Having an issue with my winter/commuter bike at the moment with chain rub. I have adjusted it countless times and on the workstand its running butter smooth with no problems.
When riding I don’t use the last 2 cogs on the cassette when in the large chainring to avoid cross chaining. But in the 3rd cog down from the largest on the cassette when I’m out the saddle it rubs but sat down its not as bad? Could this be frame Flex? It’s an alloy frame with 9 speed Sora groupset. I have set up the gears to have the low limit set to 2mm off the derailleur in the little/big combo and then 2mm off the derailleur on the big /little.
More likely some wheel / hub ‘flex’ with a misaligned mech. Is the outer cage of your front mech parallel / inline with your large chainring? If it’s nosed in even a small amount it can cause the inner plate to rub earlier than expected when changing up the block.
Well sometimes getting the front derailleur tuned can be a fiddly process. I like to keep it so that if I’m on the big ring on the front and the 2nd-to-largest cog on the back I get a just a little bit of front derailleur chain rub. That gives me a little audio cue that I’m wasting watts…but if it’s a critical race situation I can still give the shifter a trim click and eliminate the chain rub.
