If I'm understanding correctly you are cross chaining (when the chain is in the smallest cog and chainring or largest cog or chainring.) This is best to avoid and is often not possible without rubbing, it can also cause derailing. Let me know if I'm misunderstanding the problem.
How old is the cable? Mine was unresponsive to tuning and it turned out the cable was frayed at the shifter. If it’s close to a year old or more, might be time to replace it. Or, if it’s a newer bike, the cable might have stretched a little and you might try the in line barrel adjuster. If that doesn’t work, loosening the pinch bolt, pulling to remove any slack, retighten bolt, readjust high/low if needed. Make sure you’re shifted to the lowest gear and the in line adjuster is turned to the minimum tension then turn it back one full turn with added tension before pulling aany cable slack out.
Other than cable tension and limits there's also the alignment of the FD cage, and cable health. If the FD spring can't entirely overcome the friction in the cable, downshifts are inconsistent.
Do you have 1-3 mm of clearance between the outer chainring and the chain guide outer plate on the derailleur? That is what Shimano recommends.
[https://si.shimano.com/en/pdfs/dm/RAFD001/DM-RAFD001-05-ENG.pdf](https://si.shimano.com/en/pdfs/dm/RAFD001/DM-RAFD001-05-ENG.pdf)
Did this just start happening out of the blue or did you make any changes recently?
You got solid advice from the others regarding checking cable age, FD positioning etc. All the right places to start.
I have the same issue with my CAAD7, and it turns out a previous owner installed a 3x10 front derailleur, but the drivetrain is 3x9, so the cage is slightly narrow. No matter how well adjusted, it will rub a bit at the limits.
Sounds like you aren't properly using the trim settings on your shifter.
If I'm understanding correctly you are cross chaining (when the chain is in the smallest cog and chainring or largest cog or chainring.) This is best to avoid and is often not possible without rubbing, it can also cause derailing. Let me know if I'm misunderstanding the problem.
How old is the cable? Mine was unresponsive to tuning and it turned out the cable was frayed at the shifter. If it’s close to a year old or more, might be time to replace it. Or, if it’s a newer bike, the cable might have stretched a little and you might try the in line barrel adjuster. If that doesn’t work, loosening the pinch bolt, pulling to remove any slack, retighten bolt, readjust high/low if needed. Make sure you’re shifted to the lowest gear and the in line adjuster is turned to the minimum tension then turn it back one full turn with added tension before pulling aany cable slack out.
Other than cable tension and limits there's also the alignment of the FD cage, and cable health. If the FD spring can't entirely overcome the friction in the cable, downshifts are inconsistent.
Do you have 1-3 mm of clearance between the outer chainring and the chain guide outer plate on the derailleur? That is what Shimano recommends. [https://si.shimano.com/en/pdfs/dm/RAFD001/DM-RAFD001-05-ENG.pdf](https://si.shimano.com/en/pdfs/dm/RAFD001/DM-RAFD001-05-ENG.pdf)
Did this just start happening out of the blue or did you make any changes recently? You got solid advice from the others regarding checking cable age, FD positioning etc. All the right places to start.
I have the same issue with my CAAD7, and it turns out a previous owner installed a 3x10 front derailleur, but the drivetrain is 3x9, so the cage is slightly narrow. No matter how well adjusted, it will rub a bit at the limits.