Condensed answer: A clutch derailleur is not obligatory for a single drivetrain (1x), but it certainly helps with chain retention when using a large cassette and riding off-road.
What is a 1x drivetrain?
1x drivetrains have a single chainring and thus do not require a front derailleur.
1x drivetrains have two main advantages:
- Simplicity (+aesthetics)
- Lower weight
Over the years, 1x drivetrains gained popularity in the MTB sector and eventually entered the road bike segment, albeit to a smaller extent.
1x drivetrains have 2 major issues:
- Problematic chain retention in high gears
- Excessive chain movement on off-road terrain
What is the purpose of clutch derailleurs?
A normal rear derailleur tensions the chain via a single spring. If you grab the lower jockey wheel and push the derailleur forward, you will find some resistance, but you will still be able to move the derailleur’s cage towards the front wheel.
The tension spring found in a regular derailleur has proven to be insufficient to prevent movement of the derailleur’s cage when riding on extreme terrain. The derailleur tends to move forward when riding over bumps. That forward motion creates additional slack in the chain. As a result, the chain moves excessively up and down and slaps the chainstay. (Hence the need for chainstay guards).
Sometimes, the slack could result in a fallen chain – an unpleasant and potentially dangerous outcome.
By adding a clutch to the derailleur, it becomes much harder for the cage to move forward. The clutch is essentially another wave of defense besides the original spring preventing unwanted movement of the rear derailleur. If you push the cage of the derailleur harder, it will still move a bit but will require a lot more force.
The clutch ensures that the chain will remain sufficiently tense even when going over bumps. As a result, the user enjoys better chain retention and greatly reduces the unwanted vertical movement of the chain.
FAQ: What are the downsides of a clutch derailleur?
Besides the extra price, the only downside of clutch derailleurs is that the clutch makes shifting less fluid and snappy. That said, the effect is not noticeable in practice.
Clutch derailleurs have an on/off switch to engage or disengage the clutch. If the user considers the clutch non-needed for the particular drivetrain, it can be disengaged so that the shifting motion can be smoother and faster.
Are clutch derailleurs needed for a 1x drivetrain?
The technical answer is no, but they can certainly help significantly.
1x drivetrains often have issues with chain retention because of the large rear cassette. Since there is a single chainring at the front, 1x drivetrains require a cassette with both very high and low gears.
In other words, the difference between the smallest cog (high gear) and the largest one (lowest gear) on such cassettes is massive. (e.g., 11 teeth vs. 42 teeth).
Smaller cogs require a shorter chain whereas large cogs need a longer one. When you combine both, you get problems with chain retention when riding in the smallest cogs due to the extra chain length needed for riding in the largest cog.
A clutch derailleur minimizes those issues by keeping the chain maximally tensioned at all times.
That said, a clutch derailleur is not absolutely mandatory for having a successful 1x drivetrain setup.
Below are some tips and conditions that influence chain retention too:
- Cassette size
If the difference between the smallest and the largest cog of the cassette isn’t massive, then the chain retention offered by a basic derailleur could be sufficient, especially if the rider doesn’t intend to cover off-road sections.
- Narrow-wide Chainrings
Narrow-wide chainrings have teeth of altering width helping chain retention. For that reason, you will find a narrow-wide chainring on almost every 1x setup.
- Third-party Chain Tensioner/Guide
Another way to reduce the chain slap and improve chain retention is the use of third-party chain tensioners. Those aren’t as popular anymore, mainly due to the presence of clutch derailleurs and narrow-wide chainrings, but they worked fine before and still do.
Some of those models mimic a front derailleur while others are installed on the drive side chainstay.
- Front Derailleur
The cheapest way to improve chain retention on a 1x drivetrain is to simply keep the original front derailleur as a guide. The limit screws will have to be re-adjusted so that the derailleur’s cage is positioned at the right place to keep the chain on the chainring.
Summary: What You Need To Know
- Clutch derailleurs help with chain retention by adding a strong spring mechanism to prevent the lower jockey wheel from moving forward when covering off-road terrain.
- 1x drivetrains require cassettes with a very large rear cog to preserve the low gearing of the bike.
- 1x drivetrains create massive chain slack when riding in higher gears due to the discrepancy between the smallest and the largest cog. The outcomes are chain slaps to the frame and possibly a fallen chain that can cause an accident.
- A clutch derailleur reduces a lot of the chain slack and greatly improves chain retention without requiring a third-party chain guide. Consequently, many people prefer to pay the extra price for a clutch derailleur.
- A clutch derailleur is not mandatory for creating a working 1x drivetrain. If the difference between the smallest and the largest cog isn’t enormous, and the user relies on a narrow-wide chainring, then the setup could be operational without a clutch.
- Whether a clutch will be needed depends on the terrain too. Extreme riding will greatly benefit from a clutch derailleur.
- Additional chain retention can be obtained by using chain tensioners near the chainring or the chainstay.
