Cripes, you are right! In every case but one it is a twin wheel with totally mismatched tyres. In the other case it is a single front wheel.
Looking at "Royal Flying Corps Instruction dealing with the use, maintenance, repair and inspection of mechanical transport" it says that the Crossley should carry "wheels, wire, twin, detachable, with dummy hub". Also " two tyres, covers, outer 920 X 120MM" and "two Tyres, tubes, inner 920 X 120 mm" "fitted to spare wheel". Hopefully that answers the question. That will teach me not to jump to rash conclusions. Apologies all round for garden path, leading up of.
Tim (too)