What it Does:
Tire Balancing corrects the imbalance of a rim and tire assembly. Imbalance refers to the condition caused by uneven rotational force caused by heavier and lighter spots within the rim and tire assembly (say for example, a small section of the tire that is 1 oz lighter than the rest), and it may also help compensate for minor uneven rotational forces caused by the rim and tire not spinning in a perfectly true circle.
Why This Matters:
Think of a baseball: It only weighs about 5 ounces. But when a major league pitcher throws it at 85-90 mph, it carries a lot of force. Tire balancing is a similar concept. We commonly see tire and rim assemblies out of balance by anywhere from .25 to 3.5 ounces. The uneven forces resulting from this additional (or lacking) weight being spun at the tire’s rotational speed can impact your vehicle’s ride quality. Nearby suspension and steering components also “feel” these uneven forces, and usable lifespan of nearby suspension and steering joints can be affected by the constant vibration that they’re exposed to. (This doesn’t mean that they’ll always fail quickly, but please consider the concept of a suspension joint that *could* have lasted 150k miles, but it wears out at 110k miles instead.) While this is a very long time, this would still impact your long-term service costs for your vehicle.
Possible Problems and Concerns
Imbalance
Normal:
Except for rare occasions, even high quality tires and rims, in good condition, will need a small amount of weight added to correct for imbalance. This imbalance is caused by excess weight or lack of weight due to differences in rotational mass (for example, more dense versus less dense sections of the tire.) This sort of imbalance is to be expected and should always be addressed when tires are replaced.
Severe:
Lower quality tires or a defective rim (while still, may not visible to the naked eye) may result in an abnormally high amount of balance weights being required. While addition of weights will help with ride quality, this may not be sufficient to achieve a fully smooth ride.
Abnormal:
Bent rims and tires with structural failure will result in imbalance that cannot be fully corrected with addition or removal of weights.These concerns may come with other concerns too (a tire with structural failure is unsafe, and a severely bent rim can result in abnormal tire wear etc.)
Equipment
Most balancing is done with the rim mounted on a centering cone on the balancer. However, some rims will not properly or reliably center in this fashion and require the use of adapters for lug hole centering. An improperly mounted rim will yield incorrect imbalance readings, resulting in the tire not being balanced correctly.
Lack of Check-Spins
Due to mounting tolerances and limitations of machine logic, the first balance procedure is not always successful. This is especially true if the balance is being adjusted to a fine degree. After the first balancing stage, the rim should be “clocked” in a differential rotation position on the centering cone, and imbalance readings checked again. It’s ideal to get the imbalance down below .25oz or so.
Poor Surface Preparation
Many rims use adhesive weights, and those weights spin at the speed of the tire! If they are bonded to a dirty surface, they are more likely to fly off while the vehicle is in motion.
Effects on Other Components
Tire and rim imbalance causes excessive vibration while the vehicle is moving. In addition to impacting ride quality, this imbalance can encourage things like improper tire wear, decreased longevity and performance of suspension components, and possibly even reduced bulb life! You can think of this somewhat like “torture/vibration testing.” If you shake things around too much, they don’t tend to last as long. Such affects (other than ride quality) will not be immediate, but they can impact your overall service costs over years of vehicle ownership. Please note as well that vehicles are designed to insulate vibration from the cabin. Just because you don’t feel it yourself doesn’t mean that it’s not happening outside the cabin. (You are more likely to feel a severe imbalance though.)
General
Tires should always have their balance checked after the first installation, and it is common to see imbalance develop again as the vehicle accumulates mileage and the tires wear accordingly.