Perfecting Your Bike's Shifting: A Step-by-Step Guide to Rear Derailleur Adjustment

Table of Contents

• Introduction to Rear Derailleur Adjustment
• Setting the H Limit Screw
• Indexing: Aligning the Guide Pulley with the Cogs
• Adjusting the L Limit Screw
• Checking and Adjusting the B Screw
• Final Checks and Troubleshooting

Introduction to Rear Derailleur Adjustment

Adjusting the rear derailleur is a crucial task for ensuring optimal shifting performance and a smooth riding experience. Most cyclists face shifting issues at some point, whether it's the chain not reaching all gears or making noises during shifting. This guide aims to help you understand the components involved in rear derailleur adjustment and walk you through the step-by-step procedures to fine-tune your shifting.

Before we begin, let's take a quick look at the components and procedures involved. The rear derailleur is a mechanism that shifts the chain across the rear cogs. It is connected to the shifter by a cable that runs through a housing. Most bikes use an index shifter that moves the cable in predetermined increments with each click. Inside the derailleur body, there is a spring that constantly pulls the derailleur outward, and the cable holds against this spring in various shift positions.

Components and Procedures Overview

Derailleurs are fitted with limit screws that prevent the derailleur from moving too far inward or outward. These limit screws stop the linkage at each end, preventing the chain from going into the spokes or the frame. The first step in our adjustment process will be to set the H limit screw, followed by indexing the derailleur. Indexing is the process of aligning the guide pulley with the cogs, ensuring that each shift lines up with each cog. The barrel adjuster, located on the derailleur or the shifter, allows us to fine-tune the shift increments. After indexing, we'll adjust the L limit screw and check the B screw adjustment, which controls the spacing between the guide pulley and the cogs.

Setting the H Limit Screw

The H limit screw controls the inward movement of the derailleur, preventing it from shifting the chain too far inward and into the spokes or frame. Our goal is to dial in the H limit screw as close as possible to the inward cog.

Begin by visually checking the derailleur hanger for any signs of bending. If it's clearly bent, the adjustments may not work correctly, and you should consider aligning the hanger (refer to our video on hanger alignment for more information).

If your bike has multiple front chainrings, shift the front derailleur to the largest ring. For the rear, shift to the smallest cog and keep clicking until there are no more clicks. This ensures that the shifter is fully actuated outward.

Indexing: Aligning the Guide Pulley with the Cogs

Indexing is the process of lining up the guide pulley with the cogs, ensuring that each incremental shift lines up with each cog. The barrel adjuster allows us to make these adjustments.

If your bike has two front chainrings, stay on the largest front chainring. If it has three front chainrings, shift to the middle one. On the rear, start on the smallest cog. Pedal at a normal riding cadence and shift the rear lever one click - no more than one click. Some shifters are designed to click multiple times with a single lever push, so push the lever slightly until you hear one click.

If the chain does not shift to the next gear, return the shift lever to the outermost click and turn the barrel adjuster one full turn counterclockwise. Try the shift again and repeat until the chain shifts to the next gear. If you have unthreaded the barrel adjuster too much, thread it back in fully and then out one or two turns. Make sure you're on the furthest outward shift position and the smallest cog, then remove any slack from the cable at the pinch bolt.

Adjusting the L Limit Screw

The L limit screw controls the outward movement of the derailleur, preventing it from shifting the chain past the largest cog and into the spokes. Similar to the H limit screw adjustment, we'll purposely make the L screw too tight and then back it out slightly until it's just right.

Shift the chain to the next-to-largest chainring in front and the second-largest cog in the rear. Shift to the largest cog to determine if the L screw is already too tight. If the chain does not make the shift, the L screw is already too tight, which is what we want. If there's excessive noise once on the largest cog, the L screw is also too tight.

If the shift is acceptable with no excessive noise, the L screw is not too tight. In this case, turn the derailleur one click outward, tighten the L screw a half a turn, and try the shift again. Repeat until there are symptoms of the L screw being too tight.

Checking and Adjusting the B Screw

Most derailleurs have an adjustment for the spacing of the guide pulley to the cogs, controlled by the B screw (body angle screw). This adjustment is checked when the chain is on the smallest front sprocket and the largest rear cog.

The majority of road and mountain bike derailleurs require a gap between 5-6 millimeters. Use a hex wrench to gauge this distance, but don't get too hung up on the exact measurement. If the bike is shifting well, the B screw is adequately set. Consult the manufacturer's specifications for any exceptions.

To increase the gap, tighten the B screw. To decrease the gap, loosen the B screw. If you made significant changes to the B screw, double-check the indexing adjustment.

Final Checks and Troubleshooting

Once you've completed the adjustments, it's essential to test ride the bike. The stresses on the drivetrain during actual riding may reveal issues that weren't apparent while adjusting the bike on a repair stand.

If you encounter symptoms like slow shifting or excessive noise during the test ride, follow the same guidelines discussed in the video. You may need to adjust the barrel adjuster or limit screws by another quarter turn.

If something didn't seem quite right during the adjustment process, refer to our video on advanced troubleshooting and rear derailleur adjustment for further guidance.

Proper rear derailleur adjustment takes practice, but with the right techniques and patience, you can achieve optimal shifting performance and enjoy a smoother, more enjoyable ride.

FAQ

Q: What is a rear derailleur?
A: The rear derailleur is the mechanism that shifts the chain at the rear cogs.

Q: What is the purpose of the limit screws?
A: The limit screws prevent the derailleur from moving too far inward (H limit screw) or too far outward (L limit screw), preventing the chain from going into the spokes or frame.

Q: What is indexing?
A: Indexing is the process of lining up the guide pulley with the cogs, so that each incremental shift lines up with each cog.

Q: What is the function of the barrel adjuster?
A: The barrel adjuster allows you to move the shift increments, enabling you to fine-tune the indexing.

Q: How do you set the H limit screw?
A: Tighten the H limit screw until it causes excessive noise or shifting to the next cog, then loosen it in quarter-turn increments until the noise and shifting issues are resolved.

Q: How do you index the rear derailleur?
A: Shift through the gears and adjust the barrel adjuster counterclockwise until excessive noise occurs, then turn it back clockwise in quarter-turn increments until the noise is gone and shifting is smooth.

Q: How do you set the L limit screw?
A: Tighten the L limit screw until it causes symptoms like excessive noise or slow shifting to the largest cog, then loosen it in quarter-turn increments until shifting is smooth.

Q: What is the B screw and how do you adjust it?
A: The B screw controls the gap between the guide pulley and the cogs. It is adjusted by tightening or loosening the screw to achieve the recommended gap of 5-6mm (consult manufacturer specifications).

Q: What should you do if issues persist after adjustment?
A: If symptoms like slow shifting or excessive noise show up during test riding, further fine-tune the barrel adjuster or limit screws in quarter-turn increments. Also, consult advanced troubleshooting guides if problems persist.

Q: Why is it important to properly adjust the rear derailleur?
A: Proper rear derailleur adjustment ensures smooth and precise shifting, optimizing the performance and efficiency of your bike's drivetrain.