Originally Posted by
spare_wheel
3 of the 5 metal frames I've owned that have failed did so due to fatigue or imperceptible accumulated damage. I personally would never ride a frame with that much structural damage without a repair. Dents or blows that visibly deform tubing induce stress risers that will severely compromise strength.
All the steel frames that I have broken failed at either the seat tube/bottom bracket junction (two, one a tandem) or the seat tube/seat stay junction (three). I have a '76 Trek with a very similar dent to the OP that has seen some hard usage, but I wouldn't consider such a dent to have structural implications since I have never seen a top tube fail. Does this really happen?
I would think that the heat stress of replacing the top tube on the seat stays would leave the bike more likely to fail, but I'm biased by the failures I have caused.