Why does your road-bike front derailleur keep rubbing?

Front-derailleur rub is not always cured by turning a limit screw. First identify the exact front and rear gear combination, try the shifter’s trim position if it has one, and watch which side of the derailleur cage the chain touches. Then inspect alignment, cable condition, chainring runout, and crank play before adjusting anything.

The short answer: occasional rub in an extreme chain angle may be avoided by choosing the neighbouring gear or using the model’s trim function. Rub through useful middle gears is a setup or component clue. Do not keep turning both limit screws: follow the exact derailleur manual in its stated order, or give a mechanic a precise symptom map.

Why repeated adjustment sometimes changes nothing

A well-discussed r/bikewrench case described front-derailleur rub returning after several shop adjustments. The discussion eventually widened from indexing to a chainring that might not run straight. That is the valuable signal: the cage is only one possible moving reference.

Modern road front derailleurs differ substantially. Some use a trim click, some have model-specific support bolts, some route cables differently, and electronic systems have their own adjustment procedures. Shimano’s general dealer manual shows separate road procedures and trim positions; it is not permission to apply one clearance number to every derailleur.

Make a rub map before touching a screw

Support the bike securely, keep fingers away from the moving chain, and turn the cranks by hand. Shift normally—never force a stationary drivetrain.

Record the result in all useful combinations:

1. small chainring with the largest, middle, and smallest rear sprockets;
2. big chainring with the largest, middle, and smallest rear sprockets;
3. before and after any deliberate half-click or trim command;
4. under hand rotation and, later, under light riding load.

Note whether the chain touches the inner cage plate, outer plate, only one point per crank revolution, or continuously. A repeatable map is far more useful than “it rubs in some gears.”

Avoid prolonged big-ring/big-sprocket and small-ring/small-sprocket use. Cross-chaining increases chain angle, but it should not be used to dismiss rub across the middle of the cassette.

Use the sound pattern to narrow the cause

Pattern	Likely area to inspect
Rub disappears with a trim click	Normal trim use or fine adjustment
Rub only in one extreme chain angle	Gear choice, trim, or model-specific setup
Rub across several middle sprockets	Cage alignment, height, rotation, cable tension, or compatibility
Rub once per crank revolution	Bent or mis-seated chainring, crank/spider issue, or lateral play
Clearance changes when pedalling hard	Crank/bottom-bracket play, loose parts, frame flex, or setup at the limit
Chain overshifts or drops	Limit, alignment, support, cable, or compatibility fault
Problem began after wheel or crank work	Reassembly, spacer, chainline, or component seating issue

Do not diagnose a bent chainring by trying to straighten it while installed. A mechanic can measure lateral runout and check the crank, spider, bolts, axle, and bearings as a system.

Identify every relevant part

Write down:

• shifter model;
• front-derailleur model and mounting type;
• crank and chainring sizes;
• number of rear speeds and cassette range;
• chain model and direction, if directional;
• frame make, model, and any derailleur adapter;
• whether the system is cable-operated or electronic.

“Shimano 105” is not specific enough because generations and combinations differ. Search the manufacturer’s technical library using the printed model code. Confirm that the parts are listed as compatible before following an adjustment procedure.

Inspect without adjusting

With the bike clean enough to see the parts:

1. Check that the derailleur mount, adapter, and cage are secure.
2. Sight the cage relative to the large chainring as the manual instructs.
3. Turn the crank slowly and watch whether the chainring moves side to side.
4. Hold the crank arms and check for lateral play without forcing them.
5. Inspect chainring teeth, bolts, crank interfaces, cable, housing, and electronic wiring.
6. Look for a polished rub mark to identify the contact plate and height.

A dirty chain can sound rough, but lubricant does not fix metal-on-metal cage contact. Keep lubricants away from brakes and wipe excess from the chain.

Understand the four setup variables

Cage position

Height and rotation determine how the cage follows the chainrings. Some derailleurs also require a support bolt or backing plate against the frame. Guessing can damage paint or a carbon frame.

Limits

Limit screws constrain inward and outward travel. They are safety boundaries against overshifting, not general noise knobs. Tightening a limit to hide rub can prevent a shift; opening one can let the chain drop.

Cable tension or electronic adjustment

Cable tension affects the operating positions on many mechanical systems, but routing and sequence matter. Electronic systems use model-specific adjustment modes. Do not pull a cable harder or enter a menu from a different generation’s video.

Trim

Trim moves the cage slightly without completing a front shift. The lever action and available positions vary. Learn it using the road-bike gears guide and the shifter manual.

When to stop the home adjustment

Use a qualified mechanic when:

• the chainring is visibly damaged or runs laterally;
• there is crank or bottom-bracket play;
• the derailleur or mount is loose, bent, or cracked;
• the chain has already dropped and marked the frame;
• compatibility cannot be confirmed;
• a carbon-frame support surface, bonded mount, or proprietary adapter is involved;
• the rub returns immediately after a correct full procedure.

Ask the mechanic to record the cause, not only “adjust front mech.” That makes recurrence easier to diagnose.

Verify the repair in stages

After a model-correct adjustment, turn the cranks by hand and shift through the permitted combinations. Confirm the chain cannot overshift either chainring. Then test at walking pace in a traffic-free place, using light pedal pressure. Only increase load after every shift is predictable.

Stop if the chain hesitates, jams, falls, or the cage is struck. Shifting under maximum uphill load is a poor test and a good way to turn a small adjustment issue into a damaged chain or frame.

Your next step

Make the six-combination rub map and find the printed derailleur model code. If the noise occurs once per crank revolution or the crank has side play, do not touch the limit screws—book a mechanical inspection. Otherwise, follow the exact manufacturer’s sequence from the beginning rather than continuing the last person’s adjustment.

Sources and further reading

• Shimano: General Operations dealer manual, including road front derailleurs
• Shimano technical documents search
• r/bikewrench reader context: persistent rub after repeated adjustment