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Chain Keep Coming Off Bike When Changing Gears? 11 Reasons + Fixes

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Many of us fondly remember when we first learned to find our balance and overcome the fear of falling off a bike. Bicycles are an integral part of most of our daily lives. Simple as the machine seems on the surface, a bike comprises many moving parts working together.

One very integral part is the bike chain. While it might not be the most exciting part of the bike’s assembly, you won’t be able to travel all that far without its functionality.

The biggest issue with the chain is that it comes off during gear changes. There can be many reasons for that malfunction, including a dirty chain, stiff links, the chain needing to be correctly tight, the wrong length, or the wrong length and the wrong type of chain.

It is crucial to fully understand how the bike chain works, its different parts, and what can go wrong to learn how to fix it. We will walk you through all that in this blog. Let’s get started.

Chain Keep Coming Off Bike When Changing Gears

Aspects of the Bike Chain

Structure of Bike Chain

A bike chain is formed by connecting links. Most chains consist of wide and narrow links repeatedly alternating the entire length. Two side plates on every link are held together through rivets, also called pins. The shoulder of the outer link houses the roller, and some chains can have separate brushing on each of the sides of the roller.

The chain’s internal link is narrower than the outer link, with a smaller space between them. The standard distance between the two is around half an inch. The alternating narrow and wider chainring teeth allow for a strong connection between the chain and teeth. This is done on single-ring drivetrains. (Source)

This can’t be achieved on drivetrains with multiple rings. This is because the chain’s position can’t be deduced when chainrings are shifted. Therefore, drivetrains with multiple chainrings have teeth of the same width, allowing them to better connect with the narrower inner chain link.

Width of the Chain

With the increase in the number of speeds in drivetrains by brands, they have also increased the number of gears. This has led to widening the freehub responsible for holding the cassette in place on the back wheel. The rear wheel has been shifted to the side to accommodate the extra space.

The cassette sprockets have also moved closer and narrower, causing the chains to do the same. These two factors limit the compatibility of the chain with different drivetrains having a different number of gears. An 11-speed drivetrain will require an 11-speed chain.

The width of the chain is compared to the number of gears in the table below.

Width of ChainsNumbers of Gears
13 rear cogs4.9 mm
12 rear cogs5.3 mm
11 rear cogs5.5 mm
10 rear cogs6 mm
9 rear cogs6.5 to 7 mm
6, 7, and 8 rear cogs7 mm

The chains for track or single-speed bikes are usually much more comprehensive when compared to bikes with derailleur gears at typically 9mm. This is primarily done to account for the extra space to cover at the back hub and the much more significant strain the chain undergoes speeding up or slowing down.

Compatibility of the Chain

Previously it was possible to use chains of the same speed from different brands. Reaching modern bikes, the designs are more specific to the brands. SRAM Eagle 12-speed chains are not compatible with road rear derailleurs. While some 11-speed Shimano and SRAM Eagle chains are interchangeable, it leads to a louder drivetrain.

Length of the Chain

When you get a chain, it commonly comes with 110 links which are substantial enough to cover most chain applications. Therefore, a chain must be shortened to fit correctly on the bike. On the other hand, high-pivot mountain bikes need a longer chain, and you might need to join two chains together.

The simplest way to tell how long your chain should be is to look at your old chain, provided it functioned appropriately. Count the number of links in your old chain and replicate the number of links in your new chain. If you’re installing an entirely new powertrain or changing the range of your cassette, you’ll need to be more particular and measure your chain to acquire the proper length.

The most precise technique of sizing a chain for 2-gear and 3-gear drivetrains is to fit the new chain on the cassette’s smallest cog and chainring.

Since you would never ride in this gear, it is the most precise because it estimates the chain’s maximum feasible length. The big-big method comprises winding the uncut chain around the biggest cassette tooth and chainring, ensuring the derailleurs are avoided.

Squeeze the chain’s two ends together securely and add four more links. If you need to cut an outer link and use a quick link, cut the chain at the subsequent accessible rivet.

A long bike chain
The simplest way to tell how long your chain should be is to look at your old chain, provided it functioned appropriately

How to Replace a Bike Chain

  • To replace a bike chain, you will require a chain tool that can work with the particular manufacturer of your chain. The tool will push out one of the chain rivets allowing you to remove the old chain.
  • After proper cleaning and the chain has been sized, it has to be threaded through the drive train, including the back derailleur jockey wheels.
  • You must remove the right amount of links to ensure the proper fit and tightness before the two ends of the chain can be joined.

Reasons for Chain Coming Off and How to Fix Them

Everybody has suffered through a bike chain falling off at one point or another, regardless of if you travel on the road or are a serious mountain biker. There can be a multitude of reasons that can cause this to happen, and we will discuss some of them here and how to deal with them.

  • Dirty Chain

Dirt and grime can build up on the bike chain over time. This can cause the chain to slip, which can end in falling off. Proper chain cleaning and lubrication ensure your bike runs effortlessly and quietly for longer. This can seem like a bother, but it saves you from more significant issues down the line. Use a degreaser and clean your chain as well as the cassette thoroughly.

