Originally Posted by
McBTC
Interestingly enough, as I understand it, 'stiffness' has to do with how far something can be flexed before it breaks or is permanently deformed because it is no longer able to return to it's original state. So, when you look at it in that way, flexing the frame as the kid did wouldn't cause any permanent deformation because in the range we're talking about, the stiffness of the bike's frame (overall at least and not necessarily at the joints) is more like a compliant rubber band than a stiff and brittle toothpick.
Sorry your thinking is wrong. Stiffness is unrelated to how far aka displacement something can be flexed before it breaks.
Like all stiffness threads, the nay sayers always come out and say a flexible frame is as fast as on that is laterally stiff which is nonsense and the reason every single bike company tries to make their race bikes as laterally stiff as possible. There is no exception...thousands of engineers that make up the bike industry are in uniform agreement. All anybody has to do is climb a hill on a SL2 Roubaix and then a SL4 Roubaix which climbs like a Tarmac...night and day...same 2D geometry.
People tend to think of a frame as one that stores energy consistently. Powering a bicycle at 20 mph is the integral of hundreds of small accelerations making up the pedal stroke comprised of power zone and dead zone. Anybody who has ever ridden an uber stiff race bike knows they out accelerate a whippy bike.