How to Tighten a Mountain Bike Chain Derailleur Step by Step

The mountain bike chain derailleur is one of the most important and hardest working components of your bike. It plays a vital role in ensuring that you have an enjoyable cycling experience. Unfortunately, most bike riders often ignore this important bike component. When some parts of the derailleur like the bolts and nuts become loose, the full performance of other parts of the bike like the chain and gears can be affected and the chain could fall off the cog while switching gears. Fortunately, knowing how to tighten a mountain bike chain derailleur can quickly solve this problem. 

To tighten a mountain bike chain derailleur, first, identify the loose screws on the derailleur and at the hanger mount. Tighten the hanger bolts until the derailleur is firmly secured. The H-screw on the derailleur adjusts the outermost limit of the derailleur, and the L-screw adjusts the inner limit.

You may need to tighten a mountain bike chain derailleur if your chain keeps falling off or if you struggle to select the gear that you need to be in.
When the chain constantly falls off or gear selection is inaccurate, this could indicate that the derailleur needs to be tightened or adjusted. Image Source: Amazon.

You might also find interest in learning how to stop a mountain bike chain rubbing the front derailleur. If so, check out our related article for more information.

What is a Derailleur?

A derailleur is a device that allows you to change gears by shifting the bike’s chain from one sprocket to another. A derailleur receives its signal to move the chain onto a different sprocket when the rider makes a gear change on the shifter which alters the tension in the gear cable.  

The main function of the derailleur is to guide the chain onto larger or smaller sprockets during gear shifts. 

As this article from the International Research Journal of Engineering and Technology explains, this innovative development in bicycles makes it possible for the rider to select a gear that is appropriate for the terrain that you are riding on.

There are usually two types of derailleurs—one at the front known as the front derailleur, and another at the rear known as the rear derailleur. The front derailleur is located directly above the largest front sprocket. The front derailleur ‌makes it possible for the chains to shift from chainring to chainring, thus allowing you to switch gears quickly and easily. The rear derailleur is located below the rear cassette and is attached to the bike by a bracket. It performs two main functions—keeping the chain taut and switching the gears. Our article that outlines quick and proper mountain bike chain maintenance explains how to take care of the derailleur and the rest of the drivetrain.

If the rear derailleur is loose, it will affect the mountain bike chain’s tension negatively and should be tightened.
The rear derailleur is located below the cassette and keeps the chain tension constant. Image Source:

Types of Rear Derailleurs

Before you tighten a mountain bike chain derailleur, you need to learn a bit more about the different types. The rear derailleurs usually come in 3 different sizes or types.

The three types of rear derailleurs are long cage rear derailleurs, medium cage derailleurs, and short cage derailleurs. 

Long Cage Rear Derailleurs

Long cage rear derailleurs like this are SGS derailleurs that have a chain range capacity of 44-43T and are mostly used for bikes that have 27 or 30 gear combinations, and can also conveniently work with bikes that have a much wider gear range. As this extract from Effective Cycling explains, affording the rider wider gear ranges ensures the rider has more options when it comes to selecting the correct gear for the terrain.

A unique advantage of the long cage gear combination is that it can support any chain tension regardless of the choice of gears. Though this derailleur may work with all gear ratios, the chain may occasionally become slack and hit the bike frame. The long cage derailleurs are commonly used for mountain bike riding and for cross-country race competitions. 

A long cage derailleur is suitable for a mountain bike that has 27 - 30 gear combinations.
A long cage derailleur offers a wider gear range. Image Source: Amazon.

Medium Cage Rear Derailleurs

Medium cage rear derailleurs like these are GS derailleurs and they have a chain range capacity of 37-39T. They are mostly used for mountain bikes that have 28 to 36 teeth and are often used for in-between road drivetrains. With the medium cage rear derailleurs, the chains are less likely to be hit by rocks, but they may often not be as taut as you would want them to be.

Medium cage derailleurs have a chain range capacity of 37-39T.
 A medium cage derailleur is less likely to bump into roots and rocks. Image Source: Amazon.

Short Cage Rear Derailleurs

Short cage rear derailleurs like these are SS derailleurs and they have a maximum chain capacity of 33T or less. They have the advantage of providing better tension and they allow shifting of gears to be done accurately and silently. They are also less susceptible to damage. 

However, short cage derailleurs should not be used with bikes with a 27-gear ratio, because the chain tension won’t remain constant and the chain could drop off the gears. Our article that explains how to tighten a mountain bike chain that is too loose offers handy tips on how to fix a dropping chain.                

A short cage derailleur has better tension and allows for accurate and silent gear changing.
A short cage derailleur is not suitable for use on a mountain bike with a 27-gear ratio. Image Source: Amazon.

