John Gray's 'mixed' frame had an inside frame for the cylinders and driving wheels, with inside bearings, and an outside frame for the 4ft-diameter (1.22m) leading and trailing wheels
, using outside bearings.
When this happens, the wheels in front pull the trailing wheels
into rocks; the wheels behind push the leading wheels into rocks."
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.
The railroad maintains a steam locomotive of wheel arrangement 2-8-0 (two pilot wheels in front, eight drive wheels, no trailing wheels
under the firebox), known in the trade as a consolidation type.