Powder Wheel/Tire Balancing Problems

Recently put some bags of powder in my tires, the bags allegedly deteriorate and distribute a powder inside your tire. I've got 35" tires, so it was suggested that this technique (normally used by truckers and other large tire/high rpm applications) would work better than the normal balancing using weights fixed to the rim.

I can't figure out for the life of me exactly how this powder supposedly works to constantly balance the wheel, aside from basic inertial principles which don't seem to fully explain it. Anyhow, my conclusion is that it's not working so well thus far.

Initially alot of vibration at low speed right after I put the bags in (I assume it was before they had fully deteriorated and allowed the powder to be distributed). Went away within a couple of miles, fortunately I was able to drive fairly slow until then. Now, there's is random, periodic vibration at all speeds above 25 mph (i.e. the tires randomly become balanced/unbalanced).

Anyone have experience with this type of balancing? I'm aware of clumping due to moisture and/or freezing temperatures. Do I need to add a greater quantity of powder, or does this technique just not balance tires quite as precisely as normal balancing does?

Thanks,
ah