Here is a summary of the three types of rear derailleurs:

Type of Rear Derailleur Gear Range  Example From Amazon
Long cage rear derailleur Wide gear range Sram Mtb gx type 2.1 
Medium cage rear derailleur Moderate gear range Inkesky rd-tz31-gs 6/7 
Short cage rear derailleur Small gear range Shimano 105 rd-5701-ss

You might also be interested in learning how to fix a mountain bike chain. If so, be sure to read our related article for more information.

How Do Mountain Bike Derailleurs Work?

Both the front and rear derailleurs move the chain across the cassette onto the various cogs as the gears are selected. 

While pedaling, the derailleurs push the chain to a higher and lower sprocket. This pushing action of the derailleur is aided by special teeth-shaped structures known as shift ramps. The shift ramps are indents on the large ring that grab the chain plates and position the chain on the chainrings. 

As the excerpt from Cycling Science explains, the gear shifter adjusts the tension in the gear cable so that the jockey pulley and idler pulley pivot to change the chain position on the cassette.

Structure of the Rear Derailleur

The rear derailleur is usually located below the rear cassette and they are normally attached to the bike by a bracket. It also has a spring-loaded linkage known as the “parallelogram” which is connected to a cage housing two pulleys that pivot up and down. The upward pulley is known as the jockey pulley, its function is to drive the chain into the sprockets. The lower pulley is known as the idler pulley and it ensures that the chain is tight between the sprockets.

The lower pulley of the derailleur ensures that the mountain bike chain stays tight.
 A rear derailleur is made up of different components that work together. Image Source: Pinterest.

How Does the Rear Derailleur Work?

The entire working process of the rear derailleur is made possible by means of a cable that is connected to a trigger or lever on the gear shifter, located on the handlebars. The cable will usually be tightened or slackened whenever the lever is pressed. This action will normally make the parallelogram in the derailleur bend, moving the cage with it. 

As the cage moves, the guide pulley is brought directly below the sprocket, and it is pivoted around the point where it is mounted in order to allow for the increasing or decreasing chain slack. This user manual from Shimano explains how to determine the correct chain length for a 10-speed Shimano derailleur like this

When the bike is ridden at a higher gear, the derailleur moves outward and inward causing the chain to move outward onto the smaller sprockets. The resultant effect of this action is that the chain will eventually become slack, but this slackened effect of the chain is adjusted by the tensioner pulley. When the bike is ridden at a lower gear, the derailleur will move inward and outward causing the chain to move inward onto the bigger sprockets. The resultant effect of this action is that the chain is tightened.

Structure Of The Front Derailleur

A front derailleur like this generally has fewer parts and a simpler structure. It is located directly above the largest sprocket and is made up of a cage that is connected directly to the links in the parallelogram. Its function is to guide the chain as it rises or descends through various chainrings.

The front derailleur guides the chain as it rises or descends through various chainrings.
A front derailleur generally has fewer parts than a rear derailleur. Image Source:

How Does the Front Derailleur Work?

The working principle of the front derailleur is very similar to that of the rear derailleur. When pedaling, there can be both inward and outward movements. During outward shifting, the chain bends and rises because of the pedaling. But modern chainrings have features like the shift ramps which enable the chain to be picked as it moves outward. Inward shifting also occurs in a similar manner to outward shifting. 

There are limited screws on the front derailleur which can also be found on the rear derailleurs. The ‘‘H’’ and ‘‘L’’ screws are used to stop the cage whenever it travels to the extreme ends. Both screws determine the outermost cage travel and innermost cage travel, respectively. There are also shifter levers attached to shifter cables which control the movement of the front derailleurs.

How to  Tighten a Mountain Bike Chain Derailleur Without Removing It

When the screws of the mountain bike chain derailleur are loose, riding is usually very annoying and problematic as there would be several issues ranging from the chains dropping off the cog to the gears being badly indexed. Minute adjustments on the derailleur screws will tighten it securely. 

To tighten the MTB chain derailleur without removing it, first, choose compatible hex keys that fit the derailleur mounting bolt and jockey wheel. Shift the chain onto the smallest sprocket and ensure the B-tension screw is behind the hanger stop. Tighten loose bolts and nuts starting with the derailleur mounting bolts.

