Adjusting the Rear Gear Changer

The rear derailleur is akin to the unsung hero of a pro cycling team - it works tirelessly, yet is often overlooked in the scheme of things. Not many of us truly appreciate its importance until it fails to function optimally, resulting in a ride that’s noisy, and less than smooth.

So, the next time you scale a hill with a little less effort, take a moment to acknowledge this marvel of engineering. Here's an in-depth explanation of how rear derailleur adjustment works, along with some tips to keep your bike running like new.

Understanding how the rear derailleur adjustment works

The rear derailleur is what shifts the chain across the sprockets, while providing durable tension to the chain during a gear change. Two jockey pulleys on the rear derailleur facilitate the chain's movement. As you shift to a larger chainring or cog, the shifter cable tugs the rear derailleur forward, prompting the pulleys to push the chain onto the bigger sprockets, while ensuring that the tension remains consistent.

Conversely, when shifting to a smaller ring or cog, the shifter cable releases the rear derailleur, enabling it to move outwards, taking up the chain slack and pulling the chain onto a smaller sprocket. Provided your settings are accurate, a clean shift should occur for every click of your shifter.

Deconstructing the components of a rear derailleur

Kent Pell

The b-knuckle pertains to the upper region of the derailleur. On Shimano and SRAM derailleurs, the b-tension adjuster fine-tunes the height of the guide pulley. Conversely, on Campagnolo derailleurs, this is accomplished via a screw near the p-knuckle. The barrel adjuster regulates cable tension. The guide pulley ensures that the chain stays in line throughout every shift, whereas the idler pulley helps hold chain tension in place, regardless of gear choice.

The mounting bolt connects the derailleur to the bike frame, while the parallelogram linkage enables the chain to move laterally, and up and down the cassette whilst remaining parallel to the sprockets. The high and low limit stops are usually situated near the b-knuckle or occasionally at the front of the parallelogram. The low limit (often marked L) prevents the chain from overrunning the spokes, while the high limit (marked H) stops the chain from dropping off the smallest cog. Meanwhile, the p-knuckle holds both the guide pulley and a spring that keeps the cage taut to hold the chain steady, while the cable bolt pinches the shift cable in place. On most derailleurs, pulling the cable via the shift lever shifts the derailleur up the cassette to a lower gear; except with Shimano’s low-normal derailleurs, which function in the opposite way. The cage facilitates the chain's positioning between the pulleys.

How to adjust and align the rear derailleur

If your chain stays put when you shift gears or skips cogs, it’s possible that your rear derailleur is misaligned. Step off your bike and follow these instructions: Shift your chain into the largest chainring and smallest cog, then loosen the cable clamp bolt (where the cable connects to the derailleur).

Adjusting your derailleur can greatly improve the performance of your bike. To begin, leave the derailleur in the smallest cog and adjust the high limit screw. The high and low adjusters are typically labeled H and L on the derailleur. Adjust the high-gear screw until the jockey pulleys align with the smallest cog. Your chain should move smoothly around the cog and pulleys as you pedal.

To check alignment with the largest cog, rotate the pedal forward and push the rear derailleur until the chain shifts to the largest cog. If the pulleys take the chain beyond the largest cog, screw the low adjuster inward until this stops. Reattach the cable and tighten the clamp.

After adjusting the limits, pull the slack out of the cable and tighten the clamp. Use the barrel adjuster, located where the cable housing enters the rear derailleur, to fine-tune the tension for precise shifts. For optimal performance, position the guide pulley approximately 6-7mm away from the cogs. If your chain skips when you shift to a lower gear, give the barrel adjuster a half-turn counterclockwise. To shift to a higher gear, try a half-turn clockwise.

Once you've completed your adjustments, clean the pivot points with a few drops of bike chain lube and cycle through a few shifts. Wipe off any excess lube and clear any debris from the inner and outer surfaces of both pulleys. These simple steps can greatly enhance your bike's performance and make your ride smoother and more enjoyable.

A Comprehensive Guide on Changing a Rear Derailleur

To start the process of replacing your rear derailleur, the first step is to remove the chain by locating the quick removal link, which most chains use for easy removal. If your chain doesn't have a quick removal link, you can break it with a chain tool or remove the connecting pin and replace it with a new one to rejoin the chain.

Next, loosen the cable-clamp bolt on the rear derailleur and pull out the shifter cable. Be sure to remember where the cable was positioned before removing it to ensure proper placement later.

The next step is to undo the hex bolt that attaches the derailleur hanger from the rear dropout. Gently remove the derailleur from the bike frame and take note of its orientation for reinstallation.

Tools You Need to Replace Your Chain:

• - Topeak Universal Chain Tool: Now 23% off

This chain tool is designed to work with any chain type and comes with a chain hook too. It makes chain replacement easier and quicker.

- Park Tool Chain Checker Tool:

This tool allows you to gauge the wear on your chain by checking its stretch. It helps you determine when it's time to replace the chain.

- Park Tool Bicycle Chain Master Link Pliers: Now 14% Off

This pliers tool is great for working with chains with master links. It allows you to easily open or close the links of your chain, which is useful during repairs and maintenance.

Credit: Topeak and Park Tool for their high-quality chain replacement tools.

Discounted by 19%, the Crankbrothers M19 Multi-Tool comes equipped with a Universal Chain Tool, and is a must-have for all bike maintenance enthusiasts. Ensure that your new derailleur is compatible with your bike’s shifters, keeping in mind that eight- through 11-speed shifters must be matched with the same manufacturer’s equivalent derailleur. Use a hex bolt to attach the new derailleur to the hanger, then reattach the cable and loop the chain through the jockey wheels before reconnecting it. Testing the gear combinations is also essential to ensure smooth performance, and if anything seems off, fine-tune shifting by adjusting the barrel adjuster on the derailleur.

Renowned as a bestselling author, journalist, photographer, and broadcaster, Chris Sidwells is a cycling connoisseur who covers every aspect of cycling and cycles. His work has been featured in publications such as Men’s Fitness, GQ, Cycle Sport, and Cycling Weekly, and he is also the author of prominent cycling literature such as A Race for Madmen: A History of the Tour de France, Tour Climbs: The Complete Guide to Every Mountain Stage on the Tour de France, The Long Race to Glory: How the British Came to Rule the Cycling World, Complete Bike Manual, and The Art of the Cycling Jersey. He currently resides in the United Kingdom.