It’s all a Balancing Act!
It’s the age of fully automated wheel balancing with sophisticated electronic wheel balancers. So why do we still have the arguments of Static vs Dynamic Wheel Balancing?. After all the process of wheel balancing is what most would class as Wheel Balancing 101 right? Surely with all this technology, wheels and tyres are balanced perfectly?
Well actually 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 indeed have an issue or require calibration, you would be surprised how often it comes down to operator error. Which is disconcerting due to the number of wheels they have worked on previously.
I could go into intricate details behind the science of wheel balancing. But let’s be honest you’re not interested in sitting in a City & Guilds lecture, If you were you would have already done it.
So I will try to cover the main issues that we often have to explain and make it as plain as possible
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 Balancing!!! Unless you are balancing a vintage car with very narrow wheels, you SHOULD NOT !!! be using the static balance setting. People will often use this parameter to make balancing easier or merely to save weights. Static balancing uses one set of wheel weights in the centre of a wheel whereas, Dynamic balancing uses two sets of weights. See the cross-section below for example.
You may be able to get the display on a wheel balancer to show zero on its imbalance reading. But this does not mean the wheel is balanced correctly, far from it! I will try to explain this concept in a manner that is as easy to understand as possible. Note:- If the simplicity of the following article annoys you then tough! Please refrain from becoming a keyboard warrior.
Static wheel balancing technically refers to a wheel that’s centre of gravity is balanced around its axis of rotation. It means that if you were to place the wheel on a free rotating axle, it would remain stationary regardless of its position. If a wheel is statically imbalanced, then the heavy spot will fall to the bottom. By placing the matching weight on the opposite side of the heavy spot, the imbalance can be dialled out.
This method has used to balance narrow vintage car wheels for many years. Most owners of motorcycles with narrow wheels still used this method of wheel balancing. So do many car garages that deal specifically with vintage cars. This type of balancing is easy to do and can be done by most competent people. It also requires simple tools to carry out and can be done at home.
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. 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 program. The wider the wheel and tyre gets, the more important this becomes. When balancing a wheel dynamically, you are counteracting rotational forces, both on a vertical plane and a lateral plane. Now there are more forces than this acting on a rotating wheel and tyre, but again we’re keeping it simple. Vertical or Static imbalance on a wheel that is rotating will cause the wheel to spin elliptically. This is due to the imbalance weight that is wanting to fly away from its centre. This causes the wheel to bounce up and down. In turn, can create vibration and rumbling sounds within the car. It will also cause the tyre to wear badly. Imagine holding a bicycle wheel in your hands, and on the wheel, you tape a heavy weight to it. Now if you get someone to spin that wheel you will feel it move up and down. I’m sure you had done this when you were younger The dynamic imbalance is when you have a heavy spot that is off centre to the midline when viewing from above.
Now without getting into a physics lesson, centrifugal and centripetal forces are at play here. (technical people calm down I know you want to shout, but we’re trying to keep it simple) This off-balance spot will pull the wheel off axis when rotating. Think of it like this. 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. Now while the load 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. Now when applied to a wheel, this causes a side to side motion as it rotates around an axis. Creating “shimmer” which is more noticeable on a flexible axle such as a steering joint. This shimmering causes the weight to pull on the steering rack causing steering wheel vibrations. On rigid axles such as the rear of a car, the shimmer will cause tyres to wear with a fluttering effect. And create a noticeable vibration within the vehicle, especially at higher speeds. To counteract this force, place a weight of equal amount opposite the off-centred imbalance.
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, you can now see why all “modern” wheels should be dynamically balanced. And by implementing this method into your business (if you are not already doing so), 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 “Contact Us” where we can talk about any requirements for your business. Again I must state that this is a simple description of Static and Dynamic balancing. And I am sure there will be the purists out there that are spitting feathers over this article. As well as engineers wishing to throw large heavy objects in my general direction. Sorry but as stated earlier, this post was not intended for you.