that rolling resistance due to bulldozing is proportional to tire or track 
width. For a given ground contact area, the wide tire has an unfavorable 
rolling resistance. Terra Tires are now made in a variety of widths and tread 
designs for different applications. Some of them have been successful on soft, 
wet soil and snow. 
Goodyear’s Liquid Transporter and the Rolligon air bag made by the 
Albee Rolligon Company, Incorporated, are similar to the Terra Tire. These 
units are made of soft, light materials and tend to ‘’flow”’ over the ground in 
a manner similar to the flow of a viscous liquid, conforming to rocks and 
other hard obstructions as they pass over them. They must be driven from 
the periphery, however, as the soft sidewalls will not transmit power from 
the axle. A powered roller, bearing against the tire periphery, transmits 
power to the wheel by friction. On the ocean bottom, the coefficient of 
friction between the roller and the wet rubber tire, especially in locations 
where they would be lubricated by a film of clay adhering to the tire surface, 
would be so small that practically no power could be transmitted in this 
manner. For this reason, they would probably be impractical for use under 
water, except on a towed vehicle. A Rolligon equipped vehicle has been 
tested on soft snow and found to be unsatisfactory (Mellor, 1963). 
Oblate Wheel. An oblate wheel was laboratory-tested at NCEL in 
1951 (Weiss and Magill, 1951). This model measured 10.6 inches on the 
long axis and 7 inches on the short axis, and was 1-1/2 inches wide. It was 
concluded that this wheel was superior to a round wheel in wet and dry 
sand and would probably be superior in mud and snow. It tended to roll 
itself out of its own rut, rather than having to plow through the soil. It 
appeared that the long axis of the wheel penetrated deeply enough in the 
soil to develop shear deep in the soil mass, going far beyond the contact 
surface between the wheel and soil (Figure 36). Greater drawbar pulls 
were developed by the oblate wheel than by a conventional round wheel 
of the same circumference. This wheel has not been tested operationally 
on a vehicle, but it might prove useful on the ocean bottom. 
Archimedean Screw. Much time and effort have been expended 
to develop a vehicle based on the Archimedean screw for traversing snow, 
mud, and swamp areas. Generally, the concept employs two buoyant 
cylindrical pontoons with conical ends (Figure 37). Encircling the sides 
of the pontoons is a narrow fin in the form of a screw thread around the 
cylinder; a left-hand thread on one pontoon and a right-hand thread on 
the other. The passenger, cargo, and engine space is between the two 
pontoons. The pontoons float on the mud or snow surface, and the 
counter rotating screws propel the vehicle. 
45 
