Tractor Trendsetters: Low-Pressure Pneumatic Tires
Written By Larry Gay
Until 1932 the farm equipment industry used wood, cast iron, and steel as the raw materials to build tractors and farm machinery. Then in the autumn of 1932, during the depths of the Great Depression, rubber was added to the list of materials when Allis-Chalmers, Firestone, and Goodyear introduced low-pressure pneumatic tires for tractors. This new product was originally known as an “air tire” and was first made available on the Allis-Chalmers standard-tread model U tractor. However, the tire companies quickly made air tires available for other brands of tractors.
The first Firestone tires for the rear wheels were an 11.25-24 size and made with a chevron style of tread. The Goodyear tires were equipped with a diamond-tread pattern. In 1935 Firestone introduced a bar-style lug for more traction. Test work revealed the optimum air pressure was about 12 psi.
In November 1932 at an engineering meeting in Milwaukee, Allis-Chalmers presented the results of its two years of test work to other engineers in the industry. The A-C engineers used graphs, charts, and motion pictures to show the advantages of air tires over steel wheels with spade lugs. However, many of the competitive tractor engineers attending the meeting were not convinced and left the meeting still skeptical of the new concept of air tires.
Farmers too were skeptical about air tires when they were first introduced. However, the tractor dealers and the tire companies were able to overcome this sales resistance by conducting plowing demonstrations with two identical tractors, except one had steel wheels and the other had air tires. The demonstrations proved the tractor with air tires could plow faster with less wheel slippage and provided a smoother ride with less dust for the operator. Also tractors with air tires could be driven on paved roads.
Allis-Chalmers promoted air tires by staging tractor races at the state fairs in 1933. The Allis-Chalmers WC row-crop tractor was tested at the Nebraska Tractor Test Lab in May 1934 with both steel wheels and rubber tires. When it was equipped with rubber tires, the tractor provided more drawbar pull and better fuel economy. Farmers and the tractor industry quickly recognized the advantages of rubber tires and the last Nebraska test of a tractor with steel wheels was in 1938.
Larry Gay is the author of four farm tractor books published by the American Society of Agricultural and Biological Engineers. These books may be obtained from ASABE at 800-695-2723 or asabe.org, click publications and then click history books.