As you pedal down the road, the last thing you want is the jarring sound of your bike chain grinding against the front derailleur.
It’s super annoying and it can also reduce performance and damage your drivetrain.
If you’re experiencing this issue, it’s important to understand why it happens. From misalignment to incorrect chain tension, there are a few reasons why your chain rubs on front derailleur.
In this post, we’ll explore the common causes and how to fix each one of them.
Is It Normal for the Chain to Rub on Front Derailleur?
No, it is NOT normal for the chain to rub on the front derailleur. Your derailleurs should give smooth and precise shifting without any chain rubbing.
Also Read: Front Derailleur Not Shifting
Chain rubbing on the front derailleur is a problem and you should address this issue to ensure optimal performance and to prevent excessive wear on the drivetrain components.
Why Is My Chain Rubbing On Front Derailleur?
Here are some of the possible reasons why your chain rubs on front derailleur:
Derailleur Misalignment
When the front derailleur is misaligned with the chainrings, it can cause the chain to rub against the derailleur cage.
If the derailleur is not parallel to the chainrings, the chain may not smoothly transition from one chainring to another, leading to rubbing and potential noise.
The misalignment can happen due to various factors such as accidental knocks, improper installation, or general wear and tear.
Limit Screw Adjustment
The limit screws on the front derailleur define the endpoints of its movement range. If the low limit screw, specifically, is not properly adjusted, the derailleur may not position itself correctly in the lowest gear.
This can cause the chain to rub against the inner cage of the derailleur.
When the chain rubs in the lowest gear, it typically means that the derailleur is positioned too far towards the frame, resulting in insufficient clearance for the chain.
As a result, the chain may come into contact with the inner cage, causing friction and noise.
Cable Tension
Improper cable tension also contributes to chain rubbing. If the cable tension is too loose, it may not provide enough force to move the derailleur smoothly, causing the chain to rub against the derailleur cage.
When the chain rubs against the derailleur cage due to inadequate cable tension, it can lead to inconsistent and sluggish shifting performance.
Also Read: Bike Chain Slipping When Pedaling Hard
It mostly happens in the lowest gear due to the increased slack in the cable.
Additionally, the chain may have difficulty moving smoothly from one chainring to another.
Chainline
Chainline is the alignment of the front chainrings with the rear cassette. An improper chainline can cause the chain to rub against the front derailleur.
If the chainline is off, meaning the chainrings are not properly aligned with the cassette, the chain may not track smoothly and may rub against the derailleur cage, especially in the lowest gear.
A misaligned chainline can result from factors such as incorrect chainring spacing, improper installation of the chainrings, or incorrect bottom bracket spindle length.
Bent Derailleur Hanger
The derailleur hanger is a small piece of the frame where the derailleur is mounted.
If it becomes bent or misaligned due to accidental impacts or mishandling, the derailleur’s position can be affected.
A bent derailleur hanger can prevent the front derailleur from aligning properly with the chainrings, causing the chain to rub against the derailleur cage.
How To Stop Chain Rubbing On Front Derailleur
Now that you know the causes, let’s see how to fix each of these:
Also Read: Shimano Derailleurs With SRAM Cassettes
Misalignments
To fix misalignment between the front derailleur and the chainrings:
- Loosen the mounting bolt of the front derailleur, allowing it to move freely.
- Align the derailleur cage parallel to the chainrings, ensuring a small gap (around 1-3mm) between the cage and the chain in the lowest gear.
- Hold the derailleur in the aligned position and tighten the mounting bolt securely.
- Check the alignment again to ensure it remains parallel to the chainrings.
- Test the shifting to ensure smooth operation and eliminate any chain rubbing.
Adjusting Limit Screws
To adjust the limit screws on the front derailleur:
- Locate the low limit screw, usually labeled “L” on the derailleur.
- Turn the low limit screw in small increments counterclockwise to increase clearance between the inner cage and the chain in the lowest gear.
- Shift through the gears to verify that the chain moves smoothly without rubbing against the derailleur cage.
- Make fine adjustments as needed, ensuring the chain stays on the chainrings while eliminating any rubbing in the lowest gear.
Adjusting Cable Tension
To adjust the cable tension on the front derailleur:
- Shift the chain to the smallest chainring and the smallest rear cog (highest gear).
- Locate the barrel adjuster on the front derailleur or at the cable entry point.
- Turn the barrel adjuster counterclockwise to tighten the cable tension.
- Shift through the gears, monitoring for smooth and precise shifting. If the chain still rubs, make additional adjustments to fine-tune the tension until the rubbing is eliminated.
Bent Derailleur Hanger
If the hanger is indeed bent, it is best to have it repaired or replaced by a professional bike mechanic.
They have specialized tools, such as a derailleur hanger alignment gauge, to accurately realign the hanger.
The mechanic will carefully align the hanger to ensure proper positioning of the front derailleur and you should be good to go.
FAQs
Why Is My Chain Rubbing On Front Derailleur In High Gear?
Your gear cable requires more tension to extend the derailleur further outward. Twist the barrel adjuster in a counter-clockwise direction to fix this. You should be able to find a barrel adjuster either on the down tube or an in-line one.
Why Is My Chain Rubbing On Front Derailleur In Lowest Gear?
The most common reason for chain rub on the front derailleur in the lowest gear is that the limit screw is not adjusted properly. Loosen the limit screw by turning it counterclockwise.
