More Horses, Different Tires

Larger-volume tires may benefit today’s bigger field tractors.

Like it or not, the trend in row crops is for larger farms, less labor and higher input costs. Equipment manufactures heed that fact by producing larger tractors and pushing for efficiency. Same goes for tires.

Kevin Lutz, the technical manager for Michelin North American Agricultural Tires pointed out that John Deere’s 8530 checks in at 275 PTO horsepower. The top Case IH and AGCO field tractors are in the same power neighborhood.

“And Kinze Manufacturing and other seeding equipment companies offer planters in working widths of 90 feet and more. As equipment continues to increase in size, this trend is shifting the traditional paradigm regarding agricultural tires,” said Lutz.

The shift comes because soil compaction plays a large role in limiting or reducing yield in row crops. Figures provided by Michelin (via Iowa State studies) show yield reduction by compaction of 4 to 6 bushels per acre in corn and 2 to 3 bushels per acre in soybeans. With existing and new equipment, the most practical way to reduce compaction is with proper tire selection and inflation.
 
Radial tires are designed and manufactured to carry extreme weights at low inflation pressures, allowing for a larger footprint that spreads the weight over a broader area. More surface area means reduced pressure placed on the soil.

One Iowa State University study showed that continuous corn grown on alluvial soils farmed with equipment exerting a maximum surface pressure of 6 psi, yielded 9 bushels more per acre than corn grown using equipment exerting surface pressure of 16 psi. In today’s high-fuel, high-commodity-price scenario, that extra yield is critical to profit potential.

Bill Casady, Commercial Ag engineer at the University of Missouri is inclined to accept compaction to some extent.

“Compaction is a way of life,” he likes to say. But just because a force of physics is at play in your fields isn’t reason to give up the fight, Casady pointed out.

“The wider footprints we see from radial tires are a good approach for tillage operations,” he said. “Think about how wide the tires on a combine are. The reason for such wide tires on combines is that we need to distribute weight without compaction.”

Of course, the difference between combines and field tractors is that combines are designed for wider rims.

“That’s why I think if you can get the bigger footprint for a tillage situation in which you’re not concerned about where the tractor is traveling in the field, high-volume radials are a good option,” said Casady.

Lutz said that the most cost-effective option for upgrading to larger-volume tires on existing equipment is to upgrade worn tires with something like Michelin’s XM108 radials because you get the benefits of high-volume radials and their larger footprint without having to change rims. The XM108 radial also features a large air chamber that allows it to carry heavier loads at the same or lower inflation pressures compared to standard-profile radials.

“Wider tires on the same rim saves the cost of having another set of rims. And wider tires won’t change the tractor’s performance in the sense that moving to higher profile tires does,” said Casady.

“Higher profile tires provide a larger foot print. And in some senses, because the foot print is longer instead of wider, it’s a better option. A longer, but more narrow track means that compaction is reduced in total weight per square inch, and, because the footprint is longer, total area of the field under pressure is reduced. However, you incur the cost of new rims and the higher profile can affect tractor performance as concerns gear ratios,” said Casady.

Compaction may be a way of life by Casady’s way of thinking but it can be partially addressed through radials. “They will be more efficient, and that’s a key thing in today’s input environment. You will get more power to the ground using less fuel,” said Casady.
 
Lutz said performance and efficiency are behind what he called a “shifting paradigm” in ag tires. “Most farmers have typically selected tractor tire sizes that accommodate 30-inch row spacings, like the 18.4 R38 a few years ago or the 480/80 R46 that is very common today. But are these tires going to deliver the peak performance, productivity and efficiency you really need? The reality is if you’re not using that tractor for post-emergence applications, such as cultivation or pulling a sprayer, there’s no reason why you can’t move up to a larger-volume tire that’s going to deliver a longer, larger footprint and better overall field performance.”

While Casady believes radial tires can reduce compaction, he believes that controlled traffic in fields is ultimately the way of the future.

“With RTK and GPS, the way forward against soil compaction will be in controlling traffic to specific areas of the field.” But that will be a little more complicated than switching tires.

Tires aren’t the only answer

Fight compaction on your farm giving soil a high consideration in overall management:
• Plan tillage operations to avoid wet fields.
• Reduce tillage.
• Confine traffic to specific paths.
• Encourage drainage to reduce areas of standing water.
• Rotate crops with different root growth habits.

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