A bicycle can successfully operate in front derailleur-only mode with a few modifications. However, the practical use of this setup is questionable. Hence the lack of popularity.
The Problems With Front Derailleur Only Bikes
- Chain Tension
Larger chainrings require a longer chain whereas smaller ones need a shorter one for optimal tension.
Consequently, one needs a chain tensioner to eat up the chain slack when switching from a larger chainring to a smaller one.
If the chain tension isn’t optimal, the shifting experience will be very poor, and the chain may fall off the chainring.
There are two ways to tension the chain – by keeping the original derailleur or replacing it with a dedicated chain tensioner. The first method is cheaper if you already have a derailleur while the second keeps the drivetrain appearance cleaner. Functionally, they’re identical.
The need for a chain tensioning device is one of the main reasons why people stay away from FD-only drivetrains.
If you’re going to have a rear derailleur or a tensioner that weighs about as much at the back, you might just as well install a cassette and keep the gearing of the bike.
Another very logical option is to switch to a 1x drivetrain and eliminate the front derailleur instead of the rear one. This approach will give a wider gear range as well as smoother gear transitions making it possible to maintain a better pedaling cadence.
The term cadence refers to the number of crank rotations per minute (RPM). Many consider high values such as 90RPM optimal for efficiency and high average speed.
- Limited Gearing
A front derailleur-only bike would have 2 or 3 gears depending on the number of chainrings. In order for the gearing to make any sense, the discrepancy between the chainrings has to be large.
For example, it’s not logical to have a 2×1 setup and install a 44T large chainring and a 42T smaller one.
To get the widest range, use a 3×1 setup with big jumps between the chainrings. E.g., 44/32/22.
Of course, this approach has a massive downside too – it’s impossible to maintain a smooth cadence at all times because you will often be in the wrong gear.
- Poor shifting fluidity
The main benefit of having a large number of gears is the ability to quickly shift between them.
A front derailleur-only bike does not offer that feature and very often you will have to plan your shifts ahead of time (e.g., shifting to the lowest gear before climbing a big hill). Some riders would find the need for planning annoying.
Another issue would be the shifting itself. Switching from an 11T to a 15T cog at the back is easier for the mech than moving from a 44T to a 22T chainring.
In the first case, the chances of a failed shift are lower. In the second scenario, the rider has to be a lot more attentive when making a shift. And if the front derailleur isn’t properly adjusted, the chain may fall.
- Extra Tinkering Is Required
To properly transform a standard bicycle with a rear derailleur into a front derailleur-only machine, one needs to perform the following procedures:
1/ Replace the cassette with a single-speed cog plus spacers. The spacers are needed to make up for the missing cassette cogs. Ideally, the single-speed cog will be in the middle of the driver’s body so that the chain line is perfect when riding in the middle chainring which will be the most frequently used one.
2/ Install a chain tensioner or re-install the rear derailleur.
3/ Adjust the chain length. (Since you won’t be using large rear cogs, the chain will have to be shortened.)
Note: It may also be necessary to replace the chainrings if you want to increase or decrease the gearing.
The Advantages of Running Only a Front Derailleur
- Simplicity
The main incentive to rely on a similar setup is to make the drivetrain simpler and cleaner. To a very large extent, this outcome is achieved if one can look past the need for a chain tensioner.
- Robustness
Front derailleurs are cheaper and simpler. Once properly adjusted, they can operate flawlessly for a long time. Also, they’re protected by the chainring, the frame, and even the rider’s feet.
During a fall, a rear derailleur can easily be damaged. Hence the existence of derailleur hangers. The hangers are made of brittle aluminum meant to break and prevent damage to the frame.
Meanwhile, a front derailleur rarely has to complain after a fall.
- Uniqueness
2×1 and 3×1 setups are very rare. You’re unlikely to see one in real life, although it’s technically not impossible. If you want to have a unique drivetrain, this method will provide it.
