Originally Posted by
Polaris OBark
I think the idea is that a flexible bike (or maybe more specifically, a flexible top tube) behaves like a spring, or an un-damped oscillator, and a stiff bike behaves like a highly damped oscillator (or a much more rigid spring).
A stiffer bike frame is modeled as a stiffer spring, but it doesn't necessarily have higher damping than a more flexible frame.