Top Crop Manager

Tire performance to match increasing horsepower tractors

New sidewall technology improves flex.

November 26, 2007  By Top Crop Manager

The next time you are kicking tires at a farm show or your local dealership,
you might be surprised at how the reaction from the sidewall is different than
you expect.

The tires have flat crown profile and special rubber compound.

Michelin has introduced its Ultraflex tire technology with its Axiobob tires
on original equipment high horsepower tractors in 2007. The new design allows
tires to operate at inflation pressures as much as 20 percent lower than standard
radials or carry up to 20 percent more load at the same inflation pressures
as standard radials.

Growers are becoming accustomed to seeing bulging cheeks of radial tires on
properly loaded tractors. It is this flex that allows the tire to maintain full
tread width on the ground while expanding the footprint of the tire along the
line of travel. The bigger the footprint, the lower the ground pressure and
the greater the traction. The lower the ground pressure, the lower the soil


The challenge for tire and tractor manufacturers has been to keep tire inflation
pressures at eight and six pounds per square inch (psi), front and rear, while
tractors have been getting bigger. They reckon optimum performance comes from
100 pounds of load on the ground from every horsepower unit available. So a
500 horsepower tractor needs 50,000 pounds. The advent of 570 horsepower calls
for 57,000 pounds on the tires, so the challenge was to expand the tire footprint
so that inflation pressures could be kept as low as possible.

With its Ultraflex tire, Michelin has increased the proportion of the tire
sidewall that flexes, hence the designation IF (for increased flexion). The
deflection zone, between the bead and where the sidewall joins the crown of
the tire, is substantially greater than on a standard radial. In the process,
the tires also have a flat crown profile and special rubber compound to improve
service life, and reinforced shoulders to reduce casing distortion, which helps
endurance. Also, the new carcass profile that increases the deflection zone
enhances the tire's capacity to absorb surface undulations, thus improving ride.

These tires are new and there is not a great deal of 'service life' experience.
However, Michelin expects users will see improved tractor productivity, better
tire life, more comfort and lower compaction. The tires will come at a premium
cost, but it can be justified, says Ag Technical Support manager, Kevin Lutz,
for Michelin.


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