Tools Needed to Tighten a Mountain Bike Chain Derailleur

Here we have a summary of all the tools that you will need to tighten a mountain bike derailleur:

Tool Needed To Tighten A Mountain Bike Chain Derailleur Why It Is Needed Example From Amazon
Chain Pliers Are used for cutting and twisting wires, and also to loosen and tighten bolts Satco 90-099 chain pliers
Chain Binders Are used to tighten a chain when a load is to be secured for transportation Dc cargo mall chain binder
Pedal Wrench Is used to unscrew pedal from the crank arm Park tool Pw-3 pedal wrench
Derailleur Alignment Gauge (DAG-2.2) Is used to straighten misaligned derailleur hangers, and to solve other problems related to shifting Park tool Dag-2.2 derailleur hanger alignment gauge
Screw Drivers Are used to insert and remove screws Spec Ops multi-bit screwdriver
Allen Wrench (Hex Key) Are used to loosen and tighten hexagonal screws and bolts Mulwark 17pcs folding Allen wrench

To make sure that you have the right tools on hand to work on your mountain bike, check out our ultimate list of tools for mountain bike maintenance. Similarly, you might be interested in learning about the most common mountain bike problems. Be sure to read our related article for more details.

Here is the step-by-step process of tightening a loose mountain bike chain derailleur:

Step 1. Set the Screws Limit

Disconnect the gear cable and gently turn the pedal forward until the chain‌ drops to the smallest sprocket. Checking the back of the derailleur, locate the H screw. This screw determines the higher limit of the derailleur—that is, how far towards the frame the derailleur will be able to move. Ensure that the uppermost jockey wheel is placed directly below the smallest sprockets.

Step 2. Tighten the Cable

Select the highest gear which selects the largest cog, and then turn the barrel adjuster from right to left until it gets to a level where it is tight. Then pull the cable on the derailleur as tight as possible using the cable anchor to attach it to the body of the bike. Once you’re done with this, select the third gear on the shifter, and pedal forward to shift the chain. Check if the jockey wheel falls below the third sprocket. If it does, then you’re doing it right.

Step 3. Adjust the Cable Tension

The barrel adjuster is used to regulate the tension of the cable. When you turn it in an anti-clockwise direction, the tension in the cable is increased. When it is turned clockwise, the tension decreases. If the chain does not shift up, turn the barrel adjuster anti-clockwise. If there is a skipping of gears, turn the barrel adjuster clockwise to decrease the tension in the cable. If the drivetrain is relatively silent, then the cable tension has been properly set

Step 4. Shift the Derailleur Up

Below the H screw is another screw marked L, the L screw determines the lower limit. Push the derailleur close to the wheel, then turn the screw clockwise until the derailleur cannot move beyond this ‌point. This is important in order to prevent the derailleur from getting tangled in the spokes.

Step 5. Turn the B-tension Screw

Now it’s time to adjust the B-tension screw which is located on the upper part of the derailleur. Turn the B screw clockwise in order to move the jockey wheel away from the cassette then twist the B screw until the gap is approximately 3mm.

Using an Allen key, adjust the screws on the rear mountain bike derailleur to make sure it has enough tension and is tight enough.
Use a hex key to turn the screws on the rear derailleur to tighten it. Image Source:

You might also find interest in learning when to replace a mountain bike chain or how to untangle a mountain bike chain. Make sure to read our related articles to find out more.

How to Adjust a Rear Derailleur on Mountain Bike

Adjusting the rear derailleur could make all the difference to the way your chain moves and shifts through the various gears.

To tighten a mountain bike's rear derailleur, gather a small Philips screwdriver, an Allen wrench, and a light lubricant. Locate the high limit screw, the low limit screw, and the B-screw and adjust them all to make sure the chain and derailleur are working smoothly. 

This video tutorial by Park Tool explains exactly how to adjust your rear derailleur. And in case you need to adjust something on your mountain bike while you are out riding on a trail have a look at our tips on how to choose a mountain bag that locks so that you know your tools will be safe.

Step 1. Locate the High Limit Screw

The high limit screw controls how much distance the derailleur will be able to shift the chain off the smallest cog. Shift into the smallest cog, twist the screw out a few turns, then thread the screw in until the clicking noise (which is produced when the chain is shifting off the cog) goes away.

Step 2. Locate the Low Limit Screw

The low limit screw controls how much distance the derailleur will have to shift off the biggest cog. Shift into the biggest cog, twist the screws out a few turns, then thread the screw until pedaling is smooth.

Step 3. Bring the Top Derailleur Pulley Close to the Cassette Cogs

Bring the top derailleur pulley closer to the cassette cogs, but don’t bring it so close that they rub each other. Make sure they are a moderate distance from each other but don’t allow them to be too far as this will result in sloppy gear shifting. Next, locate the B-tension screw, and thread it in and out in order to adjust the top derailleur pulley.

