Compaction Connection

Low-Pressure Tires Are Path to Higher Yields

Jim Patrico
By  Jim Patrico , Progressive Farmer Senior Editor
A Michelin engineer points out the compaction difference caused by a tire inflated to 22 psi (left) and one inflated to 12 psi. (Progressive Farmer photo by Jim Patrico)

Michelin threw itself an anniversary party this fall. It wanted to celebrate 10 years of making Ultraflex ag tires and invited journalists from all over the world to its the headquarters in Clermont-Ferrand, France. If Michelin hoped to plant one message in those inquiring minds, it might be something like this: Low-pressure tires "are a very versatile and cheap solution to [soil] compaction."

That quote actually came from Peter Mills, deputy vice-chancellor of Harper Adams University, which is located in the English Midlands and currently conducting a 10-year soil-compaction study. Michelin is a cosponsor of the study.

As Mills spoke under a tent at the Michelin testing facility during the media event, journalists had a view of a 30-feet-long, 3-feet-deep pit. It was constructed with laminated layers to compare compaction effects on the soil by two tires. One was inflated to 22 pounds per square inch (psi); the other was inflated to 12 psi.

The difference was striking. The tire with lower pressure seemed to have caused less soil compaction.

The reason is simple physics: Lower-pressure radial tires create a longer footprint in the soil to more evenly distribute the weight of the tractor, combine or sprayer they carry. That causes less pressure psi on the soil.

Early results from work done by Mills and his colleagues suggest that reducing tire pressure can have major economic implications, including an average 4% yield increase using lower-pressure tires. The study also suggests there is a 25-to-1 ratio of benefits-to-cost when buyers purchase new Ultraflex tires.

That's enough to get you to pull out your tire pressure gauge.

HOW IT WAS DONE

Here is a bit more on the research. First, the trials were set up to study the effects of tire pressure in different tillage conditions: deep, shallow and no-till. It also included control-traffic situations. There were 36 plots total, each one 4 meters wide.

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The crop was wheat. Results cited are for one year only, which is perhaps not a statistically significant sample.

In planning their research, Harper Adams scientists were mindful of a study done in the Czech Republic that monitored the percentage of a field covered by ag tires during a typical year in wheat. The study indicated 86% of the surface of a field is touched by tires at some point when deep tillage is used, 65% when shallow tillage is used and 45% when no-till is the practice. Other research shows 90% of the compaction caused by tires occurs in the first pass.

Soil scientists have long agreed that compaction causes yield decreases by inhibiting water penetration and root growth. It also causes the agricultural industry to spend "an enormous amount of money ... on damage we have done," Mills says.

He cited those costs when calculating that during a period of five years, "There is at least a 25-to-1 ratio of increased yields to cost outlay of tires." In other words, "It is very worthwhile to spend a little more on [Ultraflex radial] tires. ... That investment will be paid back in a very short period."

Mills cautioned: "It would be unwise to extrapolate from a site in England ..." to other farming conditions and other crops in different parts of the world. That is why he is seeking partners, especially in North and South America, to do similar studies on crops such as corn.

Low pressure seems to make sense for field work. But what happens when those same tires hit the road? The lengthening footprint effect that takes place in the field with low-pressure radials also takes place on pavement. More rubber on the road generates extra heat, which can lead to shortened tire life. It also can decrease fuel economy and affect handling in negative ways.

LESS THAN PRACTICAL

Michelin used to recommend one tire pressure for all situations. Now, it says, an operator ideally would raise tire pressures as he comes out of a field and onto the road, explains Laurent Le Dortz, a Michelin business segment manager.

Easier said than done.

The process of changing pressures to match situations can be time-consuming, and that's assuming you have an air compressor in the field.

But technology is changing that. Last year, Fendt announced tractors with VarioGrip, a central tire-inflation system (CTIS) that allows the operator to change tire pressures from the cab. At its media event, Michelin displayed an aftermarket CTIS product that used an onboard air compressor to change air pressure with in-cab controls on a grain cart being pulled behind a tractor. "It doesn't make sense to have low pressure on the front [the tractor] and high pressure on the rear [the grain cart]," Le Dortz says.

He estimates that optimizing tire pressure can save 10 to 20% of fuel costs when roading, in addition to preventing expensive soil compaction. Still, the CTIS system Michelin demonstrated has a couple of drawbacks. One, it takes six to 10 minutes to change air pressures, depending on size and number of tires. Also, the system costs about $19,000.

Nevertheless, Le Dortz says, "We think it [CTIS technology] will be a global trend."

DIFFERENCE BETWEEN RADIAL AND BIAS:

Michelin invented radial tires for autos in the 1980s. Radials have more flex than bias tires, and that made Ultraflex technology for ag equipment possible.

Bias tires, which were the standard in the general tire industry for generations, use a construction process that crisscrosses plies (or layers) at a 45-degree angle from the center of the structure. This gives the tires strength, rigidity and long life.

Radials use a construction technique in which plies overlap at a 90-degree angle to the center of the tire. This allows their sidewalls to flex.

Michelin introduced XeoBib tires for tractors in 2004.

It followed that with CerexBib for combines and SprayBib for sprayers. In 2015, it will introduce the CargoXBib for heavy-duty trailers such as grain carts.

(BAS)

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Jim Patrico