You may have noticed that every time, if you have been to a reputable tyre retailer, a wheel is removed for say a replacement or to have a repair made to a tyre, that the technician when they have fitted and inflated the tyre that he then bolts the wheel to a machine and then it spins like crazy?
What’s all that about you may have asked yourself? You may have asked the technician, and he may have replied “balancing mate”?
Here is a long winded but thorough explanation of how a balancing machine works taken from Wikipedia:
“When the wheel and tyre is spun and the assembly commences to wobble about the self-aligning bearing, the restraining springs attached to the second bearing absorb the out of balance forces and the deflection of the mainshaft and spindle.
An electro-magnetic moving coil vibration detector (transducer) is installed vertically between the second bearing and the machine frame. When the wheel assembly wobbles, the armature (rod) in the centre of the transducer coil moves in and out of a strong magnetic field provided by the permanent magnet. This causes the armature coil to generate a voltage proportional to the relative movement of the rod. The output signal from the detector is a direct measure of the imbalance of the wheel assembly. It is therefore fed into a compensating network which converts the signals into the required balance weight to be attached to the outside of the wheel rim in the left hand plane. These modified, but still very weak, electrical signals are then passed through a filter which eliminates unwanted side interference. They are then amplified so that they can activate the stroboscope device and the weight indicator meter.
The weight indicator meter computes the voltage amplitude signal coming from the detector and, when calibrated, indicates the size of the weight to be added to the plane of balance, in this case the outside of the wheel. Conversely, the stroboscope determines the angular phase of the balance weight on the wheel. This is achieved by the sinusoidal voltage being converted into a sharply defined bright flash of light in the stroboscope lamp. A rotating numbered transparent drum is illuminated by the stroboscope flash and the number which appears on the top of the drum relates to the phase position of the required balance weight.”
In short though, if your car develops a wobble through the steering wheel, generally at around 50 to 60 mph, then this is probably the effect of an imbalanced wheel or two. Run your car into us or another reputable garage and we will check your wheels. First we will do a test spin, leaving all the current balance weights in place to determine if there is a problem. The technician will also check to see if there is a problem with the tyre, any bulges or signs of the tyre going out of shape (this can happen if the tyre ages or has had a severe impact). Then we will remove the old balance weights and re-spin bringing up a number on the display. This number denotes the amount of imbalance on both the inside and outside edge of the wheel in grams. We will then place the weights where the machine indicates (this is basically counter balancing the heavy points of the wheel and tyre combination). Then the wheel will be spun again and hopefully the display will show zero.
We use Hofmann wheel balancers, not the fancy ones with the full colour TV displays, but high quality, accurate and easy to use machines! We always have done, right from the start. We trust them to do a decent job. it’s a very important, integral piece of what we do. An imbalanced wheel is not only very annoying but causes extra stress on other vehicle components, bearings, bushes and ball joints.
I hope this has explained balancing in a scientific and then in my own inimitable style.