It’s all a Balancing Act!
Here we are in the age of fully automated wheel balancing carried out using sophisticated electronic wheel balancers. So why do the arguments of Static vs Dynamic Wheel Balancing still linger on like a bad smell?
After all the process of wheel balancing is what most of us would class as Wheel Balancing 101 right? Surely with all this technology, wheels and tyres are balanced perfectly?
Well in most cases no they are not. And what gives me the confidence to say that? …. Experience!
As an engineer, I often attend to sites with reports of a faulty wheel balancer. The general complaint is “… the machine needs calibrating”, and this diagnosis usually derived from frequent customer “comebacks” or that operatives are repeatedly “chasing weights.”
And although on some occasions the wheel balancer does actually have an issue or requires calibration, you would be surprised how often the issues come down to operator error. Which is bit disconcerting to think about considering the number of wheels they have most likely worked on previously.
Now I could go into the intricate details behind wheel balancing, but let’s be honest you’re not interested in sitting in a City & Guilds lecture are you. If you were then I would have thought you would have done so already, and you wouldn’t be here reading through my waffle.
So, with that in mind I will try to cover the main issues that we often have to explain to tyre fitters, and where possible I will make it as plain as possible to make life simple.
Static vs Dynamic Wheel Balancing
Ok so before we deal with the physical aspect of wheel balancing let us first address a significant issue of Static wheel Balancing!!!
Unless you are balancing wheels from a vintage car with very narrow wheels, you SHOULD NOT !!! be using the static balance setting.
Tyre fitters will often use the static wheel balancing parameter because they believe it makes the process easier and quicker.Worse yet some businesses will use static wheel balancing to save on the amount weights being used in an attempt to improve profits.
Static wheel balancing is carried out using one set of wheel weights mounted in the centre of a wheel. Dynamic balancing on the other hand uses two sets of weights. See the cross-section below for an example.
Now admittedly when balancing a wheel using the static wheel balance parameter, you may well be able to get the display on a wheel balancer to show zero on its imbalance readings, …… after all you have just balanced the wheel in a Static fashion
BUT !! this does not mean the wheel has been balanced correctly, in terms of modern day vehicles, it’s far from it!
And this is the reason for writing up this article, a very simple quick reference guide to hopefully explain the static vs dynamic wheel balancing concept in a manner that is as easy to understand as possible.
So, if the simplicity of the following article annoys you then tough! …. It has been written in this manner for a reason, please refrain from becoming a keyboard warrior and sending emails pointing out some random technicality.
Static balancing refers to the balance point of an object around its axis of rotation.
What this means is that if you were to mount the any object on a free rotating axle, then it would remain stationary regardless of its position it was left in.
If an object has a static imbalance then when mounted to a rotating axis, the heavy spot of the wheel will want to fall to the bottom. (As detailed in the image below)
By placing the matching weight on the opposite side of the heavy spot, the imbalance can be dialled out.
This very principal has led to the method developed and used to balance motorcycle rims and narrow vintage car wheels for many years. You will find some owners of motorcycles with standard width wheel rims still use this method of wheel balancing, as do many car garages that deal with vintage cars.
The wheels are mounted onto a shaft which then freely rotates between two bearings. Any heavy spot will rotate and settle at the bottom of the frame, you would then apply a small amount of weight directly opposite i.e… at the top. You would then rotate the wheel a bit and let go, then “Rinse & Repeat” the previous process until the wheel no longer moves when you let it go.
The tools are cheap and readily available, lightweight and portable. You could even balance your wheels on the kitchen table, although your significant other may not approve!
Now, this is where things change and we need to fall down the proverbial rabbit hole a bit….
In order to explain Dynamic Imbalance, we need to examine part of Newton’s first law of motion …… “an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force”.
People stay with me here, it will make sense i assure you !!!!
Now without getting into a physics lesson (and as a pre-empt …. any technical people still preasent, please take a chill pill and calm down for a moment I know you want to shout, but we’re trying to keep it simple) what this means is as follows
Take a piece of cord, string or fishing line and attach a weight to one end. Now start to spin that weight around your hand in a continual fashion. You will see the weight turning around a central point, specifically around the point of which the force is applied i.e., it spins around your hand
Now if you let go of the string you would see newtons law come into play and the weight would fly off (in the direction it was traveling in, at the point in which you let go) I’m sure you have all done and experienced this as a kid.
But rather than letting go if you were to hold onto the string and allow the weight to freely rotate instead, then the Centripetal force or centrifugal force (depending on your point of reference) will act on it and you will feel the weight pulling your arm towards the weight (making your hand move and down) this is the static Imbalance.
Now if you are still here, then big kudos to you for wanting to learn something new (it says a lot about your character) but i am going to guess that you are now asking “what about the Dynamic Imbalance?”
So, lets repeat the process above but this time while the load (or weight) is rotating suddenly move your hand a few inches towards or away from you. You will see the weight move from its original course to a new position where it is again rotating around the axis of applied force or point of rotation.
Now when this effect is applied to a wheel, this causes the force of the point of axis imbalance to create a “side to side” motion as it moves around to meet the point of rotation and this creates a “shimmer”
This “shimmering” causes the imbalance to pull on the steering rack which induces a vibration that is particularly noticeable on a flexible axle such as a steering joint, especially at higher speeds. On a rigid axle such as the ones found at the rear of a car, the shimmer will cause tyres to wear with a fluttering effect, prematurely ending the life of the tyre and also creating a noticeable vibration within the vehicle
To counteract this force, you need place a weight of equal amount opposite the off-centred imbalance.
If you are balancing any modern wheels (and by modern, I refer to wheels wider than 4 Inch), you should always use a Dynamic weight balancing program. And to be blunt the wider the wheel and tyre gets, the more important this point becomes.
Wheel Balancing 101
So, there you have it, a fundamental break down of the differences between Static and Dynamic Wheel Balancing.
The proverbial homage to wheel balancing 101 as it were.
Hopefully now you can see why all “modern” wheels should be dynamically balanced. And by implementing this method into your business (if you are not doing so already), you will be providing your customers with a superior service.
If you have any questions regarding this subject, or indeed would like to discuss staff training. Please click the contact button below where we can talk about any requirements for your business.Contact Us
Again, I must state that this is a simple description of Static and Dynamic balancing.
I am sure there will be the purists out there that are spitting feathers over this article for not being scientifically or technically accurate, and no doubt there will be engineers wishing to throw large heavy objects in my general direction for being so laymen. But as stated earlier this post was not intended for you and I bear no apologies for this.
Hope this helps