Please enlighten me.

[PK99TJ]

I keep reading these threads on that other board, regarding balancing tires with BBs. And, everytime I read it -- it sounds like so much physics witchcraft to me. I don't understand how this could possibly work, but "everyone" just knows it does.

It would seem that a perfectly balanced tire would have the centrifugal force outward (or the centripetal force inward) in balance everywhere around the circumference of the tire (points 180 degrees from each other centrifugal or centripetal force is mass x velocity (squared) / radius)...

A tire with imbalance potentially has a bit more mass on the tire in some part of it so the centrifugal force is greater there than directly oppposite that point on the other side of the tire.

When the tire spins, the centrifugal force would change the shape of the spinning tire ever so slightly, making the effective shape a very very subtle egg shape. (Of course tires can also be out of balance laterally... let's ignore that part).

The BBs would then collect in the area with the most mass, because in addition to the centrifugal force acting upon them, they now would require additional force to leave this area of the tire (effectively rolling up a hill, or out of the valley created by the extra mass).

I can't seem to think of any reason why the BB trick would work, but then again -- I don't have a degree in Physics. Maybe one of you do.

?

Patrick

[mrblaine]

I can't help you with the tires Patrick, but I do know there is a ring shaped tube around the top of washing machine tubs that is partially filled with a liquid. It performs the duty of controlling the tub's oscillations when it reaches an out of balance situation with wet clothing.

Works fairly well if you think about it. How difficult would it be to toss random weight clothes in something and then spin it and have the owner figure out how to load them in there correctly enough every time to not shake the machine across the floor and out the front door?

You would probably have to take a class in tub balancing at the local Jr. College to own a washing machine.

[PK99TJ]

Hmm, that definitely seems to be some sort of counter example that it is ALL witchcraft. Now I'm more confused. My guess is that the washing machine works because the counter weight is at the top, and the weight is at the bottom. What it actually is balancing is a slight angular movement created by spinning socks and underwear, so that the tub from a side view looks more like


water======
.\\\\\\\\\\\
..\\\\\\\\\\\
...\\\\\\\\\\clothes


(ignore the .'s)

If you draw a straight line up and down to mark the spindle, the balance (overall) is maintained. For the top half, you can see that the water would actually collect to counter balance the clothes for the same reason I suspect the BB stuff is bunk. There's now more mass (via the tilted tub) therefore more centrifugal force.

Just a guess?

[TObject]

Just so there is no misunderstanding, when you are talking about BBs, you mean bowling balls?

Looks like somebody have never experienced the thrill of race between a washing machine and a dryer. Go washing machine, go!!! ? Go dryer!

[TJRON]

Maybe this will help?
http://wheelweights.ca/balancing-beads-how.htm

http://wheelweights.ca/balancing-beads-chart1.htm

[PK99TJ]

Well, they do say that it won't work on a wheel balancer. At least I agree with that part. Why it works otherwise, I have no idea. That's good enough for me though, thanks.

[Art Welch]

Here is an explanation although I can't attest to accuracy:

http://www.balancemasters.com/howtheywork.html

It seems reasonable that the behavior of BBs in a tire would approximate that of the fluid in the Balance Masters ring.

[TObject]

Quote from that article: ?American engineers perfected the idea in the late 1930's and early 1940's when they needed to find a way to perfectly, precisely and continuously balance a new-fangled invention...the jet turbine engine.?

Nothing like this is used to balance jet engines these days.

They say, ?The Balance Master is a tested and proven device which works on long understood and basic engineering principles.? If somebody could point me to the resource that explains those principles, that would be great.

I do not understand their statement ?Centrifugal Force holds the fluid in that position?. The centrifugal force doesn?t hold anything; it tries to rip the wheel out of the hub. Actually, centrifugal force doesn?t really exist; we just think that it exists, for convenience...

