Wheel Balance

Wheel balance is the state in which a tire and wheel spin with all their weight distributed equally. This can apply to both static and dynamic balance.

A wheel should be well balance for running on different road conditions to undergoing cornering forces. Before "assembly of wheel" a wheel should perform static and dynamic balance test. 

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. [1]

An imbalance in a tyre/wheel assembly can usually be noticed as one of two things. Imbalance is an uneven distribution of mass about the tyre/wheel center-line. 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 vehicles handling and the wear of tyre thread, suspension linkage and shock absorbers. [1]

Physics of Tyre imbalance [2]

Wheel balancers will check two kinds of balance, “static” and “dynamic”. Static imbalance causes a wheel to shake up and down (wheel hop) 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 (wheel shimming). Dynamic balance is achieved when the inner and outer sides of the wheel and tyre weigh the same. [1]

Wheel spots [1]

Dynamic unbalance causes the wheel assembly to turn inwards and then outwards, with each half revolution. As speed rises, rapid side movement of the front wheels causes a sideways-vibration, or wheel wobble effect, at the front of the vehicle. [1]

Feature Link: "Wheel Balancing"

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References:

[1] Trade of Motor Mechanic: Module 7: Unit 1: “Wheels & Tyres” by SOLAS, In cooperation with: Subject Matter Experts; Martin McMahon & CDX Global Curriculum Revision 2.2 16-01-07 © SOLAS 2013.

[2] Figure: "static & dynamic imbalance": https://en.wikipedia.org/wiki/Tire_balance#Static_balance