Wheels that are not balanced or are out of balance generally produce a vibration that is uncomfortable to drive in and results in premature wearing of suspension and steering components, rotating parts and tyres.
Correctly balanced wheels help to eliminate vibration and avoid premature wear caused by an imbalance in the rotating wheel and tyre assembly.
The first sign that your wheels may be out of balance is when your steering wheel starts to wobble above a certain speed. The lightweight of modern cars means that they don't dampen down the vibrations caused by spinning wheels in the way that older, heavier vehicles could.
A driver may not always sense an imbalance at the steering wheel. It could be present with but dampened by the vehicle weight. This is why balancing is equally important for both front and rear wheels.
Once the wheels have been removed from the car and new tyres have been fitted, the wheels are the placed on a balancing machine one by one. The machine then spins the wheel to find and locate where additional weights may be needed in order to make sure the wheel is the same weight all the way around. These weight differences are very minimal but can be noticed if additional weights are not added.
Steel wheels use clip on weights that are tapped on to the rim where the tyre meets the edge. Additional weights are replaced every time new tyre is fitted as the overall balance can change over time.
Alloy wheels use adhesive weights that are stuck to the inside of the alloy. Adhesive weights are used because clip on weights damage alloy rims and allow for dirt, water and excess oil to seep into the tyre and cause corrosion. The tyre is likely to also deflate much quicker if a clip on weight is used.