If the tire is not checked, it has the potential to cause vibration in the suspension of the vehicle on which it is mounted. 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). In the tire factory, the tire and wheel are mounted on a balancing machine test wheel, the assembly is rotated at 100 RPM (10 to 15 mph with recent high sensitivity sensors) or higher, 300 RPM (55 to 60 mph with typical low sensitivity sensors), and forces of unbalance are measured by sensors. While some very small shops that lack specialized machines still do this process, they have been largely replaced in larger shops with machines.ĭynamic balance requires that a principal axis of the tire's moment of inertia be aligned with the axis about which the tire rotates, usually the axle on which it is mounted. In tire retail shops, static balancers are usually non-rotating bubble balancers, where the magnitude and angle of the unbalance is indicated by the center bubble in an oil-filled glass sighting gauge. In tire manufacturing factories, static balancers use sensors mounted to the spindle assembly. The amount of deflection indicates the magnitude of the unbalance, and the orientation of the deflection indicates the angular location of the unbalance. If the center of mass of the tire is not located on this vertical axis, then gravity will cause the axis to deflect. Static balance can be measured by a static balancing machine where the tire is placed on a vertical, non-rotating spindle. Static balance requires the wheel center of mass to be located on its axis of rotation, usually at the center of the axle on which it is mounted. Tire balancing is distinct from wheel alignment. Tires may be rebalanced if driver perceives excessive vibration. When tires are fitted to wheels at the point of sale, they are measured again on a balancing machine, and correction weights are applied to counteract their combined unbalance. Tires with large unbalances are downgraded or rejected. Tire balance is measured in factories and repair shops by two methods: with static balancers and with dynamic balancers. The frequency and magnitude of this ride disturbance usually increases with speed, and vehicle suspensions may become excited when the rotating frequency of the wheel equals the resonant frequency of the suspension. When the wheel rotates, asymmetries in its mass distribution may cause it to apply periodic forces and torques to the axle, which can cause ride disturbances, usually as vertical and lateral vibrations, and this may also cause the steering wheel to oscillate.
Tire balance, also called tire unbalance or tire imbalance, describes the distribution of mass within an automobile tire or the entire wheel (including the rim) on which it is mounted.
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