# Tire Uniformity Vibration and Sounds

Tire uniformity refers to uniformity of weight, dimensions and rigidity.
However, since uniformity of weight is ordinarily called “wheel balance” and uniformity of dimensions is called “run-out” uniformity alone usually refers to “uniformity of rigidity”.
When a tire receives a load, it flexes, acting almost as if it were a spring.
The tread, rubber, carcass, belt, and other materials of which the tire is composed are not uniformly distributed around the circumference of the tire, so tire rigidity is not uniform.
As a result, the tire is subject to subtle fluctuations in the way it flexes as it rotates.
These fluctuations introduce a periodic variation in the force which it receives from the road surface.
This force can be resolved into three components:
Fluctuation in the vertical force acting upwards toward the tire’s center (parallel to the tire’s radius).
Lateral Force Variation (LFV)
Fluctuation in the horizontal force acting parallel to the tire’s axis.
Tractive Force Variation (TFV)
Fluctuation in the horizontal force acting parallel to the tire’s direction of motion.

Among RFV, LFV, and TFV, the most important is RFV.
On an actual vehicle, a tire with a high RFV imposes a vertical vibration on the axle, which can lead to excessive vibration during high-speed travel. Two ways to reduce RFV are (1) to trim minute quantities of rubber from the tire circumference and (2) to shift the tire so that the point with the maximum RFV lines up with the point on the wheel rim having the minimum radial run-out.
This is known as “phase matching”.