Originally Posted by
FBinNY
This is a nice theory, except that it disregards all the physical evidence. The shape of the dent shows that it's a dent, and not a buckle. Moreover it's precise alignment with the fender brace, stretches credulity as a coincidence. What almost certainly happened is the fork pushed back pushing the wheel into the downtube with the fender brace trapped between them.
In any case, when downtubes buckle from front impacts it's almost always at the bottom directly behind the headtube. The reuslting buckles have a characteristic appearance (clearly a buckle) which this frame doesn't.
As far as safety goes, without any repair at all this frame has a decent chance of outlasting it's owner, and if and when it fails will give generous notice.
I really appreciate all the responses I've gotten. I'm not claiming to be an expert at this, but I have stared at the frame and thought about it a great deal, and I'm convinced it's a buckle. There is a crease that cuts across the frame at 90. It's not a round or oval dent that might be caused by something pointy hitting the frame. The fender strut looks to be in pretty good shape, by the way. That could have buckled if there was a hard collision between the frame and the strut.
I'm scrapping the frame. I freely admit that I could be wrong about whether that is really necessary. However, I figure if there is even a 5 or 10% chance that the frame is unsafe, it's worth spending the bucks to replace it. (I'm probably buying a $200 Fantom CX frame from Bike Island + LBS labor). I feel I got off lucky this time. Broke the foam in the helmet, but avoided a concussion. My knee is hurt enough to miss probably 3+ weeks of cycling, but at least the doctor thinks there are no torn ligaments or tendons. Next time could be worse. So maybe I'm wasting money, but I'll least I'll have a little more peace of mind.
Thanks everyone!