Industry Terms
[Uniformity] What is Tire Uniformity?
What is Tire Uniformity, or actually NonUniformity?
It is a quantitative measure of force and runout variation within a tire.
The primary parameter measured is Radial Force Variation. Radial Force Variation is a property of a tire that characterizes the dynamic behavior of forces generated (such as steering, traction, braking, and load support) between a vehicle and the road surface. As the tire rotates, the spring elements of the tire make contact with the road surface and are compressed. As each individual spring element rotates out of the contact area it recovers to its original length. Variations in the effective stiffness of each of these spring elements result in radial force variation. The change in effective stiffness and therefore forces generated is due to variation in the thickness of the tire and variation in the elastomeric properties of the tire.
Under the same conditions, if the same load is applied at a constant radius to a rotating tire, it will generate a lateral force and a Lateral Force Variation. As the tire turns, it undergoes repeated deformation and recovery as it enters and exits the contact area. If thelateral force is measured between the tire and the road surface the lateral force will vary as the tire turns. The average value of this generated lateral force is called Lateral Shift. Lateral Force Variation is the small amount of variation in lateral force around the lateral shift. The change in these forces is due to inconsistencies in the tire tread and sidewall area.
Force variation refers to the change in the force as the tire rotates along the surface of the road, providing the center of the tire remains at a constant height above the surface of the road. There must be a load on the tire to generate any force variation.
The Free Radius of a tire is defined as the average radius of the inflated tire from the rotational center of the tire to the tread surface. Tire Runout variation is the variation measured around the free radius. 
[Uniformity] Axis System
To measure tire uniformity, the tire industry uses an axis system which bisects the tire center.
Forces are measured along these axes:

[Uniformity] Force Variations
Force Variation is the change in the forces as the tire rotates. The change in force is due to inconsistencies in tire manufacturing.
The ASTEC^{®} Tire Uniformity Machine measures two types of force variation:
Note: There must be a load on the tire to generate any force variation. Radial and Lateral force variations are measured in both directions of rotation (clockwise and counterclockwise). 

[Uniformity] Radial Force Variation
Radial Force Variation is a property of a tire that characterizes the dynamic behavior of forces generated (such as steering, traction, braking, and load support) between a vehicle and the road surface. As the tire rotates, the spring elements of the tire make contact with the road surface and are compressed. As each individual spring element rotates out of the contact area it recovers to its original length. Variations in the effective stiffness of each of these spring elements result in radial force variation. The change in effective stiffness and therefore forces generated is due to variation in the thickness of the tire and variation in the elastomeric properties of the tire. Once the tire is inflated, loaded, and rotating, the radial force becomes periodic. There is only a slight difference in radial force variation when the tire is rotated in either direction.

[Uniformity] Harmonic Analysis
The measured force variation waveform is called the Composite Waveform.
Fourier analysis expresses the original waveform as the sum of multiple sine waves, or harmonics. Each harmonic is defined by an amplitude and phase angle.
Example: Fourier analysis of the composite waveform, broken into four harmonics. The sum of these four harmonics approximate the original waveform.

[Uniformity] Harmonic Computation
A force variation waveform can be broken down into an infinite number of harmonics. The ASTEC^{®} Computer computes the 1^{st} through the 10^{th} harmonic. Both the harmonic amplitudes and angles are available in the TIGRE™ program for display and recording.
Note: Generally, the 1^{st} and 2^{nd} harmonics of force variation influence the ride quality of a vehicle the most.
[Uniformity] Lateral Force Variation
If a load is applied at a constant radius to a rotating tire, it will generate a lateral force and a Lateral Force Variation. As the tire turns, it undergoes repeated deformation and recovery as it enters and exits the contact area. If the lateral force is measured between the tire and the road surface the lateral force will vary as the tire turns. The average value of this generated lateral force is called Lateral Shift. Lateral Force Variation is the small amount of variation in lateral force around the lateral shift. The change in these forces is due to inconsistencies in the tire tread and sidewall area.

[Uniformity] Lateral Shift
A tire must be rotating to generate a lateral force. As in the radial force diagram, once equilibrium is established for the inflated, loaded, and rotating tire, the lateral force variation becomes periodic.
The average value of this force is called Lateral Shift; the variation is called Lateral Force Variation.
Lateral Shift Variation will change significantly when the direction of rotation is changed. A positive lateral shift in the clockwise direction, (1^{st} DIR.), will become a negative lateral shift in the counterclockwise direction (2^{nd} DIR.). Today tires could wind up in service in either direction of rotation; therefore they must meet the specifications in both directions of travel. 
[Uniformity] Conicity
Conicity is directly related to steering pull. A tire that has high conicity will give a vehicle high steering pull, a strong pull in either direction. The ASTEC^{®} machine will measure the degree, or amount of steering pull.
The word conicity is derived from the word cone. Conicity refers to when a tire physically behaves as if it were shaped like a cone. If a tire has conicity, it would mean that a lateral force is generated in the same direction no matter which way it was rotated.
Conicity is defined as lateral shift clockwise plus lateral shift counterclockwise divided by 2.
Conicity = [(LScw+LSccw) / 2]. The Primary cause is an offcenter belt. 
[Uniformity] Free Radius
The Free Radius of a tire is the average radius of the inflated tire from the center of the tire to the tread surface.

