"with the exception that most spinning things have a critical speed ( whole nother animal that is )." Quote
All spinning things have a critical speed to one extent or another. What happens at a critical speed - it vibrates/ shakes. Vibration node points How this applies to tires is what if a vibration node point occurs at a speed at which we like to cruise, say 75mph. With dynamic balancing we can minimize these critical speeds (vibration node points) and move them out of our operating speed range.