Step 4. Check the Tension of the Cable

Cycle and try shifting through the various gears. If the cable tension is too low, unthread the barrel adjuster which is found on the shifter by twisting it in an anti-clockwise direction. If the cable tension is too tight, thread the barrel adjuster in a clockwise direction.

What Screws are Needed to Adjust a Derailleur?

Most derailleurs are usually made up of three limit screws—the lower limit screws, the upper limit screws, and the B-limit screws. These screws play very important roles in the adjustment of the derailleurs.

To adjust the derailleur, there are three screws to use; the B limit screw for controlling the gap between the derailleur upper pulley and the bottom cogs, the upper screw for setting the maximum distance a derailleur should shift in high gears, and a lower screw for setting the maximum distance a derailleur should shift in the lower gears.

Derailleur Limit Screws Function
B-Limit It controls the gap between the guide pulleys and the bottom of the cogs
Upper-limit Screw It controls the maximum distance the derailleur can move in high gears
Lower-limit Screw It controls the maximum distance the derailleur can move in low gears
The various crews on the rear derailleur can be adjusted to tighten or loosen the mountain bike chain tension to make gear changing easier and smoother.
Higher limit and lower limit screws control the derailleur’s alignment in high and low gears.  Image Source:

Related articles:

A step-by-step guide on how to replace a mountain bike chainring

Is a mountain bike chain guide worth it?

Methods to Resolve Rear Derailleur Tension Problems 

For proper shifting, your bike cables need to have the right amount of cable tension. But different factors could make your bike derailleur cable not have the right amount of tension. When this happens, shifting in your bike would be poor or sluggish. To tighten a mountain bike chain derailleur, you need to resolve these tension issues.

To resolve the rear derailleur tension problem, check the return tension spring hole in the derailleur if it’s loose, adjust the rear derailleur cable, tune the barrel adjuster to achieve the right tension, and realign the derailleur properly on the derailleur hanger.

Our article that discusses how to fix mountain bike grip shifters will help you determine if your gear shifting problems are cable-related or derailleur-related. And if you find that the problem is the shifters we explain how to remove mountain bike gear shifters so that they can be repaired.

We suggest that you follow these steps to sort out your gear shifting issues:

1. Tune the Barrel Adjuster Until the Right Cable Tension is Achieved

The barrel adjusters are serrated knobs that are specifically designed to control cable tension. 

Turn the barrel adjuster anti-clockwise to increase the tension on the cable. This helps the rear derailleur shift towards the spokes. Conversely, turning the barrel adjuster clockwise decreases the tension and brings the rear derailleur closer to the spokes.

To tighten the cable tension of your mountain bike turn the barrel adjuster.
To adjust the cable tension, turn the barrel adjuster. Image Source: i-stack.

2. Properly Realign the Rear Derailleur With the Derailleur Hanger 

The derailleur hanger is the point at which the derailleur comes in contact with your bike. The derailleur hanger should not be bent and should be in a perpendicular position relative to your rear wheel. A realignment tool like this DAG-2.2 can be used for realigning the derailleur hanger. 

Using the realigning tool, check for realignment in the 9 o’clock and 3 o’clock positions (for horizontal alignment) and at the 12 o’clock and 6 o’clock positions (for vertical alignment.) Rotate the arm of the alignment tool and ensure the hanger is aligned within 4mm both vertically and horizontally.

Using a realignment tool make sure that the derailleur hanger and the derailleur are properly aligned.
The DAG-2.2 realignment tool can be used to properly realign the derailleur hanger with the rear derailleur. Image source: Amazon.

3. Change the Derailleur Tension Spring Hole 

Derailleurs usually have two or more holes with springs inside these holes. The springs found in each hole are usually relaxed. Removing a spring found in a given hole and putting it in another hole will usually change the tension of the derailleur. So, if the tension of the derailleurs is not ideal this can be fixed by removing the spring from one hole and putting it in another.

The tension of the derailleur can be changed by removing a tension spring from one opening and putting it into another.
The derailleur tension can be changed by changing the tension springs in the derailleur holes. Image source: Bikestackexchange.

4. Adjust the Rear Derailleur Cable

Locate the high limit screw and low limit screw, and shift them close to the smallest and biggest cogs, respectively. Then set the top derailleur and the cassette cogs at a moderate distance apart from each other. Turning the B-tension screw thread in, cycle the bike through different gears. Observe the tension on the cable—threading and unthreading the barrel adjuster will regulate the tension in the cable and properly adjust it in case the cable tension is too high or too low.

When adjusting the screws of the derailleur, shift through the gears of the bike and make sure that the tension is suitable.
Observing the rear derailleur cable, make the necessary adjustment until the cable tension is fine. Image source:

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