I was going to post this on Tires section, BUT...

[Darsus]

...This may be of interest to my new friends here. I am a securities analyst/fund manager for an independant firm out of Salt Lake City. One of my targets a year and a half ago was the tire industry, specifically, how Firestone was fairing after their Ford Exploder debacle. I found that tire manufacturers go out of their way to have tires leave assembly with NO imbalance. Think of it, if something the weight of a tire, with a couple of tons riding on it, spinning at thousands of RPMs the more out of balance, the more likely it will be to fly apart. My point? Why pay the extra $15 per tire to have tires balanced? IF the rims are out of round, balancing won't cure it. Are we just being sheep, thinking that balancing now-a-days is neccessary?

[Wheelspeed]

Well, they try to have no variance in thickness and shape, but there is always an acceptable tolerance.

The actual rim may need a little balancing also, so I don't know if you NEED to if you think your rims are perfect, but I'll definitely still be getting mine balanced.

[Reaper]

First of all, balancing is a deep topic. Lets say that tires are balanced well from the factory, thats all fine and dandy. Maybe they are, maybe they are not. Their diameter, materials of construction and manufacturing methods are all obstacles to getting a truly balanced priduct to market, but lets say they do.

The wheels are a completely different story, particularly if they are cheap wheels.

There are two methods of balancing rotational components, single plane and dual plane balancing, or static and dynamic methods.

The deciding factor is their width to length ratios. if an item has a width that is 1/7th of its diameter or less it can be effectively balanced using single plane methods generally speaking.

If it has a lesser ratio, say its width is 1/4 of its diameter it must be balanced using the two plane balancing method.

The single plane method can be likened to mounting the wheel/tire combo onto a shaft that sticks out from both sides of the wheel, and then placing that shaft on a set of knife edge rollers. You simply allow the wheel to rotate until the heavy spot is on the bottom, and install a compensating weight 180 degrees from the heavy spot. That weight can be placed anywhere along the width of the tire and it will have the same effect. You are basically counteracting the effect of a single mass of imbalance in the radial direction.

This is in fact how most wheel balancers work, but they do rotate the tire to find the exact angle of the imbalance, a more precision method than simply letting the wheel rotate on its own account.

However, and this is what is not generally understood by the public. There are two imbalances to deal with in a wheel/tire combination, both static, as discussed, as well as dynamic.

Imagine a 1 inch diameter rod about 3 feet long and straight, that rod has perfect balance when rotated. Now place an offcenter weight exactly at 1.5 feet from one end. Now that rod has static imbalance. That weight will try to move the entire rod off its axis evenly across its length in the same direction.

Now remove that weight and get another one just like it. Place one of the weights on one end of the rod at zero degrees, and at the other end, place the other weight 180 degrees from the first. Now when you rotate that rod, one end wants to go in one direction while the other end wants to go into the opposite direction. This is dynamic imbalance and it cannot be removed by placing weights on a tire in the same plane across the width of the wheel. To remove this imbalance one must compensate for one imbalance weight at one end of the rod with an equal weight 180 degress from the original imbalance and then go to the other side of the rod and do the same thing. This is simplified as the two counterbalance weights have little interaction.

Wheel/tie combos are similar , a weight on the inside of the wheel and a weight on the outside of the wheel , but since the imbalances are not necessarily 180 degrees as in the simplified example above, some care must be taken as to how the two weights affect the other planes balance.

if one does not do this, either when the wheel is manufactured or during wheel/tire balancing , you will leave some sort of dynamic imbalance in the item. This imbalance is dynamic, and it will cause the wheel to move back and forth as it tracks down the road, perhaps so violently that the tire materials internally shear from the stress. NO , its not a big problem unless there are some other more primary faults such as in the manufacture of the tire, but it is there.

it is also worthy to note that there are no actual standards and methods for wheel balancing that must be adhered to. Even in industry there is no such thing. many parts that actually require dual plane balancing are routinely balanced only statically, pump impellars in particular. Sure they last a year, but the bearings go out soon after that, and then the warranty is over.

