Originally Posted by
urbanknight
Looks like I responded while you were adding this. You're saying that both adjustments are only a factor while shifting, but I was wondering if the bottom bracket shell flexing (i.e. during a sprint or climbing out of the saddle) could play a part. Perhaps not.
Come to think of it, many many years ago I had a miserable Raleigh Super Course that would give me chain rub when I stood hard on the cranks. I never knew whether it was the bottom bracket spindle, the crank spider, or the chain stays flexing enough to deflect the chain. It seemed to go away when I put a Stronglight 93 crank on it, but that bike was pretty whippy. I used to also hear of chain stay flex on some steel bikes that would cause the rear derailleur to shift. That would be with friction shifters. But I never dropped a chain that wasn't the result of a botched shift, damaged chain or damaged chain ring.
We did have a lovely CF LeMond with SRAM Force on clearance that would not stay sold because the front derailleur never shifted well. This was before Red, so it was top-drawer. Finally, we figured that somehow the carbon crank spider was bent. We swapped the crank and made someone very happy.