirt.
There are two reasons why a chain will slip on Rohloff equipped bikes. The first, is that the chain tension has become slack over time. This means the chain needs replacing, or in the case of eccentric bottom brackets, altering to remove the chain slack.
The second, is that either the rear sprocket or front chainring has got worn teeth. They will either need replacing, or in the case of some bikes (mine included), the rear sprocket can be reversed.
Chain Drop FAQ
If your chain consistently slips or drops, these are some of the most common questions and answers you should know:
How do I keep my chain from falling off?
Regular bicycle maintenance checks and occasional replacements should help reduce problems with dropped chains and ensure a smoother ride overall!
How often do I need to replace a bicycle chain?
For maximum cycling efficiency, it is suggested to replace bike chains every 2000 or 3000 miles. When bike touring, cyclists might choose to stretch this out, and replace a chain every 5000 miles or so.
What causes chain to fall off?
The most common causes are a stretched chain, an incorrectly adjusted rear derailleur, worn-out cassette or chainring, dirt buildup, misalignment issues, or incompatibility with parts.
What are drivetrain bolts?
Drivetrain bolts are a component of the drivetrain system on a bicycle. If there is more than one front chainring, the drivetrain bolts or chainring bolts attach them to each other, and then to the crankset.
Where does the bicycle chain fall off?
A bike chain can fall off on either the front or back of the bike depending on what the issue is.
What does a chain tool do?
A chain tool, sometimes called a chain breaker, can both break a chains links to remove an old one, and fit together a chain link when installing a new chain. Chain tools can be dedicated tools, or come as part of a bike multi-tool.
– Dave Briggs
Dave has cycled around most of the world on different bikepacking trips, and is always looking for the best way to make a cycling tour easier. This guide to reasons why bike chains keep falling off and how to fix it is one of a series of troubleshooting guide to bike problems you will find on this blog.
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