Wheel manufacturers should dual plane balance their wheels prior to final finishing, that would be the ideal solution. How many do actually dynamically balance their wheels? I dont know, but I suspect only the very best wheels ge tit because it is not cheap to do.

I have a hard time believing that tires are very well balanced dynamically at all. The greater the diameter of the wheel the greater the effect of any equal weight imbalance will be, and as the wheel speed increases, that exponentially increases the imbalance forces generated, both being functions of centrifical force equasions.

Conclusion: ALWAYS get your new tires balanced, its far far better than not doing it. You can at least take out the static imbalance of the wheels that way.

[Skipper5]

I have a hard time believing that tires are very well balanced dynamically at all. The greater the diameter of the wheel the greater the effect of any equal weight imbalance will be, and as the wheel speed increases, that exponentially increases the imbalance forces generated, both being functions of centrifical force equasions.


WTF is the "centrifical force equation?" :confused

[bähnstormer]

that's a typo hehhehe!

[Darsus]

First of all, balancing is a deep topic. Lets say that tires are balanced well from the factory, thats all fine and dandy. Maybe they are, maybe they are not. Their diameter, materials of construction and manufacturing methods are all obstacles to getting a truly balanced priduct to market, but lets say they do.

The wheels are a completely different story, particularly if they are cheap wheels.

There are two methods of balancing rotational components, single plane and dual plane balancing, or static and dynamic methods.

The deciding factor is their width to length ratios. if an item has a width that is 1/7th of its diameter or less it can be effectively balanced using single plane methods generally speaking.

If it has a lesser ratio, say its width is 1/4 of its diameter it must be balanced using the two plane balancing method.

The single plane method can be likened to mounting the wheel/tire combo onto a shaft that sticks out from both sides of the wheel, and then placing that shaft on a set of knife edge rollers. You simply allow the wheel to rotate until the heavy spot is on the bottom, and install a compensating weight 180 degrees from the heavy spot. That weight can be placed anywhere along the width of the tire and it will have the same effect. You are basically counteracting the effect of a single mass of imbalance in the radial direction.

This is in fact how most wheel balancers work, but they do rotate the tire to find the exact angle of the imbalance, a more precision method than simply letting the wheel rotate on its own account.

However, and this is what is not generally understood by the public. There are two imbalances to deal with in a wheel/tire combination, both static, as discussed, as well as dynamic.

Imagine a 1 inch diameter rod about 3 feet long and straight, that rod has perfect balance when rotated. Now place an offcenter weight exactly at 1.5 feet from one end. Now that rod has static imbalance. That weight will try to move the entire rod off its axis evenly across its length in the same direction.

Now remove that weight and get another one just like it. Place one of the weights on one end of the rod at zero degrees, and at the other end, place the other weight 180 degrees from the first. Now when you rotate that rod, one end wants to go in one direction while the other end wants to go into the opposite direction. This is dynamic imbalance and it cannot be removed by placing weights on a tire in the same plane across the width of the wheel. To remove this imbalance one must compensate for one imbalance weight at one end of the rod with an equal weight 180 degress from the original imbalance and then go to the other side of the rod and do the same thing. This is simplified as the two counterbalance weights have little interaction.

Wheel/tie combos are similar , a weight on the inside of the wheel and a weight on the outside of the wheel , but since the imbalances are not necessarily 180 degrees as in the simplified example above, some care must be taken as to how the two weights affect the other planes balance.

if one does not do this, either when the wheel is manufactured or during wheel/tire balancing , you will leave some sort of dynamic imbalance in the item. This imbalance is dynamic, and it will cause the wheel to move back and forth as it tracks down the road, perhaps so violently that the tire materials internally shear from the stress. NO , its not a big problem unless there are some other more primary faults such as in the manufacture of the tire, but it is there.

it is also worthy to note that there are no actual standards and methods for wheel balancing that must be adhered to. Even in industry there is no such thing. many parts that actually require dual plane balancing are routinely balanced only statically, pump impellars in particular. Sure they last a year, but the bearings go out soon after that, and then the warranty is over.

