Frame Flex on GCN

[Kontact]

Originally Posted by cachagua

Even if you could hold your leg that still, it wouldn't prove what you're trying to make it prove. The problem here is the same flaw that invalidates both the video and the FEA: they depend on the resistance at the rear wheel decreasing. That doesn't happen when you're riding.



Yes, people are suggesting that, but it's a misconception.

The flex in your frame does not ever make you go forward, period. That's because for this to happen, a lesser force would have to overcome a greater one. It is that simple.

As you're riding along, your legs vary how much force they're exerting between a maximum equal to (overcoming your inertia)+(frame flex), and some amount less than that. Now here comes the crucial point: your inertia never lessens.

The only time when the frame can un-flex is when your legs ease off, and the suggestion that when that happens, the flex energy is going to overcome your inertia -- the greater force, now that your legs are applying a lesser force -- is incorrect.

That is even vaguely true. The frame un-flexes when the load shifts from right to left. And that happens without the pedal forces going to zero.

What's getting left out of your analysis is that there are actually two ways for the frame to store some pedaling energy - by lowering the chainring (right pedal load), or raising the chainring (left pedal load). Moving between them is when the stored energy is pushed down the stays.


All the various static examples are demonstrating is that the flex is still in line with the drivetrain, and isn't just flying out into space. Then you take that understanding and apply it to the fact that the tension on the chain never goes to zero and the BB flex automatically alternates from right-to-neutral-to-left.