Tire/Wheel Balancing

The technical definition of balance is the uniform distribution of mass about an axis of rotation, where the center of gravity is in the same location as the center of rotation. A balanced tire is one where mass of the tire-when mounted on its wheel and the car's axle-is uniformly distributed around the axle (its center of rotation). Balanced tires can spell the difference between a positive and negative driving experience. Drivers of high performance vehicles will be more sensitive to imbalance problems, but no driver is happy with an annoying vibration.

An out-of-balance tire and wheel assembly:

  • Degrades ride quality and driver comfort.
  • Shortens the life of tires, bearings, shock absorbers, and other suspension components. Vibration is the most noticeable effect of imbalance.
  • It is dependent on vehicle speed.
  • It often first becomes apparent between 40 and 45 mph and increases in magnitude with greater speeds.

Sources of Imbalance
Two sources of imbalance occur in tires: heavy or light spots in the tire and radial or lateral run-out. Imbalance also can be caused by:

  • Variations within the wheel, such as thickness and welds.
  • Rotor and axle imbalances.

Heavy or Light Spot Imbalance
There are two types of imbalance caused by heavy or light spots: static and dynamic.

  • Static imbalance: Occurs when there is a heavy or light spot in the tire so that the tire won't roll evenly and the tire/wheel assembly undergoes an up-and-down movement.
  • Dynamic imbalance: Occurs when there is unequal weight on both sides of the tire/wheel assembly's circumferential centerline. The tire/wheel assembly has a side-to-side

Heavy or Light Spot Balancing
Achieved either statically or dynamically, depending on the type of imbalance that has occurred.

  • Static balance: Achieved with a bubble balancer but does not correct for dynamic imbalance.
  • Dynamic balance: Achieved with a spin balancer where the tire/wheel assembly is balanced both statically and dynamically.

Radial or Lateral Run-out Imbalance
This results from poor bead seating on the rim or the placement of components. Poor bead seating is usually the result of improper mounting or the use of improperly made wheels. A small degree of this imbalance is acceptable, but too great a run-out causes vibration and excessive tire wear.

  • Radial Run-out: An "out-of-round" situation where vibrations are produced as the wheel spindle moves up and down.
  • Lateral Run-out: A side-to-side or wobbling movement of the tire and wheel. It is less common than radial run-out. Sensitivity of a vehicle to vibration from radial run-out is four to eight times that of wobble from lateral run-out.

Run-out Balancing
Depends on whether it is radial or lateral run-out.

  • Radial run-out balancing: Achieved by rotating the wheel and tire assembly two stud positions on the hub, or by rotating the tire 180 on the wheel. If run-out is still over specification, check wheel run-out and mark the low point. Rotate to match the high point of the assembly run-out with the wheel low point. If the assembly run-out is still too high and the wheel is within specification, replace the tire.
  • Lateral run-out: Achieved by using a run-out gauge to check both the tire and wheel. Chalk-mark the highest point of run-out on both the wheel and tire. Replace whichever (wheel, tire, or both) is out of specification.

    1. Wheel is securely seated on the hub face.
    2. All lugs have proper torque.
    3. There is no buildup of dirt between the hub and wheel.
    4. The wheel is not bent.
    5. Both tire beads are securely seated on the rim.

Custom or Alloy Wheels
Custom or alloy wheels require an increased level of care over steel wheels. There are several key points to note when mounting tires.

Avoid scratching or bending alloy wheels during installation.
These wheels are manufactured with extremely soft metals with a greater sensitivity to scratching and distortion under pressure. Modern tire machines apply equal pressure to both top and bottom beads with no pressure on the wheel itself. A pad on the base of the mounting machine protects chrome-plated, painted or machined wheels from scratches and damage.

During the mounting process, proper lubrication
is a must.

Both top and bottom beads must be lubricated with an approved tire lubricant. If the beads do not seat at 40 psi, the installer must break the entire assembly down and re-lubricate the bead areas.

Observe match-mounting procedures.
Proper tire and wheel assembly balancing is important from a vehicle safety standpoint. In high-speed driving, improperly balanced tire/wheel assemblies will cause a vehicle to lose stability and not operate in a safe and comfortable manner. Improperly balanced tire/wheel assemblies also cause abnormal treadwear patterns.

To facilitate proper balancing, Most tire manufacturers place red and yellow marks on the sidewalls of its tires to enable the best possible match-mounting of the tire/wheel assembly. There are two methods of match-mounting tires to wheel assemblies using these red or yellow marks:

  • Uniformity (red mark)
  • Weight (yellow mark)

Improper mounting, underinflation, overloading or tire damage may result in tire failure, which may lead to serious injury. Tire and rim sizes must correspond for proper fit and application. Never exceed 40 psi to seat beads.

Tire changing can be dangerous, and should be done only by trained persons using proper tools and procedures established by the Rubber Manufacturers Association. Failure to comply with proper procedures may result in incorrect positioning of the tire, tube, or wheel assembly, causing the assembly to burst with explosive force sufficient to cause serious physical injury or death. Never mount or use damaged tires, tubes, or wheel assemblies.

Uniformity Method
When performing uniformity match-mounting, the red mark on the tire, indicating the point of maximum radial force variation, should be aligned with the wheel assembly's point of minimum radial run-out, which is generally indicated by a colored dot or a notch somewhere on the wheel assembly (consult manufacturer for details). Radial force variation is the fluctuation in the force that appears in the rotating axis of a tire when a specific load is applied and the tire rotated at a specific speed. It is necessary to minimize radial force variation to ensure trouble-free installation and operation. Not all wheel assemblies indicate the point of minimum radial run-out, rendering uniformity match-mounting sometimes impossible. If the point of minimum radial run-out is not indicated on a wheel assembly, the weight method of match-mounting should be used instead.

Weight Method
When performing weight match-mounting, the yellow mark on the tire, indicating the point of lightest weight, should be aligned with the valve stem on the wheel assembly, which represents the heaviest weight point of the wheel assembly. After match-mounting by either of the above methods, the tire/wheel assembly can be balanced.

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