Having a chain fall of while you are riding your bicycle is annoying, if not dangerous! However it also can be extremely difficult for a beginner to be able to figure out why in the world it is doing this.
The most popular reasons, and easiest to fix range from the chain being worn out, or that one of your derailleurs just isn’t as accurate as you would like.
Please note, if you recently bought a bike from a big box retailer and are having these issues, you will want to take your bike to a shop for a quick tune up! Read through this article to learn why that is.
If taking your bike to a shop is not an option for some reason, these different things is where I would start on my hunt for the culprit of your chain falling off.
How does a chain work?
Whenever you are working on something, including a bicycle, it is important to understand how something works, so that you can tell when something works.
Since this article can’t quite describe everything in depth, I’ll give you the quick answer as to how a chain works on a bike.
A chain sits on the teeth of the front crankset (which has your pedals attached to it), and the rear chainring (where you generally have more gears).
It also is guided by the rear derailleur and the front gear derailleur. When you shift gears, these derailleurs will move the chain, and guide them onto the corresponding gear that you have chosen.
While this all sounds relatively simple, if anything in that drivetrain isn’t quite right, it can cause issues, such as a chain falling off.
Before you start
Before you get too far into your diagnostics, you will want to put your bike into position for the work!
Flip your bike over onto its handlebars and seat, and make sure that you are able to spin the pedals to move the wheels. This will allow you to test out all of the components we are going to be looking at.
1. Something is loose
Something I learned from my Dad a long time ago, is to start with the cheapest issue and work your way to the most expensive component. While that was intended for cars, it works in this situation as well.
Before you start wanting to replace anything, move through all of your drivetrain components and check if anything is loose. Don’t pull too hard at parts and make them bend or break, but just wiggle them a little bit to see if they rattle or move slightly.
If there is something loose, tighten it down (not too tight) and see if you can run through your gears without the chain falling off. For these cases, something like this multi-tool that is made specifically for bicycles would be perfect.
2. Lower derailleur is not accurate
While I am sure there are many other things on this list that may be the reason for your bike chain falling off, this was the most recent reason for my personal bike’s chain to fall off.
When the bike is upside down, spin the pedals and watch your rear derailleur as you shift through the different gears.
If the derailleur seems to be slightly off center to the gear it should be in, this could be causing the problem!
In my case, my bike was actually one whole gear off, meaning every time I put my bike into the 7th gear on the back, the chain would fall off. It also meant, I could never put my bike into first gear, leaving me with only 5 gears in the back.
Make sure to adjust your derailleur to be exactly center over the gear your want it to be.
3. Front derailleur is not accurate
While not quite as common of an issue as the rear derailleur, your front derailleur can also be off as well.
Follow the same steps as the rear, but on the front, and you will quickly find if this is the issue, and allow you to be able to adjust it as needed.
4. Chain is too long
If you recently replaced your chain, it is possible that the chain may be too long.
Whenever you change out your chain, make sure to line it perfectly up to your old chain and remove or add links as necessary. You will need to get yourself a too like this chain splitter to do this correctly! Its a tool that is indispensable when maintaining your bike.
If you have already discarded your old chain, it will be a bit more difficult, but adjust it until you don’t have so much slack, if this is the issue.
5. Chain or components are worn out
Like anything that is used regularly, sometimes parts just get worn out. They may not be damaged from being bent, or hit hard, but it may just be time to replace components.
Teeth on your crankset or chainring may be starting to wear, allowing the chain to slip off without meaning to. Or derailleurs just aren’t working like they should because they are either worn out, or things like the pulley spring is no longer working as it should.
Bikes require maintenance just like cars, and you should check these things regularly to see if it is time to start replacing components.
6. Twisting the shifter too far
I think this is something most people run into! Your bike is running fine, and probably has happened to everyone at least once.
Your bike only has 7 gears on the rear, but for some reason you aren’t paying attention and you are trying to put it into the non-existent 8th gear.
This will cause the derrailleur to incorrectly extend itself a little too far, and cause the chain to fall off.
An easy solution is to just not do that…
Of course, there are many other reasons that a chain can come off like a dirty (or even weathered) drivetrain, bent components and more. However these are all great places to check first!
Keeping your bike in tip-top shape is important, and I hope you enjoy your bike more and more every day!