Chain rub under load

[Lozw86]

Hi there. I have Canondale Synapse with Tiagra drivetrain. Upon receipt of the bike the front and rear derailleur setup was poor. I have since indexed the rear mech and increased the tension of the front derailleur cable to move it to the right slightly, to stop chain rub. It runs pretty well now except for:

- when on the large chainring, if I go onto the two smallest cogs of the cassette, the chain rubs (I think) on the right hand side of the front derailleur cage

- when on the large chainring, if I go onto the three smallest cogs of the cassette and apply full power, sat down or stood up, the chain rubs (I think) on the right hand side of the front derailleur cage

Do you think I just need to further increase the tension of the front derailleur cable to move the derailleur further to the right? Or, given the rubbing under power, is the chainring flexing? As I have got fitter and stronger, I’m wanting to be in these high gears more and the rubbing is very annoying and no doubt wearing the drivetrain

Any input or suggestions appreciated. Thanks

[Norgles]

Sounds more like poor front derailleur alignment rather than tension or the high and low limits. Have you checked the alignment looking at the derailleur from above to ensure the chain does not rub when it is at the extremes of the rear cassette and in the big ring?

That is where I would start.

[Centurion07]

I have similar; little bit of rub when on cogs 7/8/9 but goes away on 10/11 and 1-6. How does that work?!