Cleaning Dirt and grime off a bike chain
Dirt and grime can cause the chain to slip
  • Stiff Link in the Chain

Sometimes a link on the chain can become stiff, not allowing it to move as freely as it needs to work correctly. This can lead to the chain skipping a tooth on the cassette from the rear wheel or the front chain ring, causing it to come off.

To find a link that has gone stiff, place the bike on a stand and shift through the gears slowly with one hand on the derailleur and the other hand feeling for any tight parts on the chain. Once a stiff link is found, use pliers to move it around or use some oil to get the job done.

A stiff bike chain link
A stiff link in the bike chain can cause it to come off
  • Tight or Loose Chain

The length of the chain can cause a multitude of issues. If the chain is too loose, it can easily slip off from the derailleur or the cassette from any pressure or strain. A chain that is too tight can lead to skipping when gears are changed. Chain tensioners can be used to deal with loose chains, and links can be added or replaced for tighter chains.

  • Bent Rear Derailleur Hanger

Regularly riding through rough terrains or forest regions can cause damage to the derailleur hanger. It is a good practice to check if the hanger is in proper shape regularly. The bent rear derailleur hanger will lead to the rear derailleur moving off, which can cause unequal tension on the chain, and the chain will slip off.

You can identify if the hanger is damaged by observing the proper alignment of the pulley wheels of the back cassette. If the wheels are misaligned, you will have to straighten the derailleur hanger, or you may have to replace it with a new one.

  • Derailleur Alignment

Chain slip with every gear chain can indicate that the rear derailleur might be moved out of place. It is essential to check if everything is where it is supposed to be and that the chain is freely moving through the cassette without any obstructions.

For bikes with a double chainring, the front derailleur could also be out of alignment, causing the chain to slip off. There are also chances of the chain getting stuck between the two front chainrings. Adjusting the limit screws of the derailleur could solve some of the problems.

  • Worn Cassette Cogs or Teeth

The teeth on the cassette are the part that allows the chain to grab onto your bike’s drivetrain, which is what lets the entire system work. The teeth or cogs can wear and tear due to overuse or getting attacked by salt, rain, and grime, making the chain slip off the bike. It is better to take the bike to a professional in such a situation as they can service it better or recommend putting on a new cassette.

I found this video useful for finding out whether your cassette cogs/teeth are worn out, and when to replace them:

  • Loose Screws or Bolts on the Drivetrain

One of the most common reasons for the chain slipping off is when the screws on the drivetrain are loose, causing the entire system to go out of alignment. This can easily cause the chain to fall off while the bike is under use. Make sure to use a screwdriver to tighten all the screws of the gear shifting system, which is also known as the derailleur.

  • Shifter Quality

Budget shifters or shifters of a lower quality often end up with the chain slipping off. This is because cheaper shifters cannot maintain equal tension throughout the chain causing it to fall off. You can test out the tension on the chain by pulling on the shifter cable. If there is a loss of tension, the shifters are at fault.

Sadly, the most common fix for this is to get a new shifter, but you can take the bike to a mechanic to inquire about any solutions they might have.

  • Type of Chain

Getting the correct chain type is vital when putting a new one on. If the wrong chain is attached to the drivetrain, it will cause issues fitting with the cassette and derailleur properly, which will end with the chain slipping off. Make sure the chain works with all the parts of your drivetrain when choosing which one to buy.

Bike chain attached to a drivetrain
Attaching the wrong chain to the drivetrain can cause it to fall off
  • Chain Length

This is comparable to an extended chain, but it is generally caused by purchasing the incorrect chain size for the bike. When the chain is excessively long, the derailleur cannot pick up the additional chain length, causing it to drop off easily. The simplest solution is to return the chain to the proper size.

  • Rohloff Hub

While not the most common component of the system, it can still cause issues of chain slipping in the bikes equipped with it. The main advantage of the Rohloff hub is its ability to work with a great range of gears and continue to shift through those gears even under heavy loads. 

It is created with 14 evenly distanced gears, making it easy for the rider to choose the appropriate gear. It is also more durable, requiring little maintenance on top of being water and dirt-resistant.

There could be two main reasons for chain falling in Rohloff hubs. The first is the decrease in chain tension over time. This requires the replacement of the chain or making alterations to get rid of the slack in the case of bottom brackets. 

The second is the worn-out teeth of the rear sprocket or front chainring. These parts will need replacement, or the rear sprocket can be saved in the case of a lucky few.

Here is a summary of the 11 reasons your bike chain keeps falling off when changing gears. Do ensure to refer to the fixes highlighted blue throughout this blog post to resolve them.

11 Reasons Your Chain Keeps Coming Off Your Bike When Changing Gears
Reasons Your Chain Keeps Coming Off When Changing Gears


The last thing you want is for your chain to come undone while riding. Now that we’ve reviewed the eleven most common causes of your bike chain breaking off, we hope you know how to diagnose and repair the problem accurately. Now you can hit the road with renewed confidence to tackle any chain problems!