Last night the local bicycle commuter association had winter cycling pioneer Roger Cowles discuss his first rides on the Iditarod trail in the late 80's. He and his friends tried a number of radical designs including replacing the front tire with a ski. Ultimately he had to custom-build his own bike for the deep snow, lacing six wheels together, and here it is in the flesh:
I did not get to ride it home, sadly. He made the center tire slightly prouder than the other so that it could ride on that tire on the flats. The design was so stable he could ride it at extremely low speeds, using those odd handlebar extensions to rest and to help pus through the deep snow.
His original quad design featured a Sturmey Archer five speed internal hub.
Roger had a lot of entertaining tales about his time on the trail, including mushers who thought he might be an escaped mental patient.