How To Adjust Your Rear Derailleur on a Mountain Bike

If you’re a mountain biker, then you know that having a properly functioning rear derailleur is crucial. A rear derailleur helps you shift gears smoothly, allowing you to transition from one gear to another while you’re riding. If your rear derailleur isn’t functioning correctly, it can make shifting gears difficult and cause your chain to come off.

To adjust your rear derailleur on a mountain bike, turn the H-limit screw (clockwise or anticlockwise) until the drivetrain doesn’t make noise when pedaling. Then, turn the L-limit screw until there’s no slow shifting. Then, adjust the B screw to fine-tune the tension on the derailleur. 

There are two main types of adjustments that you can make to a rear derailleur: limit adjustments and index adjustments. Limit adjustments help prevent the chain from falling off the gears, and index adjustments help fine-tune the shifting process. We’ll go over both types of adjustments below. 

1. Gather the Necessary Tools

Before you start adjusting your rear derailleur, you’ll need to gather a few tools. You’ll need:

• A Phillips head screwdriver: This will be used to adjust the screws on the derailleur. For starters, get this HXSNEW Magnetic Screwdriver Set from Amazon.com. It comes with high-quality screwdrivers that will make the adjustment process a lot easier, thanks to their ergonomic handles.
• An adjustable wrench: This will be used to loosen and tighten the derailleur’s mounting bolt. Check out this HORUSDY Allen Wrench Set from Amazon.com. It comes with a variety of sizes, so you’re sure to find one that fits the bolt on your derailleur.
• A clean rag: This can be used to wipe away any dirt or grime on the derailleur.
• A repair stand: This isn’t absolutely necessary, but it can be helpful. A repair stand will hold your bike in place while you’re working, making the whole process much more manageable.
• Light lubricant: This will be used to lubricate the chain to ensure smooth shifting.

2. Adjust the H Limit Screw

The H limit screw, sometimes referred to as the high limit screw, is a small screw located on the back of the rear derailleur that regulates how far the derailleur can move. The screw is usually marked with an “H” or a small “+” sign. If it’s not adjusted correctly, you run the risk of overshifting, which can cause severe damage to your drivetrain. 

Therefore, it’s essential to ensure that the H limit screw is appropriately adjusted before making any other adjustments to your rear derailleur. Here’s how to do that:

1. Make sure the bike is on a stand or a level surface.
2. Shift the chain onto the smallest cog and largest chainring.
3. Loosen the bolts that hold the derailleur in place.
4. Pull the derailleur towards the rear wheel until it’s parallel with the spokes.
5. Tighten the bolts that hold the derailleur in place.
6. Shift the chain onto the largest cog and smallest chainring.
7. Look where the chain sits on the derailleur pulley wheel and make a slight adjustment to the H limit screw if needed (turn it clockwise if you need to move it farther away from the frame, turn it anticlockwise if you need to move it closer to the frame). 
8. Test ride your bike and listen for any noise coming from the drivetrain.

Note: If there is excessive noise, go back to step 7 and make another adjustment to the H limit screw.

3. Adjust the Indexing

Once you’ve correctly adjusted the H limit screw, it’s time to move on to indexing. Indexing allows you to fine-tune the shifting process so that your gears are perfectly aligned. If your gears are misaligned, you’ll have difficulty shifting, and your chain may even come off.

There are two ways to adjust the indexing on a rear derailleur: using the barrel adjuster or adjusting the B screw. The barrel adjuster is located on the derailleur itself, and the B screw is on the frame. I’ll describe both but first, let’s start with the barrel adjuster.

4. Adjusting the Indexing With the Barrel Adjuster

The barrel adjuster is a small, cylindrical screw located on the derailleur. It’s used to make minimal adjustments to the derailleur, and it can be helpful if your gears are slightly out of alignment.

