Since tracks were introduced to agriculture, their makers have commonly claimed reduced compaction and enhanced traction compared to wheeled equipment. In recent years, tire technology has come a long way in leveling the playing field in both regards.
"When we look back at agriculture post World War II and even Korea, many tractors were on steel tracks for the traction they offered," said Michael Vandel, marketing segment manager, Michelin North America Agricultural Tires. "Wheeled equipment was introduced to try and match the traction offered by those tracked machines with new and bigger tires."
The smoother rides and ability to drive wheeled machines on roads, combined with the improved traction, pushed track equipment to the side of the field. In recent years, track tractors have made a comeback, with improved suspension and rubber cleats replacing steel and reducing the need for transport between fields.
Although traction with track vehicles no longer offered a significant advantage over wheeled equipment, tracks' impact on soil compaction did. Spreading out the weight of the tractor and its load over a longer footprint became a major competitive feature as researchers identified yield loss due to compaction.
"Tracks have made a comeback in some markets," noted Vandel. "Growers in those markets have moved from bias tires straight to tracks."
In response to grower concerns, tire companies introduced competitive technology. Size, width and load carrying capacity have all increased significantly to increase the footprint and spread out the load while maintaining traction.
"The longer the footprint, the less the compaction and the more traction you'll have," said Vandel.
However, he pointed out that footprint alone can be deceiving."While the result may be only six psi across the total footprint, the pressure actually increases at the drive wheels and bogey wheels."
Vandel compared that with properly designed new radial tires like those with Michelin Ultraflex technologies. How well the casing deflects and spreads the footprint determines how much pressure is on the footprint. He noted that the industry has reached the point with some tires where one psi in the tire equals one psi on the ground, consistent across the footprint. He points to Michelin AxioBibs as having that 1:1 ratio.
The AxioBib represented a new tire category in 2006 with the increased flexion (IF) design that allowed the sidewalls to flex more than other radials, thereby increasing the footprint. Firestone introduced its first IF tires (AD2 technology) in 2010. Michelin introduced very high flexion (VF) SprayBib VF tires that same year. They allowed for a decrease of air pressure of up to 40 percent compared to a standard tire of the same size.
Meanwhile, Goodyear expanded its Optitrac radial farm tire line with the R+ advanced flexion design. The European-originated R+ design allows field speed dependant load increases that can be more than offered by IF and VF designs. And so the race for superior and competitive tire technology will continue as load, speed, compaction and cost concerns all continue to increase.
"Tires have come a long way in the past 60, 20 and 10 years," said Vandel. "The SprayBib VF met with overwhelming success in the North American sprayer market, but we are still working on new and updated technology for spreaders. Different needs require different capabilities. We can't look at a solution we have and say that's good enough. We have to look at an application use and the demands it faces and develop a tire that fits."