Oftentimes, working on your bike can be just as satisfying as riding it. One of the most essential jobs to know how to do is how to adjust or install a rear derailleur.
If you’re building a bike or yours has seen better days and needs replacing, knowing how to install a rear derailleur could save you a trip to the bike shop!
On the surface, the rear derailleur looks easy to install, since it is only one bolt. However, the difficulty comes in setting it up correctly.
Once you know how to install a rear derailleur, it’s not a particularly challenging job, and in this article and video, we’ll show you how to install a rear derailleur, and how to make sure that it’s set up correctly for smooth and efficient shifting on your bike.
Here’s what we will be covering:
- What Is A Rear Derailleur?
- Identifying That You Need A New Derailleur
- What Tools Will You Need To Install A Rear Derailleur?
- How To Adjust or Install A Rear Derailleur In 10 Steps
- Robbie’s Video Maintenance Guide: Installing A Rear Derailleur
Got your tools at the ready?
Let’s get started!
What Is A Rear Derailleur?
A rear derailleur is one of the most vital parts of the bike. It provides the ability to move the chain up and down the cassette, thereby changing the gear. The rear derailleur is responsible for the gears that allow you to climb hills easily and also descend quickly.
A rear derailleur is typically controlled through the action of the shifters via a cable, although some modern versions work electronically. Relying on precise measurements, if they are 1 mm out on adjustments, you will certainly know about it; your gears won’t work properly.
They come in all shapes and sizes, and you will see some older models with as few as 7 speeds and other more recent releases with up to 12 speeds.
- To find out more about the function of a rear derailleur, check out our guide The Bike Derailleur Explained: Everything You Need To Know!
Identifying That You Need A New Derailleur
A derailleur is part of a bike that typically lasts a very long time. Many cyclists make the mistake of changing the derailleur when it’s not actually broken.
Before discussing replacing a derailleur, here are some other common issues that may be the cause of your shifting issues.
#1. Broken Shifters
It’s not uncommon for people to think their derailleurs are broken when it’s actually their shifters. We recommend testing the shifting without a cable attached to see if they are still in good working order. You can do this by listening for the right clicks.
#2. Worn Cable Inner And Outer
Another common issue is an overly stiff cable. This can result in an unresponsive derailleur that feels broken. We recommend changing them out before, as it’s a much cheaper fix than a new derailleur.
#3. Bent Mech Hanger
A mech hanger is the part of the bike which holds the derailleur. It’s designed to bend if too much pressure is put on the derailleur as a safety mechanism to protect the rear derailleur in case of an accident. It’s a good idea to check if yours is bent first.
#4. Worn Out Chain
A worn-out chain can also make your bike feel like it has a broken derailleur. If the chain is slipping and skipping, you likely have a worn-out chain rather than a broken derailleur.
- Discovered that your derailleur is working fine and it just needs adjusting? Check out our article How To Adjust Derailleurs On A Bike In 4 Steps [With Pictures]!
What Tools Will You Need To Install A Rear Derailleur?
To complete the task of installing a rear derailleur, you will need a few light tools. We recommend having:
- An Allen Key Set
- Cable Cutters
- A Small Phillips Screwdriver
- A Bike Cable End
- A Bike Stand
- Cable Inner And Outer (Optional)
How To Install A Rear Derailleur In 10 Steps
Here’s our guide on how to install a rear derailleur. We recommend allowing an hour to do this job if it is your first time.
Step #1. Preparation And Checks
The first part of the process is to get prepared.
You will need to find a safe place to work where you have lots of space. Get your bike into the stand with the drive side facing you for easy access to the rear derailleur.
Step #2. Install Rear Derailleur On The Hanger And Install The Chain
The next step is to get your new derailleur and screw it onto the frame.
You will need to use the Allen key set and ensure it goes on correctly with the B screw adjuster point sitting on the hanger properly. The torque should be 8-10 nm according to BikeRide.
Then you are going to need to install the chain. Ensure that you insert the chain through the correct path through the derailleur and use a chain that is in good condition and has the correct length.