To adjust the indexing with the barrel adjuster, follow these steps:

1. First, lubricate the chain and drivetrain.
2. Next, locate the barrel adjuster on your bike. This is a small knob usually found near the shifter or derailleur. 
3. Next, shift your bike into the hardest gear. That will give you the most accurate starting point for adjusting the indexing. 
4. Now, pedaling slowly, shift your bike into the easiest gear. As you do this, observe the derailleur. If the chain moves smoothly and the derailleur is in line with the cogs, then your indexing is already correct, and you don’t need to make any adjustments. If the chain does not move smoothly or the derailleur is not in line with the cogs, you will need to make an adjustment.
5. To adjust the indexing, use a hex wrench to turn the barrel adjuster clockwise if the derailleur moved too far to the left or counterclockwise if it moved too far to the right. 
6. Once you have made your adjustment, pedaling slowly, shift your bike through all the gears to check that they are shifting smoothly and accurately. 

Note: If necessary, repeat steps 3-5 until all of the gears are shifting properly. 

The last thing you’ll need to do is adjust the L-limit screw. The L-limit screw is located on the rear derailleur, and it limits how far the chain can go to the outside (largest cog). This adjustment is necessary because if the chain can travel too far to the outside, it can fall off your bike while you’re riding. 

To adjust the L-limit screw, follow these steps: 

1. First, shift your bike into the largest cog in the back. That will give you plenty of slack in your chain to make the necessary adjustments. 
2. Next, locate the L-limit screw on your rear derailleur. It’s usually located near the top of the derailleur, near the pivot point. 
3. Once you’ve found the L-limit screw, turn it clockwise to tighten it or counterclockwise to loosen it. You’ll want to turn the screw until the chain can barely shift onto the largest cog without falling off. 
4. Once you’ve made your adjustment, test it out by shifting onto the largest cog. The chain should move smoothly and shouldn’t fall off of your bike. If it does, you’ll need to readjust the L-limit screw until the chain stays in place.

5. Adjust the B Screw

If your gears are still not shifting properly after adjusting the barrel adjuster and L-limit screw, you may need to adjust the B screw. The B screw is located on the derailleur hanger (the part of the frame that holds the derailleur in place). 

To adjust the B screw, follow these steps: 

1. Check the chain tension. The first step is to check the tension on your chain. If the chain is too loose, it can cause shifting problems. To check the tension, lift the chain off the smallest cog in the back and pull on it. The chain should have some give, but it shouldn’t be so loose that it can be pulled off by hand. 
2. Close any shift derailleurs and shifters. Next, ensure that all the shift derailleurs and shifters are in the closed position. That will prevent them from accidentally getting bumped out of position while you’re adjusting the B screw. 
3. Loosen the clamp bolt on the rear derailleur cable anchor bolt. Once you’ve confirmed that all shift components are in the correct position, you can start adjusting the B screw. To do this, you’ll need to loosen the clamp bolt on the rear derailleur cable anchor bolt. This bolt is usually located near the rear wheel axle. 
4. Pull the cable tight and tighten the clamp bolt. Once you’ve loosened the clamp bolt, pull the cable tight and then tighten the bolt back down again. Be careful not to overtighten the bolt, as this could damage your bike’s frame or components. 
5. Shift onto the smallest chainring up front and largest cog in back. Now it’s time to test your shift by shifting onto the smallest chainring up front and the largest cog in the back. That combination will give you plenty of slack in your chain, which you’ll need to adjust the B screw properly. 
6. Check that there is enough slack in before proceeding, check to make sure that there is enough slack in your chain so that it can move freely between all of the cogs without binding up. If there isn’t enough slack, you’ll need to loosen up your B screw until there is enough room for your chain to move freely without binding up. 
7. Once you’ve confirmed that there is enough slack in your chain, you can proceed with adjusting your B screw until your shifting is running smoothly again. And if there is not enough slack, loosen the B screw until there is enough room for your chain to move freely without binding up.

Here’s a quick video tutorial if you need a hands-on demo on how to adjust your rear derailleur:

What To Do if You Can’t Get Your Bike To Shift Properly

Now that you know how to adjust your rear derailleur, you should be able to get your bike shifting smoothly again. However, if you’re still having trouble getting your bike to shift correctly, there are a few other things you can try. 

Here are a few tips:

Use the Right Chain Length for Your Bike

If you’re still having trouble getting your bike to shift correctly, one of the first things you should check is your chain length. Your bike’s chain needs to be the correct length to shift properly. If your chain is too long, it can fall off of your bike while you’re riding.

