When this happens, the wheels in front pull the trailing wheels
into rocks; the wheels behind push the leading wheels into rocks.
In efforts to improve their riding characteristics, the swing link bogies had to be replaced with ones of sliding design and the trailing wheels
had to be modified with outside rather than inside bearings.
The driving wheels were placed near the front end of the frame and two trailing wheels
were added to keep the machine in balance.
That means it has four wheels in its leading pilot truck, which helps guide the locomotive into curves, followed by two sets of six driving wheels, and four trailing wheels
that support the rear of the engine and its massive firebox.