Wheel Balancer Wiki
Static balance can be measured by a static balancing machine where the tire is placed in its vertical axis on a non-rotating spindle tool. The spot on the tire with the greatest mass is acted upon by gravity to deflect the tooling downward. The amount of deflection indicates the magnitude of the unbalance. The angle of the deflection indicates the angular location of the unbalance. In tire manufacturing factories, static balancers operate by use of sensors mounted to the spindle assembly. In tire retail shops, static balancers are usually non-rotating bubble balancers, where the magnitude and angle of the unbalance is observed by looking at the center bubble in an oil-filled glass sighting gauge. While some very small shops which lack specialized machines still do this process, they have been largely replaced in larger shops with machines.
Dynamic balance describes the forces generated by asymmetric mass distribution when the tire is rotated, usually at a high speed. In the tire factory, the tire and wheel are mounted on a balancing machine test wheel, the assembly is accelerated up to a speed of 300 RPM or higher, and sensors measure the forces of unbalance as the tire rotates. These forces are resolved into static and couple values for the inner and outer planes of the wheel, and compared to the unbalance tolerance (the maximum allowable manufacturing limits). If the tire is not checked, it has the potential to wobble and perform poorly. In tire retail shops, tire/wheel assemblies are checked on a spin-balancer, which determines the amount and angle of unbalance. Balance weights are then fitted to the outer and inner flanges of the wheel. Dynamic balance is better (it is more comprehensive) than static balance alone, because both couple and static forces are measured and corrected.
The physics of dynamic balance
Road force balancing
Road Force Balancing takes the tire & wheel assembly and optimizes wheel run out and weight loaded tire deflection. After the road force value is minimized the wheel & tire assembly is balanced. Road force balancing has been in use at the original equipment level for many years but has only appeared in the replacement market since approximately the late 1990s.
Vibration in cars and light trucks occurs for many reasons. Common reasons are poor wheel balance, imperfect tire or wheel shape, brake pulsation, and worn or loose driveline, suspension, or steering components. Occasionally and rarely, one will find foreign material stuck in tire's tread causing vibration e.g. road tar in summer.
Every year, millions of small weights are attached to tires by automotive technicians while balancing them. According to the US Environmental Protection Agency, worldwide these total more than 20,000 tonnes of lead annually.Traditionally, these weights have been made of lead, but since lead is a toxic metal, political authorities and industrial groups are in the process of converting to materials that are less toxic than lead.The tire weight shown in the illustration has a "Zn" stamp, indicating it is made of zinc rather than lead.