On the other hand, if your chain is too short, it can bind up and prevent your bike from shifting correctly. To find out if your chain is the correct length, you can either measure it yourself or take it to a local bike shop and have them measure it for you. 

Here are a few extra tips for making sure your chain is the correct length: 

• If your bike has a front derailleur, make sure there is enough chain wrapped around the largest cog in the back and the smallest cog up front.
• If your bike doesn’t have a front derailleur, make sure there is enough chain wrapped around the largest cog in the back and the inside of the frame.

Here’s a cool video that may come in handy when determining the right chain length for your bike:

Clean and Lubricate Your Drivetrain

Another thing you can try if you’re having trouble getting your bike to shift appropriately is to clean and lubricate your drivetrain. Over time, dirt and grime can build up on your chain and cogs, preventing your bike from shifting properly.

To clean your drivetrain, you’ll need a bottle of degreaser and a scrub brush. Here are the steps you’ll need to follow: 

1. First, put your bike in a repair stand and remove the wheels. 
2. Next, spray degreaser onto your chain and cogs and let it sit for a few minutes. 
3. After the degreaser has had a chance to break down the dirt and grime, use your scrub brush to remove it from your chain and cogs. 
4. Once you’ve scrubbed away all the dirt and grime, rinse your drivetrain with water to remove any residual degreaser. 
5. Finally, dry your drivetrain with a clean rag and apply a light layer of lubricant to your chain.

Check the Condition of Your Chain

Another thing that can cause shifting problems is a damaged or worn-out chain. If your chain is damaged, it can prevent your bike from shifting correctly.

To check the condition of your chain, look for any bent or broken links. You should also look for any signs of wear, such as stretching or loosening. If you see any of these signs, it’s time to replace your chain. 

You should also check the condition of your cogs and chainrings. If they’re damaged or worn out, they can also cause shifting problems. 

Check for Loose Shifting Cables

Another thing you can check if you’re having trouble shifting is your bike’s shifting cables. Over time, your bike’s shifting cables can stretch and become loose, which can cause your bike to shift improperly. To fix this, you’ll need to adjust the tension on your shifting cables. You can do this by following the instructions in your bike’s manual. 

If you don’t have your bike’s manual, you can usually find it online. Just do a quick search for your bike’s make and model followed by “service manual.” 

Check for Bent or Damaged Components

If your bike’s shifting problems are still not resolved, the next thing you should check is the condition of your bike’s components. In particular, you should check for any bent or damaged derailleurs, chainrings, or cogs.

If any of these components are bent or damaged, they can cause your bike to shift improperly. To fix this, you’ll need to either replace or repair the damaged part. 

Ask a Friend or Visit a Local Bike Shop

If you’re still having trouble adjusting your rear derailleur, ask a friend for help or visit your local bike shop. Sometimes it’s helpful to have another set of eyes to help you spot the problem.

And if you’re still struggling, the folks at your local bike shop should be able to help you out.

Tips for Preventing Future Shifting Problems

Now that you know how to fix shifting problems, you can avoid having them in the future by following these tips: 

• Ensure you regularly clean and lubricate your drivetrain. That will help keep dirt and grime from building up and causing problems. Besides, it’s good bike maintenance.
• Inspect your chain regularly for any damage or wear. If you see any, replace your chain as soon as possible.
• Check your shifting cables for any signs of stretching or looseness. If they’re loose, adjust the tension according to your bike’s manual. 
• Make sure all of your bike’s components are in good condition. If any of them are bent or damaged, replace or repair them as soon as possible. 

Wrap Up

That’s everything you need to know about how to adjust your rear derailleur. By following the steps in this guide, you should be able to fix most shifting problems. But if you’re still having trouble, ask a friend for help or visit your local bike shop.

Remember, the key to preventing shifting problems is regular maintenance. So make sure you clean and lubricate your drivetrain regularly, inspect your chain for damage, and check your shifting cables for any signs of stretching or looseness. By following these tips, you can keep your bike shifting properly without much trouble.