I'm thinking that you want them to go flat. When they're fresh off the factory floor we can think of them as perfect spheres. So while riding one ball touches t

I'm thinking that you want them to go flat. When they're fresh off the factory floor we can think of them as perfect spheres. So while riding one ball touches the ground at its maximum radius, then it falls off a bit, then rises to the maximum radius of the next ball etc, so the rider keeps going up and down a bit. Once they become a bit flat the 4 sides will squash down into a cube type shape, also equalizing with its neighbors so that the overall shape becomes flat and the ride becomes a lot smoother.