I can imagine where there can be theoretical solutions on how far from the center of the tire to position such a mercury filled ring tube, depending on the size of the wheel, weight distribution on the wheel and rotational speed; but I can?t see how can there be one universal device to fix all vibrations.

Again, I am not even trying to understand how these balancers work. I am trying to say that if they use ?long understood and basic engineering principles?, then come on, let?s see those principles explained, let?s see patents, publications, anything...

[speaceman]

Brushing the dusty cobwebs off of what little I remember of the college physics course I took, the only thing I can think of when it comes to "well accepted engineering theory" is maybe the following:


Perhaps the ball bearings generate a force in an outwards direction which counters the inward force generated by the cetripedel motion of the tire.

How this affects balancing, I do not know. I'm guessing maybe the force inwards is reduced equally over the interior of the tire (I'm assuming the bearings spread out as the tire spins) thereby dampening occillations/vibrations or something????

That's all I can muster with out suffering a brain annurism. Anyone have the number to their high school physics teacher?

[Dan-H]

Originally posted by TObject
Actually, centrifugal force doesn?t really exist; we just think that it exists, for convenience...

Actually, I don't really exist, I just think I exist for convenience...



recall from physics that if you attach a string to a ball and swing it in a circular manner, then the force that is required to keep the ball moving in the circular path is called the centripetal force

the centripetal force is directed inward, towards the axis of rotation

as you swing the ball with the string, you feel the string tug on you hand...., this is called the centrifugal force and is equal and opposite to the centripetal force...




http://apollo.lsc.vsc.edu/classes/me...apter9/cg.html

[Art Welch]

Patent # 6,267,450 seems to cover their device. I haven't read it, but here it is:

http://patft.uspto.gov/netacgi/nph-P...1&f=G&l=50&s1='6267450'.WKU.&OS=PN/6267450&RS=PN/6267450

[Dan-H]

"well accepted engineering theory" means I'm too lazy to look up the original reference to be certain I have it cited properly

When presenting, hand waving is typically appropriate for the proof...

[speaceman]

I just read the link in the above post and I guess it makes more sense.

You are going to have a stronger centripedel force generated at the imbalance, so the fluid or the bbs flow the side opposite the imbalance to counter the force, since the centripedel force should be equal with all factors remaining the same as the tire spins.

Does that make sense?

[PK99TJ]

Originally posted by speaceman

Perhaps the ball bearings generate a force in an outwards direction which counters the inward force generated by the cetripedel motion of the tire.

If you look at that formula that I posted way up there, what the BBs do to the formula is to add more mass, thereby balancing the added mass on the opposite side.

What baffles me is how the BBs "pick" their final locale. Of course there is some physics to the picking, but I have no friggin' idea about that part.

But it is something "everybody knows" works.

[PK99TJ]

Originally posted by speaceman
I just read the link in the above post and I guess it makes more sense.

You are going to have a stronger centripedel force generated at the imbalance, so the fluid or the bbs flow the side opposite the imbalance to counter the force, since the centripedel force should be equal with all factors remaining the same as the tire spins.

Does that make sense?

This is how everyone assumes that it works. Now, if you reread my first post, see if you can understand my objection to that theory.

[PK99TJ]

Sorry I did this is Word. :P

This is why I believe them when they say that it doesn't work on a wheel balancer.

The diamond is the axis of rotation. The smiley face (sorry, again...) is additional mass that needs to be balanced somehow. The top pictures shows not rotating, the middle pictures show rotating, the final pictures show where the BB's would go.

I can see clearly from this why on a wheel balancer it does not work right. What I don't get it why it DOES work right on the road. What changes?

The diagram is clearly exaggerated on purpose. If your tires really stretched out that much, you'd have to rotate your kidneys as often as you rotate your tires.

[Dan-H]

I wonder if we are confusing balance with out of round.

both can cause vibes.

no amount of weight can fix a tire that is not round.

I can't explain why BBs or equal or golf balls supposedly work.

