Imbalance is an uneven distribution of mass about the tyre/wheel centre-line. Balancing is an essential process when fitting new tyres to wheels or after the tyre has been removed and then refitted to the rim. Most standard production tyres and wheels will, when built, have slight imbalances in their construction due to the nature of the manufacturing process. Balancing allows the technician to determine where these “heavy” spots are located and counteract the effect with balance weights.
An imbalance in a tyre/wheel assembly can usually be noticed as one of two things. Firstly an imbalanced front wheel will give a vibration that can be felt through the vehicle steering wheel. Secondly, an imbalance in the rear wheels will result in a vibration that can be “felt” through the vehicle body. As well as being uncomfortable this imbalance can have a detrimental effect on the vehicle’s handling and may also cause slightly increased fuel consumption due the constant change in wheel speed.
Wheel balancers will check two kinds of balance, “static” (A) and “dynamic” (B). Static imbalance causes a wheel to shake up and down as it spins, so static balance is achieved when both halves of the tyre wheel assembly weigh exactly the same. Dynamic imbalance causes a tyre and wheel to shake back and forth or sideways as it spins. Dynamic balance is achieved when the inner and outer sides of the wheel and tyre weigh the same.