What Causes Mountain Bike Chains to Fall Off? (Explained)

What Causes Mountain Bike Chains to Fall Off

Although mountain bikes may have a lot of similarities with other bicycles, they are built with unique enhanced features to optimize their performance and durability. One of these enhanced features is the mountain bike chain. Mountain bikes usually come with heavy duty chains because of the intense scenarios and environments they are going to operate in.

There are several reasons that can cause this:

  • A worn-out drive train
  • A stiff link in the chain
  • A worn-out chain
  • Wrong chain size
  • Incompatible chain
  • The chain is clogged
  • Bent chainring
  • Derailleur problems

That being said, this article takes a look at some of the common causes of this problem, how you can solve it, along with some additional information on how to care for your mountain bike’s chain.

Reasons Your Mountain Bike Chain Keeps Coming Off

A Worn-out Drive Train

The drive train of your bicycle is made up of all the parts that you use to move the bike. Some of the drive train’s components are the pedals, cranks, chainrings, the chain, cogs and the derailleur (the device that changes the gears). A tell-tale sign of a worn-out drive train is worn out teeth on the cogs. If the teeth start to look like shark teeth, a replacement is due.

If you’ve ridden your bicycle for more than a thousand miles, it would also be a good time to replace the drive-train.


Your chain can come off when your bike experiences high impact. This could happen when you make a big drop, hit a big bump or crash.

A Stiff Link in the Chain

A single stiff link is all it takes to pop your chain off. Stiff links cause bike mishaps which could later lead to accidents since it doesn’t easily bend around the chainring and the jockey wheel.

This problem can be fixed by oiling the chain. If that doesn’t fix the problem, there’s no need to worry. You can backpedal the chain as you watch the rear derailleur while looking out for a link that jumps and clicks as it passes over the jockey wheel. That would be your stiff link. You can loosen it using a chain tool or you can try bending it side to side by hand. Be sure to use gloves as you do this to protect your hands.

A Worn-out Chain

As you ride your bicycle, the chain keeps elongating. This is because the internal components of the chain have started to wear down. You can easily check for chain elongation using a tool called a chain checker. Most chain checkers assess 0 to 1% of wear on your chain. There are a few pointers to help you decide whether you should get your chain replaced depending on the results from using the tool and the number of rear gears.

  • 0.5%- if you have more than 11 rear gears, you should replace your chain.
  • 0.75%- if your bike has 10 or fewer gears you should change your chain.
  • 1% or higher- you should replace your chain if you have a single-speed or a two-sprocket bike.

Wrong Chain Size

If you recently replaced your chain and it keeps dropping, chances are the new chain you got is too long for your bike. You can check for your chain size by comparing it with the old one. It should be slightly shorter than the old chain since the old one has stretched over time.

To get the proper chain length, you might have to take out a few chain links. A properly sized chain should reach the large-large gear combination, and the rear derailleur shouldn’t overlap itself while in the small-small gear combination.

Incompatible Chain

If your bike isn’t a single speed, then it uses a derailleur bike chain. These chains are designed to allow the transition between sprockets as you shift gears. As a result, the chains are made for use with specific drivetrains. If your chain keeps coming off, you might want to counter check the compatibility of your chain with the drivetrain.

You can also look at the manufacturer’s instructions to see if your drivetrain can be used with other brand chains.

The Chain is Clogged

As you ride your bicycle, dirt makes its way into the chain components. As a result, your chain may not move smoothly in the cogs and this might cause it to fall off, especially as you ride along bumpy trails.

You should frequently oil and clean your chain. Going at it with a degreaser and clean rags and re-oiling the chain will make it as good as new.

Bent Chainring

A bent chainring or even one chainring tooth could cause your chain to keep falling off. This is usually caused by accidents. To see if your chainring is bent, you can place your hand against the frame as you gently push something into the chain. If you feel some resistance against your hand, this means the ring is bent.

You can fix this problem by bending the chainring back using a wrench or using a chain straightening tool. An alternative would be to replace the chainring altogether.

Derailleur Problems

The derailleur is the part of your bike responsible for changing gears. Some mishaps can occur here which might cause your chain to drop.

The derailleur is dirty

A dirty derailleur will not work optimally, and this might affect the chain also. You can clean your derailleur using a brush coated in a degreaser. Afterward, use hot soapy water to get rid of any remaining dirt, and finish with a freshwater rinse.

Misaligned rear derailleur

If the misalignment is extreme, the chain might drop since the limit screws will restrict the chain’s movement into the spokes. This case can also cause noisy gear shifts.

Bent derailleur hanger

A proper hanger should be parallel to the cogs. It should not bend inwards or outwards. If this is the case, you can bend it back to shape using a wrench. This is a fairly delicate procedure as the hanger could break.

Failed clutch

Clutches are present to help reduce the tension in the rear derailleur and prevent the chain from bouncing. If the chain tension keeps giving you problems, the clutch might be a reason why. Some manufacturers cover this component in the warranty, and it can be replaced for free. If that isn’t an option, you can always take it to your local shop.

Shifted front derailleur

If your bike has a 1X drive system, you can rule out this as a cause for your chain falling off since this type doesn’t have a rear derailleur, to begin with. If it has one though, the first step would be to check the cage height. The ideal cage height should be 2-3mm above the teeth on the largest chainring. If the cage is too high it would give the chain room to fall off as you change gears. Lower cage heights would run into the larger chainring.

If this isn’t the case, you might want to take a look at the angle of the cage. If it is misaligned, the chain might twist, causing it to drop. The cage should be parallel to the chainring.

If none of these seem to be the matter, there are some other items you can check to see what the problem might be.

  • Check that the rear wheel is not loose.
  • Check if the cassette is loose.
  • Confirm that the chainring bolts are tight.