- Dan ( thinking maybe the sun orbits around the earth afterall )

[PK99TJ]

That's okay, it's been a productive discussion anyway, much moreso than the other board, where it isn't acceptible to wonder why something like this even works.

I think the diagram someone posted over there regarding how Equal works is telling though. Notice how they list "equalizing mass" last on their checklist of why it works, favoring instead the dampening effects of BBs when hitting the flat side of the tire on the road surface.

I have no idea how that would even look, without a simulator or some translucent tire... but it definitely adds enough variables in my mind to stick with weights.

Imagine all these people now pouring BBs into their tires. I'm sure there has got to be SOME effort made to trying to understand how much weight is really required rather than just going with the 4oz-6oz suggestion.

Moreover, some people, after seeing that they have 6oz of weights on their wheel, decide that 6oz of BBs must be right... clearly overlooking the fact that the effect of the added mass is also effected by the radius. Just ask a figure skater.

Oh well. I've hit a brick wall on this one. Without seeing how BBs jump around when they hit the road surface edge, it will remain physics witchcraft to me.

[PK99TJ]

Okay, Overtech posted this on that other board, and I am quoting it because it:

a) Agrees with me completely
b) Makes sense (see (a))
and
c) Explains what I was trying to say with my diagram, only better.

This is NOT MY ORIGINAL WORK, this is from a Jeep mailing list:

According to Newton's second law Force = Mass x acceleration. Torque is a rotational force: Radius x force.

When a body is in Equilibrium, the vector sum of all the forces is zero, and the body will remain at rest, or if moving, it will maintain a constant velocity.

Since we are talking about a tire, which travels in a circle, we say that in order to achieve Rotational Equilibrium the sum of the torque must be zero.

The following is info from the Motor & Equipment Manufacturers Association explaining how the bb's themselves work (or might not work as you can see from the last paragraph):

Moveable weights and internal tire balancing compounds (TBC), in theory, can correct states of imbalance based on the several laws in physics. In a free state, the center of rotation of a spinning body will always be the center of mass of the body. In a perfectly round and balanced rotating assembly, the center of rotation is the same as the center of mass and geometric center.

If, in a free state, the mass of one point is increased on a spinning circular assembly, the center of rotation will move toward that point until the center of rotation is coincident with the new center of mass. If a moveable weight is introduced to this free spinning body, centrifugal force will force the weight away from the center of rotation.

If the center of rotation is not coincident with the geometric center of the assembly, then a moveable weight will, by centrifugal force, be pushed to the section of the assembly farthest from the center of rotation. Thus, with the assumption that the part of the assembly closest to the center of rotation is the heavy side, the moveable weight will migrate to the light side of the system. Within this context, the system becomes balanced.

This theory for balancing has been developed in a free state and is dependent upon the center of rotation being distinct from the geometric center of the tire. If the migration of the center of rotation of a tire is restricted by introducing an axle and suspension system, the center of rotation is no longer free to move towards the center of mass.

As all rotation is around the axle, the system is constrained and the center of rotation fixed at a point that is not likely to coincide with either the center of mass or the geometric center of the system. Additionally, dimensional irregularities may have no direct correlation with irregularities in mass. When normal manufacturing tolerances are coupled through three different units ? the spindle, the wheel, and the tire ? these effects are compounded. Adding all of these together, not only is it unlikely for one of these alternatives to actually balance the system, some of these methods could actually add to the total imbalance. Furthermore, because the weight of the vehicle distorts the shape of the tire, the tire geometry is constantly changing as the vehicle travels down the road, and the distance from the center of rotation to the light side of the tire is in constant flux.

Dave

Now I am satisfied.

[Blatant]

Sounds reasonable. ****, who am I fooling? I only understood about every third word! LOL.

BUT, I run four golf balls in each of my 38.5 SX with no other balancing and they seem to work pretty well in the limited street driving I do.
Dion