When an automobile draiver steps on the accelerator, the nose of the car moves upward. When the driver brakes, the nose moves download.
You can change the accelaration of the car and see how the force were distributed between tires.
You can also drag those vectors(up/down) to change the weight of the car or the weight of the loads.
You also can drag the tire(left/right) to change the position of the tire and see how the loading were redistributed.