Ways to Keep Your Mountain Bicycle Chain Lasting Longer

A bike chain typically lasts from 500 to 5,000 miles, depending on how often you ride a bike and the type of chain you own. Here are a few tips you can use to ensure that you get the most wear out of your bike chain.

1. Oil Your Chain

You should frequently lubricate your chain to make sure everything runs smoothly. This doesn’t mean that you should go overboard with the lube. Pay close attention to your drive-train, and if things sound dry and squeaky, your chain needs to be oiled.

After lubing your chain, be sure to wipe away any excess. Do not use motor oil to lube your chain- motor oil has acids and metal particles that can weaken your chain and cause it to wear faster. If you live in a relatively wet area, you should use a wet lube to prevent your chain from getting rust.

2. Frequent Cleaning

Your bicycle chain is likely to pick up dirt and grime as you ride it. To keep the chain in prime condition, you need to clean it often. There are some ways to make sure your chain stays clean. You can use a degreaser and a clean cloth to wipe your chain. You can also use a nylon brush, warm water ad some liquid soap to scrub down the chain.

If you feel like the chain is too dirty, you can take your bike to your local shop for a thorough wash. An alternative would be to take off the chain and shake it around in a bottle filled with a degreaser. Remember to dry and lube your chain after every wash.

3. Your Riding Style

Your chain’s lifespan is also affected by the way you ride your bicycle. Riding at a high speed is more efficient and cuts down on the cost. Also, pedaling at a rough gear stresses the chain, which affects its service life.

4. Avoid Cross-chaining

Cross-chaining is the practice of using the small chainring and small cog in the rear, or the large chainring and large cog in the rear. This causes an extremely slanted chain angle, that stresses the hardware and causes chain rub that causes your chain to drop.

5. Replace Worn Out Drive-train Components

You should replace your chainring and other components often so that they don’t wear out the chain. When these parts are worn out, the teeth will start to look round, which will cause your chain to start skipping gears.

Are All Mountain Bike Chains the Same?

There are 2 basic types of bicycle chains, one-speed chains, and derailleur chains. One-speed chains are designed for bikes with one sprocket on the crank-set and the second sprocket on the wheel. These chains are not designed to function on multiple-gear derailleur bikes. Mountain bikes use derailleur chains, which are designed to move from one sprocket to the other.

Bicycle chains can be grouped into three types with respect to the chainlinks: regular, hollow-pin, and half-link.

  • Regular chains are most common, and they can be found on almost every mountain bike. They provide strength and efficiency, but they are not optimized for any function.
  • The hollow-pin chain is so-called because it uses hollow steel pins in every link. This concept makes the chains lighter without affecting their functionality.
  • For the half-link chain, every link that makes it is identical. The links all have one small end and a larger one that fit into each other. This chain type is used with single speed bikes in order to get optimal chain tension.

Mountain bike chains can also be grouped by their sizes. The size is dependent on the number of gears in your drive-train. There is the 10 speed, 9 speed, 6/7/8 speed, and the single-speed specific chain.

Most chains are made out of steel

How Tight Should a Bike Chain Be?

If your bike chain is too loose, the chain will keep coming off as you ride. If the chain is too tight, its chances of snapping are higher, and this could cause accidents.

Your chain should only allow you to move it up and down one inch. If it sags, it means you need to tighten the chain. If you tighten the chain and it still feels loose, this is a sign that the chain is stretched and needs replacement.

Does Chain Length Affect Speed?

For a mountain bike, chain length has a lot to do with the bike’s speed. If the chain is too long, it might cause floppiness and slacking which will, in turn, affect the gear combination and cause your bike to move slower. If the chain is too short, it may jam between the derailleur system due to too much tension.

With a short chain, you also won’t be able to shift into the large-large gear combination and trying to might cause your chain to break in half.

How Much is a Chain for a Mountain Bike?

How much the chain costs depends on the brand, quality, and the type of bike you’re buying a chain for. A chain for a cheaper bike retails at around $15 to $50, and higher quality chains for higher quality bicycles cost between $50 to $200.

Higher quality chains are more expensive since they are thinner, lighter, more durable and more resistant to corrosion.

How Often Should I Change My Bike Chain?

On average, a mountain bike chain should be able to serve you for 500 to 6,000 miles, but some factors may affect the lifespan of your bike’s chain. The conditions in which you ride, the care you give to your drive-train, and how much power goes through it all affect how long your chain lasts.

It is important to replace your chain as soon as you notice signs of wear since a worn-out chain also increases the wear on other bike components like the chainrings and the cassette.

Some pretty obvious signs tell you when your chain needs replacement. If the chain is snapped, a link is bent out of shape or the gears start slipping, it’s a good time to get another chain.

There are also some tests you can run to see if your bicycle chain is still in good shape. There are special tools that test the wear on your chain by measuring the distance between the chainlinks. If this tool is inaccessible, you can test the chain by flexing the bottom section of the chain from side to side. If the chain flexes and the links are loose and ratty, this could also be a sign that the chain has reached the end of its line.

In case you can’t tell if your chain needs a replacement, you can always take the bike to your local repair shop for a quick check.

Is My MTB Chain Too Long?

Your chain length is too long if you notice some slack when it is in the small-small combination. Your chain should be able to keep the derailleur under tension without being locked out.

There is a method you can use to tell whether the chain length is okay for your bicycle. There are chain length calculators that can help you choose the most appropriate chain length.

There is no need to worry if you can’t access a chain length calculator. You can find the perfect length by running the chain around the two largest cogwheels- the fastest at the front and the slowest at the back- without passing it through the derailleurs.

Once you get this length, add one inch and a complete inner and outer link. This chain length should be perfect for your bike.

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