here's another person claiming he's a engineer. and pretty much said what I was saying. I'm a mechanical engineer and here's what I know about the physics involved. As the wheel spins, the beads are going to be propelled outwards via centrifugal force. If there is any one spot on the inside of the tire that is further away from the center (axle in this case), that is where the beads would end up. Given the modern tire manufacturing makes for are very uniform tire, I don't think there is such a spot, unless it's a really cheap, crappy tire. (On a side note, modern tires are so well made that when you change a tire, you can typically leave the wheel weights on and it'll be very well balanced as the wheels are more out of balance than the rubber. It's been discussed at length here. Do a search). Now, if there is indeed an out of balance situation, the heavy spot on the tire is going to cause that spot to be pulled a little further away from the axle via the same centrifugal force and the beads will want to settle there thus increasing the out of balance situation. The physics of the system dictate that the beads should make the balance situation worse. On bigger vehicles, like trucks, the insanely huge mass of the tires is such that the beads have little noticable effect. I think that those who swear by them are suffering from the placebo effect. On a motorcycle, where the rotational mass is less and if the tires are perfectly (or very nearly so) round, my guess is that the beads distribute themselves pretty evenly as the tire gets up to speed and provide virtually no effect one way or the other.