I wrote earlier this week that my frame, a Cannondale Six-13, had cracked at the water bottle cage mounts along the seatpost.

I think I figured out why today. While taking it apart to send the frame to Calfee for repair, I found that the front derailleur had been mounted way too tight. The derailler caused the aluminum to compress (the frame is now shaped around the front derailleur), which I think put too much strain on the carbon tube that is molded to the shape of the aluminum.

The cracks that appeared after my crash, it seems to me, were innevitable. My crash just caused them to finally appear. This makes me feel better because I was concerned about how carbon could crack in such a light crash.

It is not uncommon for CF tubing to take on a slight indentation in the shape of clamp-ons. This can often be observed at the stem clamp area on CF handlebars. This does not constitue damage to the CF component. Calfee may be able to tell you if the tubing under the FD clamp was crushed.

If the frame hit cage first during a crash, it is not at all surprising that the frame would crack.

"It is not uncommon for CF tubing to take on a slight indentation. . ."

While that's true, OP said the aluminum tube to which the FD was clamped was indented (The Six13 has a carbon seat tube that joins to an aluminum extended bottom bracket area, I believe). Don't know for sure, but if the aluminum was compressed that much, the sleeve of carbon underneath (I assume that's how it's joined, though I don't know) could have been compromised, thereby weakening the whole carbon part of the seat tube. Conjecture only, but seems possible, if not likely.

Oops -- I missed the part about the damage being to the Al portion of the frame. Indented Al is a much different story.

Are you sure that the aluminum was not intentionally shaped (if the clamping area is in fact aluminum)? Many Al frames with oversize tubes have an intentional indention around the derailer clamp area to aid with clearance.

Are you sure that the aluminum was not intentionally shaped (if the clamping area is in fact aluminum)? Many Al frames with oversize tubes have an intentional indention around the derailer clamp area to aid with clearance.

The metal is buckled in the gap of the mount where the screw connects the front derailleur, which is why I don't think it is intentional.

The metal is buckled in the gap of the mount where the screw connects the front derailleur, which is why I don't think it is intentional.If that is true and you haven't adjusted the bolt then someone owes you a brand new frame.