There is no force available to make beads inside a tire move to a specific point 180 degrees from the source of imbalance. In fact the same force that keeps water in a pail swung around your head would force the beads to the point of maximum displacement; making the problem worse. Whether the point of displacement was static (out of round) or dynamic (unequal mass distribution).
It is only the fact that the beads possess insignificant mass relative to the mass of the tire and wheel and that they spread them selves out over the inside inside of the tire that they (dyna beads) generally do not cause a significant worsening of the vibration at speed.
This coupled with incompetent people balancing the tire with weights and the fact that modern tires are significantly better balanced then they were even a decade ago and will often run well without balancing weights reinforces the placebo effect which perpetuates this mythology.
Just the thoughts of an old engineer who balanced systems up to 20,000 rpm... Our tires rotate about 1120@80mph...
Like all myths, there is a kernel of truth to the lie.
Here is how it works, via a thought experiment:
The system must be free floating. A fixed system like a ship gyro or a jet engine will not work, it will rip itself apart before balance is achieved.
Think of a string, with a 1 oz weight on one end and a 1.25 oz on the other.
Attached to the string, where it can be moved about, but is fixed for any test, is an axle with enough length and flexiblity to act freely in 2 dimensions.
For this test, it is centered.
Apply a rotation to the axle. As it speeds up it will oscillate from our frame of reference. The string will spin around it's COG, not the axle.
Now, extend that to a tire, where the tire is free to move up and down the front fork. For this test the springs and oil have been removed and replaced with a magical friction free fluid. The wheel is free to move up and down.
The tire is somewhat out of round for this test.
Spin it up, and the wheel will oscillate around the COG, moving the axle/wheel with it.
Now add the beads to move freely around the tire.
The oscillating wheel is not a circle anymore, it is in effect a parabola, and the heavy side is the top and the light side is the bottom. Beads will flow towards the bottom and the oscillations will dampen until a dynamic balance is achieved.
QED
Here is the rub: the road is not a thought experiment. For one thing, you have the damping of the front shocks limiting the movement of the wheel.
The beads would have to constantly reconfigure and significant input, like hitting a pothole, will require the beads to reconfigure to achieve dynamic balance. Speed changes would do the same thing as acceleration or deceleration is in effect a change in the gravity vector.
During the reconfiguration, the wheel is by definition out of balance and oscillating
Given enough input, the beads may never reach a dynamic balance. One such scenario would be turning, hitting rough surface in the turn.
During that time the wheel would very likely be out of balance and be providing incorrect feedback to the rider.
Incorrect feedback increases the chances the rider may take the wrong corrective action, or fail to take corrective action. In other words, an "accident" that is anything but an accident.
Truck companies use another product called "Centramatic" that is like Dyna Beads but more sophisticated. It includes a track filled with oil, which would prevent "reconfiguration" from happening on every little input.
Here is a link to a "demo" showing how it works:
How Centramatic Balancers WorkWith 18 wheels, that seems reasonable if one set gets out of balance it is no big deal. If one of my two tires gets out of balance... not so good.
So I will stick with properly balancing the tire using fixed weights.
