WEST LAFAYETTE, IND. (Sept. 30, 2009) – Growers who want to get the most out of today’s larger, high-horsepower farm equipment while protecting their soil from damage can benefit from mounting large-volume radials on their tractors and combines, new research shows.

Dozens of Midwestern growers gathered at Purdue University’s Animal Science Center fields Sept. 10 to watch as experts from Michelin North America Ag Tires and Case IH demonstrated how large-volume tires with low air pressures can deliver optimal fuel efficiency and traction and reduce slip and soil compaction. Researchers from Purdue were on hand to explain the effects of soil compaction on crop emergence.

“As farms have gotten larger, tractors and combines have by necessity gotten larger, heavier and more powerful,” says Bob Rees, North American product marketing manager for Greenville, S.C.-based Michelin North America Ag Tires. “Growers using standard tires on larger tractors pay a heavy bottom-line price in reduced fuel efficiency, decreased productivity and greater soil compaction.”

Standard tires slip, hop and guzzle fuel

Working with retired Case IH product specialist Bill Manke and cooperating with Jeff Fields, farm operations manager for Purdue’s Animal Science Center, Michelin conducted ag tire performance tests comparing MICHELIN® Axiobib large-volume radials to a competitor’s standard-sized 480/80R50 farm tire. The tests were conducted on the same 275 hp Case IH 335 Magnum tractor. It was equipped first with the competitor’s standard-sized radial and sent across a field pulling a ripper with five shanks, then seven shanks and finally nine shanks deployed. Then, on unplowed parts of the same field, the same tractor completed the tests on MICHELIN Axiobib radials.

In Aug. 31 tests on the competitor’s standard-sized tires, the tractor pulled the five-shank ripper successfully. But power hop plagued the performance of the standard tires’ efforts at pulling both seven and nine shanks to the extent that Manke declared that the performance was “not acceptable.” Furthermore, average slip for the standard tires ranged from 8.4 percent pulling seven shanks to 12.2 percent pulling nine shanks. Using the standard tires, the tractor’s fuel consumption ranged from 11.1 to 13 gallons per hour.

Large-volume radials grip, sip and pull

In tests on Sept. 1, using the same tractor but using MICHELIN Axiobib radials, a different picture emerged. The Michelin tires suffered power hop for 50 yards once while pulling seven shanks but had no other issues. The highest average wheel slip for the MICHELIN radials was 6.3 percent pulling nine shanks while operating at 1800 RPMs in eighth gear. Other than that, while running Michelin radials, the tractor’s average slip ranged from 1.4 percent to 4.7 percent, significantly lower than that of the standard tires.

Tractor fuel economy also improved on the MICHELIN Axiobib radials, which feature the tire company’s patented Ultraflex™ Technology. The tractor averaged 12 gallons per hour when pulling nine shanks under full throttle in eighth gear, but otherwise ranged in average fuel economy from 8.6 gallons per hour to 11.4.

“The best fuel economy we saw was when we were on the Michelin Axiobib radials and using the Case APM while pulling nine shanks,” Rees says. “We saw fuel economy of .9 gallons per acre, whereas the best we saw on standard tires was 1.1 gallons per acre with an average of 1.2.”

For combines, the proof is in the pit

Michelin and Purdue researchers also devised a way to visibly show the effects of soil compaction. They dug a pit that was 27 feet wide, 12 feet long and three feet deep and refilled it one four-inch layer of pulverized black topsoil at a time, alternating it with thin layers of white stone dust.

“We took a John Deere 9760 combine and equipped it with 650/85R38 Michelin MachXbib radials on the right side,” says Michelin’s Rees. “On the left side, we mounted a competitor’s standard 520/85R46s, which are the same height as our MachXbib radials.”

Tire pressures were set at 30 psi in the standard tires and 17 psi in the large-volume MICHELIN MachXbib radials. These pressures were based on the 6mph cyclic scale that is standard for combines in the field. The combine, which had a front axle weight of 53,200 pounds, was then driven over the pit. A backhoe later dug out half of the pit to expose the ruts the tires left in the soil and show just how much difference there is between the compaction caused by standard tires and the lesser amount left by these large-volume tires.

Cross section makes compaction clear

Farmers gathered round the pit on Sept. 10 as Purdue professor Tony Vyn and Michelin’s Michael Vandal explained soil compaction and its effect on crop emergence. Where the combine wheels had traveled, the alternating chocolate and white lines dipped. Vyn pointed out that the standard tires on the combine left a rut of about 10 inches. The Michelin large-volume tires left a rut of only 6.5 inches. “The primary problem with soil compaction is it reduces the water available to the root system,” Vyn says.

Vyn points out the Michelin large-volume tires left a slightly wider rut – 65 inches vs. 54 inches – because of their wider footprint. “Nevertheless, the standard tires displaced 28 percent more total soil, and the compacted soil layers under the standard tires were deeper and therefore more difficult to subsequently alleviate than with the Michelin large-volume tires,” he says.

Vandal, agricultural segment manager for Michelin, says the difference between 10 inches of soil compaction with standard-sized tires and six and a half inches with Michelin large-volume radials means a significant amount of difference in crop vigor.

“With the extra compaction, your nutrients are going to be restricted in reaching your plants, so you’ll have a less vibrant crop,” Vandal says “If water isn’t restricted, it’s very reasonable to expect plant productivity, and ultimately your profitability will improve. The market always fluctuates. But compaction? Efficiency? These are things we can control and improve, often by making the correct choice in ag tires.”

Rees and Vyn agree that the field day co-sponsored by the ag tire company and the research university, with help from Coogle’s Tire and Case IH, is a perfect example of what can be achieved when the public and private sectors partner.

“This was a great way for the commercial and the academic sectors to work together on the issue of soil compaction,” Vyn says. “The pit was very dramatic in comparison of rut depth between two tires of the same diameters on the outside but with dramatically different flotation properties. I was pleased to see how well the demonstration worked.”