Maybe Ed was responsible for carrying the other tires needed to switch it back to 'standard' road use when the snows melted? If every vehicle carried one tire then the 5th could be used for road work or similar.
Great lookin' vehicle now someone tell me why the ferk has it gotta spare wheel on t'back?
My guess and its been touched on by others is that the kit is (a) based on a prototype, a conversion from a standard wheeled armoured car and (b) much like the aerosans the wheels could be put back on for summer use etc. Aerosans came with wheels so they wouldn't become stranded when the snows melted.
It looks like a very simple conversion from wheels to a ski version. On saying that the chassis doesn't look typical BA-64?
Anyhoo; I want one for the tracks and ski's. They'd look cool on my 'what if' winterised Land Rover WMIK