I should add that the term mass damper is a little misleading in the sense that they reduce oscillatory movements, usually comprising of two springs with a suspended mass between them, a sliding weight, that responds to g-loading or they can also be solid weights which are frequency tuned and fixed at one end. This device appears to be a combination of both in that it is principally an adjustable frequency resonator but it is designed to work on the unsuspended mass (in this instance the rear suspension) and specifically to compensate for the natural rebound/elasticity of any tyre under compression, where this is out of phase with the suspension causing changes in the trajectory of the suspension, that the suspension alone cannot entirely compensate for. Typically triggered when riding over a succession of bumps for example. Additionally, when ABS is activated it will help settle the rear of a motorcycle and any changes in the handling characteristics. There are several very informative and much more complicated explanations of the physics behind this device online (which are all in Italian so probably no point in me linking them here), but they do explain the fundamental reason why this works.
Scroll through this article quite a way and there is another explanation, https://www.motorsportmagazine.com/articles/motorcycles/motogp/motogp-mutterings-catalunya Andy
Interesting stuff Andy. TBH there are so many variables when it comes to suspension and the physics behind it. In actual fact the systems I typically come across in my day job are a lot less complicated to understand, as long as I stick to the fundamentals of how they work and why and not get too caught up in the science behind it!!
