Originally Posted by
FBinNY
...snip...
FWIW - your issue illustrates one of my pet rants against CF frames. There's nothing wrong with CF per se, but makers haven't given enough thought to real world hazards. We all know than chains fall of, or there's something called "chain suck" and whatever. So, knowing there's a reasonable risk of the chain "attacking th chain stay in that area, I'd expect (demand) some kind of ballistic layer to prevent damage. The added weight and cost would be negligible, but makers don't seem to care for their customers that much.
Yeah, dropped chains aren't built into the frame design.
My LBS added a
chain catcher to my new bike without asking me first, so they probably do this to all their new carbon bikes. The carbon frame is very wide down by the bottom bracket, and the gap between frame and crank tapers down to a slot narrower than a chain. So any dropped chain is going to jam in there and do some damage.
These catchers wouldn't prevent "chain suck", though.
Chain suck
The OP's damage does look like chain suck, since it's at the chain stay, not in front of the bottom bracket. This
chain suck article lists the causes:
Front shifting under heavy pedal load.
Worn chainring.
Chain maintenance.