- Not sure how to install a chain? Take a look at our guide How To Remove And Replace A Bike Chain In 6 Steps [With Pictures]
Step #3. Install Inner And Outer Cables
Although it may not be completely necessary, we highly recommend if you are installing a new derailleur, change your inners and outer cables. While everything is apart, it makes it much easier, and you get the best experience using new parts alongside each other.
Step #4. Set the High Limit Screw
Before tightening the cable onto the derailleur, it’s good to have your high-limit screw set up.
This is what stops the chain from falling off the bottom of the cassette. It is adjusted using the screw indicated with the small “H” on it at the rear of the cassette.
The key to this is to screw it in until it jumps up from the smallest cog to the next one. Then slowly unscrew it until it drops down into the bottom cog and runs smoothly. This limits it to the last cog on the system and ensures that it won’t go over the edge.
Step #5. Install The Cable On The Derailleur
Now you need to install the cable into the derailleur.
First, ensure that the shifter is in its lowest position to ensure the cable run is as long as possible. Pull the cable tight with your hands and hit the shifter into the smallest sprocket. You will feel it release.
Next, screw in the barrel adjuster on the derailleur as much as possible without forcing it. Finally, put the cable in the pinch bolt and tighten it up, nipping it nice and tight.
It’s a good idea to not cut the excess cable until after indexing the gears, just in case you need to re-adjust the location of the pinch.
Step #6. Index The Gears
Now for the fun part: indexing the gears.
You’ll likely be surprised at how easy it is once you know what you’re doing. Click the shifter up a gear while rotating the pedals, and more than likely, nothing will happen.
Then you need to unscrew the barrel adjuster half turn at a time until it jumps up upon rotation of the pedals. Once it has jumped up, shift back down to the bottom gear. Repeat this process on any cogs that need it until you get to the top of the cassette.
You will eventually get to the final gear. The gears should shift up and down the entire cassette efficiently without getting stuck or being noisy.
It might take some time to get right, so don’t be scared to screw the adjuster back in and start again. There’s only a single turn of the adjuster between perfect and messy gearing.
Step #7. Adjust The Low-Limit Screw
Next, you’ll need to adjust the low-limit screw.
You will find this screw next to the high-limit screw but marked with an “L” instead. There are a few different ways of doing this, but generally, the simplest way is the following:
Shift into your lowest gear on the cassette (the biggest sprocket). Screw in the low-limit screw until it jumps down into the next sprocket. Then you will want to slowly unscrew it until it jumps back and works smoothly in the lowest gear without making skipping noises.
Step #8. Cut The Cable And Put The End On
Now you’ve indexed the gears correctly, it’s time to cut the cable (if you put a new one in).
We recommend leaving around an inch after the derailleurs pinch bolt in case you want to make any adjustments in the future. Use the cable cutter to cut it and then put an end cap on.
Step #9. B-Limit Screw
The next job is to adjust the B-limit screw.
This is a small screw on its own and adjusts the (radial) distance between the derailleur and the cassette. Go into the smallest chainring on the front and the largest sprocket on the rear.
You might find the derailleur sits directly on the cassette with the chain running in between. If so, screw the B-limit screw in, and it will create a gap. Ideally, you want around 5-6 mm between the two.
Step #10. Test And Be Preprepared For Adjustments
Finally, it’s a good idea to now give it a real road test.
It is important to mention that if you put a new cable in, you will probably find it will come out of adjustment within 200 miles. This is common, and it’s called cable stretch. It’s just the cable settling in and stretching to its maximum capacity.
You will only need to turn the barrel adjuster out a turn or two, which should fix the issue. If you use high-end cables, they come pre-stretched, so you won’t always need to do this.
Robbie’s Video Maintenance Guide: Installing A Rear Derailleur
Check out the BikeTips YouTube Channel here for walk-through bike maintenance guides and more!
Now You Know How To Install a Rear Derailleur…
When it comes to installing a rear derailleur, it can be challenging, and it’s more about adjusting it to work correctly than it is about getting it on the bike.
However, it’s well worth taking the time to learn how to do it for yourself – especially as so many of the steps in the process will teach you how to make other shifting adjustments in future.