A Question about how Emily drives.

My guess is because of the larger circumference of the wheel. The traction tires keep it rolling and not sliding while being "pushed" by the tender. Plus it would make her free wheel better.

I wish Stephen had traction tires, too... Maybe a modification is in order?
Oh wait, nevermind. I mean, he probably should on the Plarail version, but only seconds after posting this I remember that TrackMaster Stephen is self-powered, and has traction tires on his back wheels.