Wheel manufacturers should dual plane balance their wheels prior to final finishing, that would be the ideal solution. How many do actually dynamically balance their wheels? I dont know, but I suspect only the very best wheels ge tit because it is not cheap to do.

I have a hard time believing that tires are very well balanced dynamically at all. The greater the diameter of the wheel the greater the effect of any equal weight imbalance will be, and as the wheel speed increases, that exponentially increases the imbalance forces generated, both being functions of centrifical force equasions.

Conclusion: ALWAYS get your new tires balanced, its far far better than not doing it. You can at least take out the static imbalance of the wheels that way.

I didn't want to get us into a debate on Quarks and electron rotationary laws, but how can a wheel, manufactured these days, be out of balance? True, it can wobble out of round, but balancing won't help that. And I have seen the process of making wheels, any welds are ground smooth, there arent thicker parts on one side of the lip, than another.

TIRES? Same thing. with the processes now, and the potential for catastrophe, they can get the tire just about perfect. THEY TOLD ME SO! That's my fkn point to even bringin it up. And sure enough the guy named "wheelspeed" (denoting a connection to tire/rim sales) chimes in with "you should balance them"! I'd say save the $62 for the balancing. To most here $61 isn't a big deal, it just PEEVES me. It's kinda like McDonalds having a "heater charge" in the winter, and Footlocker charging a "Fitting fee". You know why tire companies do it? Because we allow it. If you bought a car, and the steering wheel wobbled as it turned, you'd take the car back. It's 2005, we are cloning animals, tell the tire guy to eat the phoney "boogy man tire wobble insurance". And if the tires he/she sells you vibrates, take em back for a better set.

"Hi I'm Joe, I'm going to sell you a product that is not perfect from the factory, AND I am going to charge you for your satisfaction. "

[bähnstormer]

the density of the metal isn't the same everywhere.

[Darsus]

Are you suggesting that there are air pockets in the forging? Because metal is metal.

[Skipper5]

am i simplifying things too much if look at this strictly from an angular momentum stance?

also, no wheel or tire is perfectly round, its the simple nature of things. to some tolerance (i.e. +/- .001") you will always have imperfections. i would agree that metal is metal, but its still not perfect in macroscopic shape.

bahnstormer, even if that is just a typo for centrifugal (not centrifical) i still want to know which equation he is talking about.

[Reaper]

Skipper 5,

No your not simplifying it. You have gone too far with it, back up a bit and stick with the straight in and out forces of circular motion. Your angular momentum thinking is more appropriate for banked turns and such, this is not that far along circular motion, but an understandable diversion.

An imbalanced mass, when constrained to rotate about a fixed axis generates a force of imbalance according to the formula,

F = mass x (velocity)squared / radius of imbalance mass from rotational axis.

Thats the basic centripetal force equasion. Since the imbalanced mass is constrained to rotate about a fixed axis, this formula also expresses the centrifugal force the imbalanced mass exerts. Apply the first and third laws of motion to this.

First law says, a body which is neither stationary nor moving along a straight path at constant speed is being acted upon by a force.

Forget for a moment that the mass is attatched to a body. Imagine you are holding a string with a weight at the end of it and you spin it overhead. Some force is acting on that mass keeping it moving in a circle, its acting to push the mass into a circular motion, thats an inward force ( centripetal force ) along the string. It can be represented as a force vector pointing inward from the ball. Also, there is another force that you feel as the pull on the string. The pull on the string is the centrifugal force. This force is equal and opposite, according to the third law, and can be represented by a force vector of equal magnitide as the other one, pointing from your hand outward to the mass at the end of the string. Equal and opposite forces or reactions.

From the equasion you can see that the velocity is squared in the numerator. Increasing the speed has a more dramatic effect on imbalance forces than increasing mass.

Darius,

It's one thing to see a process, its something else again to actually know what you are seeing.

For one thing, theres nothing guaranteeing that each spoke of a forging is the same thinckness, nor of the same exact shape, unless all the surfaces of the wheel are all machined on a CNC equally, and that my frind is simply not the case for all but the most expensive wheels made, and even then , its probably not true. Forging is a very rough process, and typically requires some sort of finishing, grinding buffing, whatever. If its done by hand , then I guaranttee you the wheel will not be balanced, and even if they have some sort of polishing machine, it still wont help. And yes, most likely there are many places arund the wheel that are not the same thinckness that should be.

