[ben11kehoe]

They keep the train centered by the differential effect. The angle of the cone is very slight, nowhere near enough for gravity to overcome friction to cause the train to slip laterally into the center. And then keeping the train centered as the track turns results in the train turning with the track.

[GhostVII]

Sure, but I guess I'm wondering if that is just a convenient effect of the centering, or if it is actually necessary to prevent the wheels from skipping.