One of the reasons tire shaving, static balancing, and dynamic balancing don’t really work is because of the actual dynamic forces working on any ONE tire, compounded by a factor of 4.
Its a difficult lesson to absorb, but let’s try:
We have two unbalancing forces in every moving tire (not counting weight differences); Radial Force Variation and Momentary Vector Static Friction.
RFV covers all the inconsistencies in a tire, from different stiffness points in the sidewall to soft spots in the tread area itself. Consider the tire to be made up of several thousand springs, arranged in a circle, around the wheel hub. As it rolls down the road, with weight on it, any variation on those springs will cause the tire to “hop” each time a stiffer spring is encountered.
On a standard “spin balance” machine like most tire shops have, this is not encountered, since the wheel is roating in free air space, with no load attached, and a load is where it gets interesting.
In the picture above, imagine 4 points on the tire: A) where the tire touches the roadway, B) the top of the tire directly ABOVE point A; C) and D) at the sides of the tire at axle height (midway between A and B.
If the tire is propelling the car along, to your right, at 50 mph, what is the speed of the tire at point A? ANSWER: it is at a momentary dead stop, 0 mph, as it gains friction with the road surface. As soon as the tire rotates 1/4 turn, the rubber at point A will be at point C. How fast is the tire going at point C? 50 mph. At the top of the tire, at point B, how fast is the tire moving? 100 mph. And then once again down to 50 at point D. This speed variance causes what is known as a standing wave, where the tires is always trying to catch up to itself:
In short, balancing a tire, for all speeds and loads, cannot be done. Having said that, the tire companies and their balancing equipment to a fantastic job of coming real close!