You sound incredulous that a forging might have internal defects or voids. Why is that? It cetainly is possible and it doesnt mean for a second that part will necessarily break. But it does affect the balance of a finished product.


And for your information, this has not a thing to do with Quarks or electron rotational energies or forces necessary to rip them from their orbits, which by the way, is 34 electron volts. It has everything to do with simple mechanics and answering your initial question about balancing.


have you ever seen a new cars wheel/tire assemblies?

They all have balancing weights on them. ALL of them. If your assertion is correct, that we dont need to balance, then by default we are all driving on imbalanced wheel/tire combos right now. That is a logical conclusion based on your assertion that wheels are balanced in their production and tires are as well. So tell me, why would a car manufacturer have balance weights on a new car? To purposly build in imbalance into the wheels?

And what about if a car throws a balance weight while driving? If they indeed are necessary, and one is thrown, you wouldnt know it with your theory about sending the tires back and demanding new ones.

I think your only about half done with your analysis, and the conclusions you have to date are severely in error.

[Skipper5]

Thats the basic centripetal force equasion. Since the imbalanced mass is constrained to rotate about a fixed axis, this formula also expresses the centrifugal force the imbalanced mass exerts. Apply the first and third laws of motion to this.

First law says, a body which is neither stationary nor moving along a straight path at constant speed is being acted upon by a force.

okay, i just lost all respect for what you have to say. you don't seem to even know how to state Newton's First Law correctly which i will state now: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

what you said does not take into account a non-stationary object traveling at constant velocity (that is if i'm reading your description correctly). part of physics is being able to explain something clearly; you fail here with something very simple.

and i think newton's second law is better used:
Force acting on an object = the sum of the changes in linear momentum

OR when mass is constant simply: Force = mass*acceleration

oh and how wonderful that in this case acceleration = v^2/r and gives us:

F = mv^2/r

take your stupid "centripetal force equasion"(sic) and educate me more!


btw, my friend wanted to know where you earned your BS.

[Skipper5]

when i said angular momentum i should have taken it a step further mentioning Euler's Laws. namely that the sum of the moments = angular acceleration (which is derived from angular momentum remembering that H = I*omega) this is moving even closer to gyroscopic motion with steady state procession: the out of round mass will put a torque on the shaft and thus will cause the wheel to "wobble"

[Dan]

do you know how hard it is to make a PERFECT circle and i mean PERFECT, not visually but to spec? Toyota came out and said they can do that like 10 years ago and the engineering field raised eyebrows on this news. My dad's a mechanical engineer so he knows all this whoopla. now knowing how hard it is to make a perfect circle, what makes you think they can make a tire prefectly and not out of round or off balance? visually everything looks 10/10 but when you so spec'ing it out, you'll find more imperfections than you think,

[Nerf26]

If you dont balance and you have a vibration, its back to the tire store and thats a pain in the ASS!

Regardless of RIM or TIRE imperfections, those dynamic tire balance machines (assuming there are setup properly) dont lie...add some weight and spin it again...then its done.

so whet ever the reason...BALANCING IS GOOD.

[Reaper]

OK Skippy,

Since you seem to be in a disrespectful mood I will address you in the same manner. It's clear from your answer you are nothing more than a first year engineering student with a very limited understanding of the english language and a clear inability to deal with word problems or explanations.

I've been doing work like this for one hell of a long time and your opinion doesnt change the fact that the equasion I gave works now and will work for as long as the laws of physics dont change.

The first law , as I stated it, came from a high school physics book, verbatum, that I had one of the engineers working for me find in our library. I elected to use that text so even a layman could grasp the concepts. Sorry you couldnt read it and understand it. Maybe you should read it again a few times till you grasp it, its pretty easy.

Now for some facts. This is a discussion of imbalance and their forces, and how those forces act on mechanical item. It doesnt involve any crap about gyroscopic anything.

