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.
That's a hell of a fender brace! Look at the buckling of the downtube again. It is very deep (roughly 10% of the tube diameter). The tire would have mitigated damage from something as light as a fender bracket.
Originally Posted by
FBinNY
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.
The buckle doesn't have to be right behind the head tube and the fender bracket could have been enough of a nudge to make the top tube buckle there rather than further up.
Originally Posted by
FBinNY
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.
As you said above "That's a nice theory" but look at the evidence. You have a round down tube that isn't round anymore at a high stress point in
any bicycle frame. The bike has been in a
severe crash that damaged the forks...a very tough, strong part of any bike. I'll pose this question: Would you buy this frame and ride it? If not, why not? You said that a repair would outlast the owner and when it fails it would give generous warning.
I, personally, don't believe it would outlast the owner nor that failure would be slow.