Just pondering the question while taking a train and a plane the other day. I assume the train's wheels are machined perfectly to begin with, and without tires, there wouldn't be significant variation throughout the wheel's life. Not sure about alignment. And on planes, the time rolling on the ground is minuscule over the tire's lifetime, although when it does roll it can be over 100 mph so imbalance would magnified. If they do get balanced, is the equipment and weights similar to automotive?