a good design allows for a simple adaptation to make a dual purpose able item, like a truck/trailer towing, or a sofa sleeper, or a draftsmans table, or this tractor / train engine

in the above, visible on the far side rear rim, they bolted on a flange

and that made this tractor able to roll on rails as the front rims were made with flanges and the right distance apart

http://1914-1918.invisionzone.com/forums/topic/173218-ww1-military-motors-1916-set-x-50-cards/?page=93

if the tractor looks a little familiar, maybe you're remembering the trench crosser http://justacarguy.blogspot.com/2016/01/the-english-wheel-tank-trench-crosser.html