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I wrote this up for the long distance riders mailing list about a year ago. It explains how the Dyna Beads and similar tire balancers work:

Picture a wheel on an axle that can go up and down. Imagine that the wheel is out of balance, with one part of the wheel heavier than the other. (If you were going to attach weights, you would put them on the side opposite the "heavy" side.)

Now, picture that wheel spinning, out of balance. As the heavy side goes up, it "pulls" the wheel up with it. The axle goes up. As the heavy side goes down, the axle goes down.

Now, drop some freely floating beads inside the tire. The beads have inertia. As the wheel rises up on the axle, the beads (with their inertia) want to stay put, just as the bottom of the tire rises to meet them. This means that they migrate to the bottom of the tire at the same time as the heavy side is reaching the top of its rotation. Likewise, as the wheel goes down, the beads want to stay up, "floating" to the top of the tire when the heavy side reaches the bottom. As the wheel vibrates on the axle, the beads' inertia tend to distribute the beads opposite the heavy spot, in a way that balances the wheel and tire on the axle and dampens vibration.

As long as the wheel is in balance, centrifugal force will hold the beads in place around the tire, keeping the wheel in balance. If the tire vibrates due to imbalance, the beads will come off the tire wall, and their inertia will help them redistribute themselves to put the wheel back in balance.

At least that's the theory. That said, I wouldn't want Dyna Beads in my wheels. They aren't balanced when you start out, and I don't want to think about ceramic beads bouncing off the internal TPM sensors. Besides, my gut tells me that ordinary weights are a better solution. Weights are a compromise, and so are Dyna Beads, but I prefer the compromises of using weights.
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