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OK, I'm gonna lock this thread, feel free to start another one if you feel the need...

The burden of proof is on the claimant, you are claiming flex stays are creating increased axle movement due to the extra flex, therefore you must be the one to present the data. Your exact claim is, because i said so, my ass can feel it. There are experienced engineers here telling you they haven't seen it in making real bikes. So the burden of proof rests on you to prove YOUR claim.

If we’re now moving the discussion on to braking then that’s a completely separate thing and just as we can’t lump all four bars, faux bars, flex stays, etc together; nor can we brake designs. I don’t feel attacked, that’s okay. Trolled maybe. And it’s not a funny way to say anything, it’s first hand experience. I get many queries from riders about the flex stay arrangement of my frames. Folks are rightly or wrongly concerned about flexing elements of their frame. I’m always pleased to explain that the degree of flex is so small that it’s insignificant to the...

FWIW carbon fibre damps a lot more than metals. And a handlebar can also be somewhat damped 😉 Aaaand I'm out. I think we ran the course of the debate and are spinning in circles.

No need to do that.

Stable Ad? Stab Lead? how are we supposed to read that?

Using weed based composites in vehicle production is nothing new, they were doing it years ago. 🤣

I was working in the engineering department at Specialized during the whole "zertz" thing. They did absolutely nothing. We tested frames with them and without them on an MTS test bed as well as having strain gauges/etc and DAQ systems on for riding. They did not damp or mute anything, zero difference. The shape of the carbon stay itself did change how the rear end behaved when compared to a "normal" seat stay, but the zertz did nothing. It even got to the point where Specialized was ordering field test frames without them as the cost was a bit lower...

The strange behavior at the shock you can see there is due to the tire. In my opinion most, if not all, the suspension performance gripes that people have with flex stay bikes is mostly due to the fact that they are typically less gravity oriented so suspension performance for descending is not prioritized. The Stumpjumper 15 and the Stumpjumper 15 Evo are the same bike. In the previous Stumpjumper generation, the flex stay Stumpjumper was very different from the rest of the Stumpjumper models.

That's great and now I get it; thank you! I brought it up and your description of how I was thinking about it is correct; really appreciate all the thoughtful responses and discussion here.

Carbon can some impressive stuff, not too worried about a few mm of flex