Larger and larger equipment means higher axle loads and enough inflation pressure in the tires to carry that load.  Unfortunately, those higher pressures can increase soil compaction and result in reduced yields. But new technology in tire design that allows the sidewall to flex under lower inflation pressures can help alleviate the problem.

Lower inflation pressures produce a larger "footprint" which results in improved traction and reduced soil compaction.

PULLING AHEAD: The tractor with standard radial tires inflated at the lower pressure (14 psi) travelled 48.5 feet further on the 1,000-foot course.

Firestone, a manufacturer of this new class of farm tires, recently hosted a field day for customers and dealers near Des Moines, Iowa, to demonstrate the benefits of the "next generation" in farm tires. Firestone's line is called AD² (Advanced Deflection Design). The tires are designed to carry more load at the same pressure or the same load at a lower pressure – or as much as 20% (Increased Flex -IF) or 40% (Very High Flex -VF) more load at the same pressure – as equivalent sized standard radial tires.

Engineers set up two tractors for the field demo – a John Deere 8335R fitted with IF420/85R34 AD² Radial All Traction DT TL R-1W tires on the front and IF480/80R50 AD²  Radial Deep Tread 23⁰ TL R-1W tires on the rear. A John Deere 8310R was fitted with 420/85R34 Radial All Traction tires DT TL R-1W on the front and 480/80R50 Radial Deep Tread 23⁰ TL R-1W on the rear.

FLEX DESIGN: This AD2 tire was inflated to only 10 psi and pulled ahead of the tractor with the standard tires inflated to the minimum required to carry the load.

"This demo is not a horsepower or fuel efficiency test," noted Wayne Birkenholz, Firestone manager of field engineering.  He said the hypothesis for the test is "a tractor fitted with properly inflated AD2 tires will reach the end of a measured course before an equally ballasted tractor fitted with properly inflated standard tires of the same size, pulling an equal load."

Here's how the traction demonstration was set up. One end of a cable was attached to one drive tractor, run through a pulley on the "anchor" tractor and attached to the second drive tractor. As both drive tractors pulled the anchor tractor at the same speed and rpm, the tractor with tires delivering more traction moved ahead of the other.

Birkenholz ran two demos for the group. Objective of the first demonstration was to show the importance of properly inflating a tire to match the load. "Over inflation of tires is a common occurrence," he notes.

Tires on the first tractor were set at 14 psi, which was the correct pressure for the load. The second tractor's tires were over inflated to 30 psi. Both tractors ran in 7^th gear at 2,000 rpm, or about 3.5 mph with front axles engaged and the differential locked. Both tractors stopped simultaneously when the first tractor's rear wheels reached the finish line. Then the distance between the rear axles was measured.

LARGER FOOTPRINT: These side-by-side graphics demonstrate the larger tire footprint achieved with lower tire inflation pressures. The tire inflated to 30 psi had a footprint length of 22 inches while the tire inflated to only 14 psi had a footprint of 25 inches.

The tractor with tires properly inflated travelled 48.5 feet further on the 1,000-foot course. "In other words, the tractor with tires inflated to match the load had 4.8% better traction," explained Birkenholz.

The objective of the second demonstration was to show the difference in traction between Firestone's AD²  radial and Firestone's standard radial. Matching the load to inflation pressure the AD² tires were set at 10 psi. The same size Firestone standard radial tires were set at 14 psi. Again, the tractors ran in 7^th gear at 2,000 rpm or about 3.5 mph with front axles engaged and the differential locked. At the finish line the tractor with the AD² tires travelled 11.5 feet further on the 1,000 foot course or about 1.2% traction advantage. "Soil type and moisture can have an effect on efficiency," said Berkenholz. "Typically, we see a 3-5% gain at this rate."

Firestone's AD² brand tires are designed to be used on tractors, sprayers, implements and harvesting equipment.