[Uniformity] Loaded Radius
The Loaded Radius is the radius of the
inflated tire under its rated load. A typical loaded radius is an inch and a
quarter less than an unloaded radius.

[Uniformity] Radial Runout
Radius between tire center and road (or Loadwheel) when loaded.

[Uniformity] Lateral Runout
Variation in sidewall geometry while inflated, loaded and rotating. 
[Uniformity] Bulge / Depression
During tire building, things can happen that affect the outside appearance of the finished sidewall of the tire. During the tire manufacturing process an overlap, or gap, in the cord material will show up in the finished tire as Bulges or Depressions. Bulges and depressions are appearance problems, which may become serious enough to prevent the tire from being sold. 
[Balance] Imbalance Cause and Effect
All tires and wheels have some measurable imbalance, typically caused by inaccuracies in tire components, construction, and curing; and inaccuracies in wheel manufacturing. Imbalanced tires and wheels cause the following ride disturbances:
 vertical forces
 foreaft forces
 steering moments
 camber moments
[Balance] Principles of Imbalance Forces and Moments  Centrifugal Force
Centrifugal Force

[Balance] Principles of Imbalance Forces and Moments  Measurement System
Measurement System

[Balance] Types of Imbalance  Static
Static Imbalance This Figure illustrates the static imbalance concentrated mass at the TWA centerline. The centrifugal forces are shown as continuous waveforms, which will be analyzed to determine mr. 
[Balance] Types of Imbalance  Couple
Couple Imbalance This illustration shows a TWA with two mass concentrations, equal and opposite in direction, and on opposite sides of the TWA centerline.

[Balance] Types of Imbalance  Dynamic
Dynamic Imbalance Dynamic imbalance is the combination of static and couple imbalance. Dynamic imbalance is simulated using weights positioned in typical static and couple scenarios. As a vehicle travels at a high rate of speed, the passengers may experience a combined bouncing and wobbling sensation. 
[Balance] Imbalance Correction
Vehicle manufacturers and tire retailers compensate for imbalance by adding weights to the tire and wheel assembly. A simplified example of an imbalance correction is illustrated. Weights are applied in matching locations on the top and bottom plane, thus correcting any imbalance and eliminating ride disturbance.
[Balance] Units of Measure for Correction  Static Imbalance (or Unbalance!) Units
Static Imbalance (or Unbalance!) Units
Scientific Units:
 cgs: gram centimeter (g•cm)
 SAE, AIAG: kilogram millimeter (kg•mm)
 English: ounce inch (oz•in)
Auto Industry Units:
 Grams (or Ounces) at the correction radius
The ‘Static Scientific Units’ are very commonly used for wheel specs.
Example: 8 oz•in static imbalance, If r = 8 in The imbalance would be expressed as “1 oz imbalance” applied at 8 in, and divided in half on each side of wheel.
[Balance] Units of Measure for Correction  Couple Imbalance (or Unbalance!) Units
Couple Imbalance (or Unbalance!) Units
Scientific Units:
 cgs: gram centimeter²(g•cm ²)
 SAE, AIAG: kilogram millimeter²(kg•mm²)
 English: ounce inch²(oz•in²)
Auto Industry Units:
 Grams (or Ounces) at the correction radius in the correction plane37
Example: 56 oz•in² couple imbalance If r = 8 in and w = 7 in The imbalance would be expressed as “2 oz imbalance” applied at correction radius, in the correction plane, with one half the weight (1 oz) in each plane.
[Balance] Units of Measure for Correction  PerPlane or Dynamic Imbalance Units
PerPlane or Dynamic Imbalance Units
Scientific Units:
 cgs: gram centimeter (g•cm) in the correction plane
 SAE, AIAG: kilogram millimeter (kg•mm) in the correction plane
 English: ounce inch (oz•in) in the correction plane
Auto Industry Units:
 Grams (or Ounces) at the correction radius in the correction plane
The ‘PerPlane Scientific Units’are very commonly used for tire specs.
[Balance] Knockon Weights
Wheel with two standard knockonWeights
[Balance] Adhesive & Knockon Weights
Flangeless Wheel with One Adhesive Weight and One Standard Knockon Weight.