Reinventing the Radial

Feb 15, 2007 12:00 PM, By Jodie Wehrspann

Michelin Ag says it has taken radial technology to the next level.

Last month the company rolled out its new IF800/70R38 Axiobib radial tire with Ultraflex technology, first previewed last year at the National Farm Machinery Show (see April 2006, page 38). The tire represents a new category of radials with “IF,” which stands for “increased flexion.” IF provides large-volume tires (those wider than 520 mm) with the additional flex or “bulge” in the sidewall they need to support the weight of new 4-wd tractors — without requiring more air pressure.

The technology, which Michelin has branded “Ultraflex,” allows its new Axiobib tire to run at 20% lower inflation pressures, or carry up to 20% more load at the same inflation pressures, as standard radials. “We think that going from standard radials to Ultraflex could be as big a step as going from bias to radial,” says Kevin Lutz, technical manager for Michelin North America Agricultural Tires.

To illustrate what the new technology can mean for tire buyers, Michelin invited journalists to its headquarters in Greenville, SC, for a two-day training and test drive. The new Axiobib tires with Ultraflex were put on a prototype of AGCO Challenger's behemoth 570-hp MT975B tractor, which will be the largest 4-wd tractor in the world when it goes into production later this year.

Tire anatomy

“We sometimes assume people know a lot more about tires than they do,” Lutz says. “And one of the things we assume they know is what a radial tire is.”

He explains that the radial tire, which Michelin patented in 1946, is made from layers of rubber-coated plies of fabric. The plies are laid side by side at a “radius,” or 90°, to the center line of the tire. Additional material is then wrapped around the top of the tire to reinforce the crown or tread area.

Bias tires, in contrast, are made with plies that are laid crisscross over each other. These plies form both the tread and sidewall. Because all the layers in a bias tire are interconnected, the sidewall cannot flex or “bulge” without shifting the whole tire. In radial tires, because the crown is built separate from the sidewall, the sidewall can flex and the tread can stay planted on the ground.

Sidewall flex is important in tires because it allows for better performance, Lutz says. He says radial tires, known for their sidewall bulge, have been proven to provide superior traction, better fuel economy, better ride comfort, improved handling, and longer life than bias tires.

Market penetration

Because of these advantages, 99% of passenger car tires today and 95% of over-the-road truck tires are radial, according to Michelin figures. Ag tires, in comparison, are only 30% radial because not all farm vehicles require the same level of performance. For example, tires on chore tractors and small combines are still predominately bias.

However, the percentage of ag radials jumps to 90% for tractors over 120 hp. “If you look at the 20% of farmers doing 80% of the production, 90 to 95% of the tires on their primary production tractors are radial,” Lutz says. In those applications, radial tires are critical because of their ability to minimize soil compaction.

Soil compaction is caused from downward pressure. Radial tires create less ground pressure because their sidewall flexibility allows for lower inflation pressures. When air pressure is reduced, the tread of the tire lengthens out, resulting in a bigger footprint. A larger footprint distributes the weight of the tractor over a larger area, thereby lowering ground pressure.

Lower ground pressure reduces compaction, which in turn can lead to higher yields. According to a four-year continuous corn study conducted by Iowa State, corn grown on soil farmed with equipment exerting 6-psi surface pressure yielded 9 bu./acre more than corn grown with equipment exerting 16-psi surface pressure. On a 1,000-acre farm, a 6 bu./acre yield advantage results in $18,000 in additional revenue if corn is priced at $3.00/bu.

Story Continued on Next Page >