A vehicle called the Tundra Truck employing the endless belt 
concept was built by the Laboratory and tested in 1958 and 1959. Each 
of the two belts was 5 feet wide, had a ground contact length of 28 feet, and 
was smooth on the outside. There were 200 8-inch-diameter bogie wheels to 
provide an even distribution of vehicle weight over the belt area in contact 
with the ground. It was found that the bogie wheels sank into the rubber 
belt approximately 5/64 inch, creating excessive rolling resistance. In addi- 
tion, the length to gage ratio of the belts was 2.71 which made steering 
impossible. It was felt, however, that even if the length to gage ratio had 
been below the 1.9 maximum, the vehicle would probably have had trouble 
in turning. When it was towed by a tractor and subjected to a side force, the 
tracks continued in a straight line and the body moved sidewise causing the 
drive rollers to roll out of the rubber tracks, wedging the tracks against body 
members. 
The vehicle ground bearing pressure was 1.6 psi. On soft mud the 
belt left a flat smooth track, but mud squeezed up on the sides and between 
the tracks and got into the bogie wheels increasing the rolling resistance. In 
addition, a wave of mud formed in front of the tracks due to the bulldozing 
effect. This added resistance stalled the vehicle. 
The rubber belt concept, as developed so far, appears to be unsuitable 
for use in soft muds such as are found on the ocean bottom. 
Low-Pressure Tired Wheel. |n applications where they can be used, 
wheels have several advantages over tracks: low maintenance costs, low rolling 
resistance, easy steering, and high speed. On the other hand, they must be 
extremely large to provide a very low ground bearing pressure. In soft terrain, 
they tend to bulldoze soil. Several low-pressure tires have been developed for 
the purpose of providing low ground pressure or ‘‘flotation’’ for vehicles tra- 
versing snow, mud, and other surfaces where conventional wheels cannot 
operate. In deep water, however, due to the high pressures, the use of an 
air tire would be complicated by the necessity of inflating it at the work 
depth. It could be filled with fluid but this would eliminate its ability to 
provide buoyancy, which may be needed. 
The Terra Tire, made by the Goodyear Tire and Rubber Company, 
is an example of the low-pressure tire. To provide a large bearing area without 
enlarging the wheel diameter beyond practical limits, the Terra Tire is length- 
ened along its axis of rotation so that it is about six feet wide and four feet 
in diameter. From the front, it looks like a large, soft roller rather than a 
tire. Although this provides the required low ground pressure, it violates 
the second requirement for a successful snow vehicle mentioned earlier, 
that of along, narrow bearing area. It has been previously pointed out 
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