bike cassete why bike chain falling off

12 Reasons Why Your Bike Chain Keeps Falling Off And How To Fix It

You know how frustrating it is if your bike chain keeps coming off. Whether riding alone, with family, or with friends, your bike chain sliding off derails the fun you intend on having.

So, why does this happen, and what are the solutions? Journey with me as I’ll explain 12 reasons why your bike chain falls off and what you should do.

Reason 1: Worn-out Cassette Cog or Teeth

bike cassete why bike chain falling off
Image Credit: Bike Forums

Cogs or teeth enable the bike’s chain to latch on the drivetrain and the entire system to work in unison and perfectly.

However, these teeth-like projections sometimes wear out due to normal wear and tear, rust, the buildup of grime, and lack of maintenance.

The tear and wear may cause the chain to lack a holding place and thus slip off when you pedal. Additionally, this exposes you to danger, especially if you bike on a busy road.

How to Fix

  • One of the best ways to fix this problem is to test if the cassette is worn out. You can use a chain-checking tool to measure the service life. 
  • If the tool shows the cog is worn out, replace it immediately. However, you can prolong its shelf life with proper maintenance.
  • You can also test by replacing the chain with a new one and pedalling hard. If it skips, it is time for a new cassette.
  • If all these methods fail, or you are not technical enough, you can take it to a technician to recommend the best solution, which in most cases is to fix a new cassette.

Reason 2: Hitting Big Bumps

close up bike chain fall off hitting big bumps
Image Credit: Mountain Treads

Sometimes, your bike chain falls off because you hit big bumps. This is especially common if the chain is not tight.

Furthermore, this looseness may be due to loose drivetrain screws and bolts. This leads to the entire drivetrain system shifting every time you go up and down a bump or hit it unexpectedly.

Such situations make riding your bike extremely difficult because you must stop every few minutes to put the bike’s chain back on.

How to Fix

Nevertheless, the solution to this is simple. The best way is to tighten the bolts and screws that hold the drivetrain. 

You can tighten the screws using a specific torque wrench and following these steps

  1. First, ensure the screws and bolts are clean and dry
  2. Insert the wrench and rotate it to tighten it until the bolt and screw feel tight enough.

Reason 3: Low-quality Shifters

close shot bike gear change Low-quality Shifters
Image Credit: Wikimedia

A low-quality gear shifter is another common reason you may have noticed your bike chain fell off. A bike shifter is a device used to control the gear system and select the desired gear ratio. 

If this component is of low quality, your shifting will be problematic, and the chain will keep falling off because the shifter does not match and maintain the desired cable tension after a gear change.

This means the shifter cannot fully help in shifting, or it does not shift the gears entirely

How to Fix

The best way to handle this is to purchase and fix new shifters. The following are the steps on how to replace and fix a gear shifter

  1. Start by twisting the grip off. Use a butter knife to pry the grip from the handlebar’s side. 
  2. Pour water and twist it until it comes off
  3. Remove the shifter assembly by shifting the chain onto the rear or front
  4. Fix the new shifter assembly by sliding it into the handlebar
  5. Reinstall the grips and then adjust the shifter to your desired position

Reason 4: Misaligned Derailleurs

bike chain fell of Misaligned Derailleurs
Image Credit: Reddit

Any misalignment between the derailleur and bike chain will cause the chain to fall off because it will be stretched out, thus causing the gear not to shift smoothly. It can also cause the chain to fall in mid-range due to the problem in the shift. 

Generally, bike derailleurs allow you to change gears on your bike. They’re attached to the front and rear wheels; thus, any wrong alignment affects the gear changes.

Apart from the bike chain coming off, it may cause damage to the entire system.

How to Fix

The following are the steps on how to fix this problem.

  1. Start by shifting the bike’s chain to the smallest cog and biggest chainring
  2. Loosen the cable clamp bolt
  3. Find the low and high adjusters (marked with H and L) and adjust the high gear screw until the jockey pulleys line with the smallest cog

For further guidance, check these helpful videos on how to align misaligned derailleurs.

5. Reason 5: Stiff Chain Link

bike chain Stiff Chain Link
Image Credit: Flickr

A stiff chain link is another reason your bike chain keeps slipping. This results from rust, aggressive and rough gear shifting, and improper installation.

Your bike’s chain link will fall off because when the chain link rotates and reaches the curve area, it will not curve into the cassette, thus sliding off.

How to Fix

This problem has several remedies:

  1. The simplest and basic step is to ensure it is not due to rust. Therefore, the first remedy is to lube your chain frequently
  2. If lubing does not solve the problem, locate the stiff link by back-pedaling the cranck. 
  3. Watch the rear mech, and spot a link that either jumps or clicks as it passes through the jockey wheel.
  4. After spotting the link, use a chain tool and place the link over the one closest to the handle and turn the pin comes into contact with the chain pin and then turn for about an eighth turn
  5. Alternatively, use your hand by holding the link between your hands at a right angle. Twist it severally until it loosens

If all these do not work, purchase a new chain link or have an expert look at your bike.

Reason 6: Dirty Chain

dirty bike chain daytime reason bike chain fell off
Image Credit: Wikimedia

Bikes collect dirt easily, especially when ridden in mud and dusty terrains, and are not washed. The grime and dirt cause the drivetrain to wear out,  links to become stiff, and the bike chain to come off.

The sliding off of the bike chain is due to improper conditions that make the chain, links, and cassette not work optimally. 

