FOREMAN, N.D. – With new air drills approaching the 100 feet mark, tractors in the 500 to 600 horsepower range are becoming more commonplace. While bigger drills and 50,000 pound tractors solve a lot of problems, they also create some.
Tires that handle 400 hp just fine can fail when installed on the heavier new tractors in the 500 plus hp range. Tire frustrations have forced some farmers to switch to rubber track tractors. Others continue searching for bias-ply or radials that perform well in the field yet hold together when the going gets tough.
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One Band-Aid solution has been to raise tire pressure, which supports the additional weight and stiffens the sidewall. However, higher tire pressure has a down side. The stiffer, harder tire causes more soil compaction and slippage. Tire slippage burns more diesel fuel, digs deeper ruts and causes the tractor to get stuck in soft spots.
In the days when diesel was cheap, tire slippage was not a big cost. At today’s fuel prices, 10 percent tire slippage means a 10 percent increase in the fuel bill.
Michelin thinks it has a solution. Its engineers in France and North America have developed a radical new design for agricultural radial tires, which they call Ultraflex because the sidewalls are extremely flexible.
Michelin says Ultraflex tires can operate at inflation pressures 20 percent lower than the company’s standard MachXBib radials. When run at the same pressure as standard radials, Ultraflex can carry 20 percent more load.
The Ultraflex also creates a 22 percent larger footprint compared to a standard radial agricultural tire. This lets the tire transfer more power to the ground for increased traction and better fuel economy.
“An agricultural tire under load needs to flex as much as possible to maximize the contact patch and minimize soil rutting and compaction,” said Kevin Lutz, manager of ag technical support for Michelin.
“The deflection zone determines how much a tire can flex. When you look at the cross section of a tire, the deflection zone is the vertical space that runs roughly from the bead of the tire to the point where the sidewall joins the crown.
“Tires with Ultraflex have a much greater deflection zone than standard radials.”
Lutz said the new technology is such a big departure from standard radial ply tire design that the U.S. Tire and Rim Association has created a new classification called IF, standing for increased flexion.
The new tires have four structural characteristics that differentiate them from standard radials. The obvious difference is that the tires have a new carcass profile that creates a bigger deflection zone.
In addition, they have a flat crown profile, a special new rubber compound and reinforced shoulders that reduce casing distortion and help the tire absorb deformations.
In North America, the Ultraflex tires will be sold as Michelin Axiobib radials.
They are available as an option on Challenger MT900B four-wheel drive tractors and will be available on the aftermarket later this year in seven common sizes.
Lutz said the price for Axiobibs will be 15 to 20 percent higher than for the company’s standard MachXBib radials. The new tires carry a D rating, which means they are approved for road speeds up to 40 mph.
Michelin is so confident in the new Ultraflex technology that last month it announced it will no longer manufacture bias ply ag tires for either its Michelin line or BF Goodrich line.
Although radial tires represent about one third of the ag tire market, Michelin said the rising popularity of radials will eventually make bias ply ag tires obsolete. The trend is driven by the radial’s greater load-carrying capacity, reduced soil compaction and better traction.
