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Top-yielding tires

Skimping on tires or ignoring the value of tracks could be crimping your yields, and profits.

In some circles, Francis Childs is a legend. The Manchester, IA, farmer dominates national corn yield contests. Last year, he won with a 394-bu./acre corn yield, which came from fields planted to continuous corn for 30 years.

Yearning for 400 bu./acre this season, Childs anxiously walks his fields, spade in hand, looking for soil compaction. He's done this for years, checking fields up to 60 times a summer and spading to see where compaction lies. These days, his soil is loose and easy to cut through, making it prime for plant growth.

Childs has achieved this soil status by making sure his field equipment does not compact the soil any more than his boots do as he walks across the field. "It is real important to keep compaction to a minimum and in turn build a real good root system quick," Childs says.

Compacted soils reduce crop yields. Childs claims that the key to preventing soil compaction is to equip field machinery with properly sized radial and flotation tires at low inflation pressure. As a result, he spends his money updating tires while making do with older equipment. He works his fields with a 20-year-old tractor equipped with dual radial tires and harvests his bumper crops with a 20-year-old combine, outfitted with expensive flotation tires. The duals are inflated to 9 psi and the flotation tires to 15 psi. At these pressure levels, Childs sees very little compaction on his 320-acre farm.

Important buying. Equipment manufacturers agree with Childs' advice: Don't skimp on tires. "It is an up-front buying decision and it is the most important money to spend," reports Jack Wiley, principal engineer, Deere & Company. "Growers should not try to use a tire as a means of reducing the cost of a tractor."

Not only do improper tires cause compaction, but mismatched tires sap power and fuel efficiency from tractors. A good transfer of power from high-horsepower engines to the ground cannot occur when tires are too small. Slippage and power hopping can result. Many growers already know this, Wiley says, but some still try to save money with smaller, cheaper tires.

As tractors grow in size and power, tires also must grow. "The more power you have, the bigger the tire, and that means both in height and in internal air volume," Wiley explains. "The more power you have to deliver, the more footprint you need to deliver power to the ground."

Answering the call. Tire manufacturers are answering the demand for bigger tires. Firestone and Goodyear are offering new radial tires this year that stand 81 in., the tallest ag tire available. These new tires are intended to handle 4-wd tractors with 400 hp and up.

"As the horsepower goes up and the need increases for low ground pressure during seed preparation, we're going to see taller and wider tires," reports Dave Weed, Goodyear application engineer.

These tires must be kept at lower inflation pressures to reduce compaction. Weed recommends getting tire pressures down in the 6- to 10-psi range.

Major tire manufacturers also are offering new 50-in.-wide tires for combines and implements such as grain carts. Larger combines with more grain storage and bigger grain carts demand wider flotation tires to keep compaction low.

Check tire charts. If you are concerned about compaction, you need to look for a tire that can run at low pressures, reports Kevin Lutz, manager of technical support, Michelin. He suggests you check tire manufacturer charts that show maximum inflation levels for different tires and account for equipment weights, load weights, speed and torque. Then you should select the tire that allows the lowest inflation but is still correctly sized for the tractor.

"Buy the biggest tire you can for a machine without over-tiring it," Lutz says. "Normally most farmers buy tractors with tires that are too small. This results in higher air pressures, more soil compaction and lower tractor efficiency."

New tires will not do it all, though. Equipment company experts maintain that no flotation tire or dual radial can prevent compaction in wet fields. Moist or wet soils, particularly clay soils, will compact under any pressure. "The most important thing anybody can do to control soil compaction is to stay off it when it is too wet," Wiley says.

Track advantages. "Tracks allow you to go out in wet fields a little earlier," Wiley adds. "In terms of flotation and the ability to stay up on wet soils and not get hung up, tracks are superior. However, you can still cause compaction by running in fields that are too wet."

Tracks are known for low compaction, reports Dave Janzen, ag research program manager with Caterpillar's Machine Research Division. The company's crop yield research shows that tractor axle loads should be around 5,000 lbs., and track area should be large enough to provide 6 psi for the critical spring planting operations. Some yield gains are available with ground pressures of 4 psi. But the most critical parameter is axle weight. "Farmers must reduce axle weight if they want the biggest yields," Janzen maintains.

Tracks offer other advantages for cutting compaction, such as reducing traffic in the field. "One way to get rid of traffic is to get rid of duals," Janzen says. "Tracks will cut traffic in half."

Interest in tracks is growing, he adds, especially for higher horsepower tractors. "We feel the majority of high-horsepower tractors will eventually be on tracks," he says.

The company encourages growers to look at the cost of tracks from a cost-per-acre or cost-per-bushel basis, and not the initial purchase price. "Tracks are cheaper to run per bushel because there is less compaction and the fields produce more," Janzen asserts.

Narrow-row dilemma. While tires are getting wider, corn and soybean rows are getting narrower. Tire manufacturers are meeting that demand by also producing narrower and taller tires.

"We're already down to 9 in. wide," reports Goodyear's Weed. "But when you make a tire narrower, it still has to have axle clearance, so we're pushed to bigger and bigger wheel diameters. We've gone from 46-in. diameters to 54-in. in just a couple years." He expects this trend to continue.

But compaction becomes a problem because the inflation pressures are high. Single tires may require 35 psi in the field. Some growers put on duals and even triples to lower compaction.

"But there are engineering limits when you start hanging tires out that far [with triples]," suggests Ken Brodbeck, Firestone engineer and OEM sales manager. "There's a lot of leverage on the bearings. It can be a challenge."

Brodbeck says that, as a result, a few growers with narrow rows are going in the opposite direction. They use radial dual tires producing 7 to 9 psi and plant right in the tracks. The low pressure allows plants to grow through the tracks and yields aren't reduced, he says.

Buying index. For growers who want to replace tires on a tractor, a new index should make the purchase easier.

Tractor and tire manufacturers developed the index a few years ago, but it is only now being widely used. It is a mathematically derived number that represents an increment size step, Weed explains. The index helps growers determine what front and back tires match so the proper gear ratios are maintained.

Tires are grouped in families based on a rolling circumference index (RCI). If a grower wants to replace tractor tires having an index of 47 on the rear and 42 on the front, replacements should have the same index numbers. If he wants to purchase a tire with a different RCI, the increment of change must be the same for front and back.

"The RCI is a guideline for either going to different widths at the same diameter or different diameters," Weed explains. "It should make the whole process more efficient and give you a quick reference to what the front and rear relationship needs to be on a tractor."

What's ahead? Tractor and tire manufacturers expect the trend to larger, more powerful equipment to continue. "Nobody is telling us that they want less power," Wiley quips. "They always say they want to have more power."

If growers want more engine, they will also need more tire.

"Every time we come up with a new size, everyone says that will be the end," Weed says. "But will it ever end? Not necessarily. I'm not one to say technology has reached its limit. But if you look at the 81-in., the next increment is 6 in. Will we get there? I can't imagine us not getting there."

While tire manufacturers are continuing to increase the size of agricultural tires, they also are working to make them more road friendly at higher speeds.

"The requirement to drive faster on the road is happening all over the world," Wiley says. "That means we must have more perfectly round tires and wheels and mounting systems to provide a smoother ride."

In the meantime, growers like Childs will continue updating with new radial and flotation tires to ease compaction and build yields beyond 400 bu.

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