A Question about how Emily drives.

As of late I've been having something really eat away at me for quite a while, and I don't know why I'm so curious, but I'd like to get it out of my brain for good. I've been wondering just how TrackMaster and Plarail Emily is driven. I've seen her larger wheels with the siderods connected to them with traction tires, but I know her tender can be disconnected, and as far as I'm aware, she isn't self-powered. So, if she's tender-driven, why exactly even have traction tires on the engine itself? It's not done with Hank, Harvey, Molly, and Murdoch.

P.S.: Is it just me or does TrackMaster Charlie seem to be shorter in length than an average TrackMaster engine like Thomas?