In any piece of machinery with a rotating shaft, the raceway of the bearing holding the shaft must deal with the forces generated by an imbalance. That force Skippy is an outward force, plain and simple, and it expressed quite nicely with my formula.

To determine that force, one only needs to know the mass of the imbalance, the velocity its moving at , and the radius. Thats it, you dont have to know jack shit about angular anything to determine that force. The equasion I gave gives you that force. Period, you have nothing more to contribute to that, thats a simple physics fact.

Once you know that force you can determine if it is within the operational design limits of the machine or meets some balance specification established by industrial commitees, or if corrective action is necessary. And yes, it is a centrifugal force, with an equal centripetal force opposed to it. Nothing you say or think will change that fact.

Take your angular acceleration, momentum, and Eulers law and get an education as to when it applies to a discussion or not.

I just love it when schoolkids try to apply things they just dont grasp. By the way, 4 of the engineers working here are getting a world of entertainment value from your posts. I cant make them that happy no matter what I do, thanks for that.

And I dont care one bit if you respect me or not, I have the respect of my peers and customers, and that means much more to me. As for your friend, tell him to mind his own business, and if hes in school with you and agrees with you, tell him to hit the books rather than make smart ass comments. You both need some more education.

As far as this goes, I'm done with it. If you cant grasp it now and want to argue more, take all the posts to your teacher, maybe he can beat some sence into you.

[phatfarm]

Im no physicist, but tires and rims dont fit together like a jigsaw puzzle. Even if they did, by some chance that something doesnt get fitted perfectly, I dont want to risk my life just because some factory says the tires are 100% perfect and another says the rims are 100% perfect. Do you go everywhere buying things that are "claimed" to be perfect? NO.

Didn't you see the commercial where people test things out before they buy them? I certainly would not buy anything where the FINAL product wasn't tested.


PS. You seem smart. You should know that no matter how perfect your manufacturing methods are, some amount of substandard output will get through to the consumer.

[Dan]

...This may be of interest to my new friends here. I am a securities analyst/fund manager for an independant firm out of Salt Lake City. One of my targets a year and a half ago was the tire industry, specifically, how Firestone was fairing after their Ford Exploder debacle. I found that tire manufacturers go out of their way to have tires leave assembly with NO imbalance. Think of it, if something the weight of a tire, with a couple of tons riding on it, spinning at thousands of RPMs the more out of balance, the more likely it will be to fly apart. My point? Why pay the extra $15 per tire to have tires balanced? IF the rims are out of round, balancing won't cure it. Are we just being sheep, thinking that balancing now-a-days is neccessary?

i think you are also forgetting about the sin/cosin of mechancal vibration where it'll peak at one point and go back down and peak again...

[Speedfreak]

If you put the wheel/tire combo on a balancer and it requires weight I guess it needed to be balanced. Newton didn't road test my car. :D

Is the question why should tires need balancing if the wheel is perfect and the tire is perfect? They probably shouldn't.

Remember the thread started talking about tires that explode. Were they perfect tires in an imperfect world?

[OrangeFan]

I have to believe that if you haven't had your wheels balanced you've never driven over 50mph. If you did, you would realize your wheels aren't balanced. Very small imbalances will lead to very wobbly wheels. I'm no engineer or physics professor but I'd say that the wobbliness increases exponentially with speed. Get your wheels balanced. It's $20 a wheel at the most.

[abakos]

Reaper's right about the physics side for sure, it's pretty straight forward stuff if you've seen in before.

I have but only one question: Why is it that almost every wheel/tire combo I've ever seen has required weight after being checked on a balancer? In this perfect world I would expect wheel weights to be a rarity, but almost every wheel on the planet needs them. Sounds like there's a reality check in that lesson somewhere.

No manufacturing process is perfect, I'll guarantee that. I'm a manufacturing engineer, those processes don't exist. They rank up there with frictionless pulleys and perpetual motion. You can get the wheels and tires close, but if it's just a hair off, you'll feel every bit of it when you're at 100+.

If nothing else, even something as simple as using a longer valve stem will throw it off, which has nothing to do with either the wheel OR the tire.