how to adjust back derailleur on mountain bike

Last Updated on August 23, 2025 by Jaxon Mike

As an avid mountain biker, I know how frustrating it can be when your bike’s rear derailleur isn’t functioning properly. This critical component is responsible for smoothly shifting your gears, and if it’s out of alignment, it can lead to frustrating skipping, chain slippage, and even damage to your drivetrain. Fortunately, adjusting the rear derailleur on a mountain bike is a relatively straightforward process that you can tackle yourself with a bit of know-how.

In this comprehensive guide, I’ll walk you through the step-by-step process of properly adjusting your mountain bike’s rear derailleur. Whether you’re a beginner or an experienced rider, these techniques will have your bike shifting like new in no time. So, let’s dive in and get your rear derailleur dialed in!

Understanding the Rear Derailleur

Before we jump into the adjustment process, it’s important to understand the key components and function of the rear derailleur. This component is responsible for moving the bike’s chain across the rear cog set, allowing you to shift gears and optimize your pedaling efficiency.

The rear derailleur is made up of several essential parts:

• Pulley Wheels: These small, grooved wheels guide the chain as it moves across the rear cog set.
• Outer Plate: The outer plate, or “cage,” houses the pulley wheels and attaches to the derailleur’s pivot bolt.
• Pivot Bolt: This bolt allows the derailleur to pivot and move the chain across the rear cogs.
• Barrel Adjuster: The barrel adjuster is used to fine-tune the tension of the derailleur cable, which controls the derailleur’s movement.

Understanding these key components will help you visualize how the rear derailleur functions and guide you through the adjustment process.

Tools Needed for Adjusting the Rear Derailleur

Before you begin, make sure you have the following tools on hand:

• Bike Repair Stand: While not strictly necessary, a bike repair stand will make the adjustment process much easier and more comfortable.
• Hex Wrenches: You’ll need a set of hex wrenches to loosen and tighten the various bolts on the derailleur.
• Cable Cutter: If you need to replace your derailleur cable, you’ll need a cable cutter to snip the old one.
• Screwdriver: A small flathead screwdriver may come in handy for adjusting the barrel adjuster.

With these tools in hand, you’re ready to begin the derailleur adjustment process.

Step 1: Assess the Derailleur’s Current Condition

Start by closely inspecting your bike’s rear derailleur to identify any obvious issues. Check for the following:

• Bent or Damaged Components: Look for any bent or damaged parts, such as the outer plate, pulleys, or pivot bolt.
• Proper Alignment: Ensure the derailleur is properly aligned with the rear cog set and not skewed to one side.
• Cable Tension: Gently pull on the derailleur cable to check its tension. It should have a small amount of play but not be overly loose.

If you notice any significant issues, such as a bent derailleur hanger or severely worn pulleys, it’s best to have a professional bike mechanic take a look before attempting an adjustment.

Step 2: Adjust the High Limit Screw

The high limit screw is responsible for setting the derailleur’s maximum outward position, which corresponds to the smallest cog on the rear cassette. To adjust the high limit screw:

1. Shift your bike’s rear derailleur to the smallest cog on the cassette.
2. Locate the high limit screw, which is usually marked with an “H” on the derailleur body.
3. Using a hex wrench, turn the high limit screw clockwise until the pulley wheels are just barely aligned with the smallest cog.
4. Shift the derailleur through all the gears to ensure it’s not rubbing against the spokes or frame.

Step 3: Adjust the Low Limit Screw

The low limit screw sets the derailleur’s maximum inward position, corresponding to the largest cog on the rear cassette. Follow these steps to adjust the low limit screw:

1. Shift your bike’s rear derailleur to the largest cog on the cassette.
2. Locate the low limit screw, which is usually marked with an “L” on the derailleur body.
3. Using a hex wrench, turn the low limit screw clockwise until the pulley wheels are just barely aligned with the largest cog.
4. Shift the derailleur through all the gears to ensure it’s not rubbing against the frame or wheel spokes.

