Originally Posted by
CliffordK
I like the stick or road debris hypothesis, but @
himespau has a good point that the stick would tend to cause more damage other than the point damage spot. Both seatstays? For a partial crack, one might see impact damage at the back, and opening at the front, so several different views of the crack would help.
I might expect centrifugal force to push the stick out to the rim. But the physics of it may be more complicated with the rim largely stationary with respect to the street.
And since it isn't completely sheered, either it stopped the rider cold, or whatever it was either broke, or fell out of the spokes.
Stuff happens fast and not all sticks are nicely uniform, so I wouldn't expect damage to be neat and symmetrical, either. Maybe it was thicker and stronger on one end. Maybe it was branched and the force more diffused on the other side. Maybe it was a long branch, only the tip got caught up, and the leverage from the rest of the branch was enough to crack the stay before it got flung behind. Maybe it went in cock-eyed, etc, etc. Any of that is more plausible than it just buckling in that manner while riding around.