Ideally, dirt and grime will prevent smooth movement of the chain in the cogs. Thus, the chain will slip off more easily than move along the cogs, especially on bumpy terrains.

How to Fix

The best way to correct this problem is to regularly clean your bike chain and the moving parts. Some ways to clean these parts include

If there is not much dirt, use a rag and a degreaser, but use bike chain cleaners if it is too dirty.

After the degreaser dies up, apply some lube and wipe off the excess to avoid it attracting more dirt.

Reason 7: Too Long Chain

bike chain fell off reason too long
Image Credit: Reddit

Chains come in different sizes, and it is crucial to pick the right one for your bike. Failure to do this will cause you to select a long chain that does not fit your bike’s length.

This causes your bike chain to slide because the derailleur cannot accommodate the extra length. Thus the chain will slip and fall.

How to Fix

There are two main remedies for this problem. 

  1. If you have purchased the chain recently, try returning it for an exchange.
  2. If returning is impossible, you can take the bike to a pro for link removal.

Reason 8: Too Much Stretched Chain

bike chain Too Much Stretched Chain cause fall off
Image credit: Wikimedia

Over time, your bike’s chain can become elongated because of wear, which causes the bushings’ inner diameter to increase and the pins to groove out.

An elongated chain will often sag and not fit into the cassette cogs and teeth properly, thus slipping off, especially when there is a gear change.

Furthermore, a stretched chain transfers less power when you peddle; hence, you can’t move forward as fast as you wish.

The best and easiest way to know your bike’s chain is stretched or elongated and needs fixing is if you pedal hard and it comes off.

How to Fix

Tighten the chain by following these steps

  1. Using two flat pliers, open the ring connecting the chain and clasp
  2. Remove the clasp and the extra chain links until you get the desired chain length

Reason 9: Loose Screws and Bolts on the Drivetrain

rusty old bike Loose Screws and Bolts on the Drivetrain
Image Credit: Hoffy Cycles

It is common for your drivetrain’s screws and bolts to become loose. This causes the system to shift every time you ride, leading to the chin coming off.

One of the primary reasons for the loose screws and bolts is normal, but sometimes it can be caused by lack of maintenance and rough and bumpy rides.

How to Fix

The best remedy is proper maintenance. This will help to keep the drivetrain in top shape and its right position despite the terrain you are riding in.

Furthermore, you can schedule regular and complete maintenance with an expert who will check all the drivetrain’s components.

Reason 10: An Excessive Chain Angle

bike cassete and chain An Excessive Chain Angle cause bike chain fell
Image Credit:

If your bike chain keeps coming off, it may be because of an excessive chain angle. This happens when riding cross-chained and using a large ring in the back and front or vice versa.

This leads to a slanted chain angle, causing rubbing of the chain and stress on the components resulting in a chain drop.

How to Fix

The best thing about this problem is that it requires proper gear-shifting knowledge. Instead of being aggressive and going for the extreme gears with a sizeable slanting angle, choose and combine intermediate gears.

This will help you have a less chain angle and more options for shifting up or down when necessary.

11. Reason 11: Bent Chainring or Chainring Tooth

Bent Chainring or Chainring Tooth bike chain fell off
Image Credit: Road Cycling UK

A bent chainring or tooth is a major cause for a chain sliding off your bike. Even though it is pretty obvious and easily noticeable, the reasons vary but primarily, it results from accidents.

If your bike strikes a hard surface or gets involved in an accident, your chainring or chainring tooth may get bent enough to cause sliding-off problems.

Several tests can help you determine the bend, such as a simple eye check or placing your hand against it as it rotates. A push against your hand indicates a bent chainring and needs some repair.

How to Fix

It is easy to rectify the bend, such as using a wrench. However, if the damage is extreme, the only solution is to replace it.

Reason 12: Dirty Derailleur

Dirty Derailleur cause bike chain fell off how to fix
Image Credit: Cyclocross Magazine

Like the cassette and a chain, the derailleur can get dirty, too, and cause the chain to fall off. The excess grime and dirt make the chain and tooth fail to connect correctly, leading to the slide-off.

How to Fix

The solution is to clean the derailleur using hot soapy water and a brush together with a degreaser. Here are the steps to follow.

  1. Start by removing the wheel and undoing the derailleur cable. You will achieve this by changing the gears to the smallest sprocket and then opening the quick flip-release system 
  2. Next, unthread the chain to remove the derailleur. Pay attention to the chain’s threading pattern on the derailleur
  3. Loosen the screws of the upper pulley and then pull the chain off the pulley. This leaves the derailleur free, so unscrew the main bolt to remove it
  4. Disassemble the derailleur using the Allen keys set and screwdrivers
  5. Using a brush, scrap off every dirt, or if very dirty first use a screwdriver to scrap off, then put it in a degreaser before cleaning each individually with water and wiping it with a piece of cloth
  6. De-rust and polish your derailleur using a Dremel kit
  7. Assemble the derailleur and fix them back

Also, you can plan for regular cleaning to prevent excessive buildup of dirt in this crucial bike component.


These are some of the reasons why your bike chain keeps coming off. In addition, most of the fixes for slipping bike chains are easy, and there is no need to experience this frustrating experience.

Go ahead now, check and clean your chain and derailleur, and maintain these parts to prevent bike chain falls problems.

Learn 8 reasons why bike chain gets stuck and how to fix it.

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