Condensed answer: A clutch derailleur could be helpful when running a 1x drivetrain. In all other cases, it wouldn’t play an important role when it comes to road bikes and is therefore not required for the normal function of the drivetrain.
What is a clutch derailleur?
Standard rear derailleurs have three main functions:
- Move the chain from one cog to the next
- Help chain retention
- Maintain optimal chain tension
In the case of regular derailleurs, the chain tension is maintained via a single spring controlling the lower arm of the derailleur. If you grab a rear derailleur and move its cage toward the front wheel, you will create slack in the chain.
The spring of non-clutch derailleurs could be insufficient when the rider is running a single chairing at the front (a 1x drivetrain).
The reason for this phenomenon is the length of the chain required by wide range 1x drivetrains.
A 1x drivetrain has a single chainring. To keep access to low gears, 1x drivetrains rely on cassettes with very large cogs (e.g., 42 teeth). The discrepancy between the smallest cog (highest gear) and the largest cog (lowest gear) creates chain issues.
The smallest cog requires a short chain whereas the largest one needs a lot of chain length. The greater the difference between the smallest and the largest cog, the harder it becomes for the derailleur to maintain the needed chain tension.
This is where clutch derailleurs come in. They have a secondary spring that makes it a lot harder for the tension arm of the derailleur to move forward and decrease the chain tension.
The extra stability eliminates chain falls and slaps to the drive side chainstay when passing over bumps. For that reason, clutch derailleurs are found on most MTBs running a 1x drivetrain. The world of road cycling is different.
Does a road bike really need a clutch derailleur?
A road bike that uses more than a single chainring, doesn’t benefit as much from a clutch derailleur because it can have low gearing without relying on a massive cassette.
Consequently, the chain tension will be sufficient even with a standard derailleur. Let’s not forget that 2x and 3x road bikes have existed long before the invention of the clutch derailleur.
The front derailleur needed for the movement of the chain from one chainring to the other keeps the chain on track and stops it from falling. Of course, the front derailleur has to be adjusted properly to do that job.
It’s important to mention that road bikes are not designed for off-road and spend most of their time on paved roads. This reduces the need for a clutch derailleur even further.
Of course, there are cobbles, limestone sections, and gravel transitions that will increase the likelihood of chain slabs to the frame. For that reason, many people with standard derailleurs install chainstay protectors even on road bikes. (Mine is a piece of plastic folder attached to the chainstay with zip-tie stitching).
Ultimately, the only situation that could legitimately require the use of a clutch derailleur would be a 1x drivetrain.
But even in that case, it’s not always mandatory to use a clutch derailleur for the following reasons:
- Narrow-wide chainrings
Narrow-wide chainrings have teeth of altering thickness. Those dimensions help with chain retention.
- Chain Guides
By placing a chain guide on the seat tube, one can greatly improve chain retention when running a 1x drivetrain. If a chain guide isn’t available, it’s also possible to use the original front derailleur after readjusting its limit screws.
What Are The Downsides of Running a Clutch Derailleur On a Road Bike?
Clutch derailleurs have two downsides:
- Higher cost
- More difficult shifting
The extra thick spring and the mechanism surrounding it make clutch derailleurs somewhat stiff. As a result, it takes more effort to shift.
The difference between a regular and a clutch derailleur in terms of shifting isn’t massive, but it’s there.
Clutch derailleurs have an on/off switch disengaging the clutch precisely because some users may want a smoother shifting experience.
Summary: What You Need To Know
- Clutch derailleurs reduce chain slaps to the frame and improve chain retention via an additional spring keeping the tension arm of the derailleur rigid.
- Clutch derailleurs shine the most when using a single chainring.
- 1x drivetrains require larger cassettes resulting in a big size discrepancy between the smallest and the largest cog. The largest cog requires a longer chain and when the chain is on the smallest cog, it’s too slack. Without a clutch derailleur, the chain moves up and down too much and may even fall off. That outcome is more common when riding off-road.
- The vast majority of road bikes do not need a clutch derailleur because they use 2x (mostly) and 3x (rare) drivetrains. In those situations, the clutch isn’t all that helpful because the cassette is smaller and the front derailleur keeps the chain on the rings.
- Additionally, road bikes are designed for paved sections and do not generate enough vibration for massive vertical movement of the chain to occur.
- Ultimately, a clutch derailleur would be beneficial but not absolutely mandatory only when running a 1x drivetrain and/or riding a gravel bike.
- Clutch derailleurs are more expensive and make shifting slightly harder when the clutch is engaged.
- The clutch can be disengaged when it’s not needed.
