Originally Posted by
grumpus
He says the front mech rubs under load, a common cause of rubbing things is flex, and a cause of excessive flex is frame failure. Might as well eliminate the major problems before getting down to fine tuning. It could just be that there's a bit of play in the bottom bracket, or the front high limit needs backing off a bit, or other things. But no amount of adjustment in the stand is going to achieve anything if the problem isn't adjustment.
OP said "
Hello, I’m hoping to find some help with a bike front derailleur function issue. I’m working on my brother’s bike (Trek 1220 Road Bike). Just doing some general maintenance. Bike has a triple front derailleur. I completed making sure the rear derailleur was tuned well and moved onto the front. I noticed the front derailleur cable was slightly frayed at the end and decided to replace it."
You're right that it's best to eliminate major problems before getting down to fine tuning. But if the only reason for replacing the cable was that it was frayed, that likely means that the shifting was fine beforehand.
My guess (assuming the limit screw hasn't been moved) is that the inner wire is now insufficiently taut to keep the chain on the big chainring. It's easy to get the tension wrong when installing a new shifter wire, especially with a road triple crankset.