Step 4: Adjust the Derailleur Cable Tension

Proper cable tension is essential for ensuring smooth, accurate gear shifting. To adjust the cable tension:

1. Shift your bike’s rear derailleur to the smallest cog on the cassette.
2. Locate the barrel adjuster on the derailleur body or the cable housing.
3. Turn the barrel adjuster clockwise to increase cable tension or counterclockwise to decrease it.
4. Shift through all the gears, making small adjustments to the barrel adjuster until the derailleur is shifting smoothly and precisely.

Remember, it may take a few iterations to get the cable tension just right, so be patient and keep testing your shifts.

Step 5: Fine-Tune the Indexing

Indexing refers to the precise alignment of the derailleur with each rear cog, ensuring a clean, crisp shift between gears. To fine-tune the indexing:

1. Shift your bike’s rear derailleur to the smallest cog on the cassette.
2. Locate the barrel adjuster and turn it clockwise or counterclockwise in small increments until the derailleur is precisely aligned with the smallest cog.
3. Shift through the gears, making additional adjustments to the barrel adjuster as needed to achieve perfect indexing across the entire cassette.

Remember, it may take some trial and error to get the indexing dialed in just right, so be patient and keep testing your shifts.

Conclusion

Adjusting the rear derailleur on your mountain bike may seem daunting at first, but with the right tools and a bit of practice, it’s a skill that every rider should have in their toolkit. By following the steps outlined in this guide, you’ll be able to keep your bike’s shifting performance in top condition, ensuring a smooth, seamless ride on the trails.

Remember, if you encounter any major issues or feel unsure about the adjustment process, it’s always best to consult a professional bike mechanic. They have the expertise and specialized tools to get your bike back in tip-top shape in no time.

Happy riding, and enjoy the fruits of your derailleur adjustment labor!

Frequently Asked Questions

How often should I adjust my rear derailleur?

The frequency of rear derailleur adjustments will depend on a few factors, such as the amount of riding you do, the terrain you ride, and the quality of your bike components. As a general rule, it’s a good idea to check and adjust your derailleur at the start of each riding season, after any major service or repairs, or if you notice any shifting issues. Regular maintenance and adjustments will help keep your bike running smoothly and prevent more serious issues down the line.

What should I do if my derailleur is bent or damaged?

If your rear derailleur is visibly bent or damaged, it’s best to have a professional bike mechanic take a look. Attempting to straighten or repair a severely bent derailleur can be tricky and may cause further damage. In many cases, a bent derailleur will need to be replaced entirely to restore proper shifting performance and protect the rest of your drivetrain.

How do I replace a broken derailleur cable?

Replacing a broken derailleur cable is a relatively straightforward process, but it does require some basic tools and a bit of patience. First, use a cable cutter to snip the old cable at both ends. Next, thread the new cable through the derailleur, making sure it’s routed correctly. Finally, use the barrel adjuster to tension the cable and fine-tune the indexing. If you’re unsure about any part of the process, it’s always a good idea to consult a bike mechanic for assistance.

Can I adjust my derailleur without a repair stand?

While a repair stand can certainly make the derailleur adjustment process easier, it’s not an absolute necessity. You can still adjust your rear derailleur without a stand, but you may need to get creative with how you support and position your bike. One option is to flip your bike over and rest it on the handlebars and saddle. Just be careful to avoid any damage to the components during the adjustment process.

How do I know if my derailleur needs to be replaced?

There are a few telltale signs that it may be time to replace your rear derailleur. If the pulleys are severely worn or the derailleur body is cracked or bent beyond repair, replacement is likely the best course of action. Additionally, if you’re having persistent shifting issues that can’t be resolved through basic adjustments, a worn-out derailleur may be the culprit. Consult a bike mechanic if you’re unsure, as they can assess the condition of your derailleur and recommend the best course of action.