Fuel savings rationale for flatter tires

Looser soil, better yields | Running at the lowest recommended pressures saves fuel and reduces compaction

HANOVER, Germany — Running on flat tires used to be considered a sign of a lazy farmer.

However, German researchers have shown that flatter tires can result in fatter wallets for farmers.

Research has supported the commonly held view that tires are better able to transfer power to the field when the pressure is lower.

However, not everyone has equated that idea with improved fuel efficiency.

“What matters most for fuel efficiency is getting power to the ground. When you have high pressures you can manage high horsepower, but you will be fueling up a lot more often,” said farm machinery engineer Georg Ebbeler.

“You just end up moving some dirt around, and that is a problem, too.”

Ebbeler and his colleagues from the South Westphalia University of Applied Sciences in Germany tested the theories about lower pressure, soil compaction and fuel use.

“We also found that the reduced soil compaction was important to improving yields as plants’ roots get more opportunity to grow,” he said.

“That means bigger, healthier plants and fewer field losses.”

Last week, the engineers and agricultural science students staged a large track at the Agritechnica farm show in Hanover that was filled with sand to simulate a field. It was wide enough to accommodate several passes of a tractor.

They pulled one tractor with another, back and forth through the track in a set gear and at a set speed. One pass was done with tires at a recommended 23.2 pounds per sq. inch of inflation and a second, parallel pass was completed a lower one at eight pounds. The tire pressure was managed with a central inflation system.

Fuel was fed into the tractor every half hour during the day for seven days from a pair of tall graduated cylinders so that the show crowds could easily monitor fuel use.

The extension research performed on the fairgrounds matched what had been done in the field.

“We saved 13 to 14 percent (on fuel) here in our test track. We got similar or better fuel savings in our field trials,” Ebbeler said.

“There are several factors. One is that these special tires are made to elongate the tread as the pressure falls, and that means the load is carried over a larger, but not much wider, area.”

The lower inflation keeps the tires from sinking into the soil as much, which reduces the amount of “bulldozing” that occurs as dirt is forced into a mound in front of the tire.

“The tractor must then climb up hill all the time,” he said.

“You are having to constantly dig your way out of a hole, and this takes power that should be used moving the load of the implement.… Moving that dirt around in the field causes compaction.”

Reduced slippage on the fairground’s test track also proved to be similar to that of the field research.

“We found that if we cut the pressure in half, using the high flexion tires we could reduce slippage by up to 20 percent. That is a 20 percent reduction in time in the field,” he said.

“At 50 euro ($70) per hour for a tractor and labour, 20 percent would save you a lot money … but most farmers don’t have central tire inflation. That is where new high (deflection) tires come in. You can run the same pressure on the road without risking damaging the sidewalls or losing control of the tractor at higher speeds on pavement.… One pressure for both jobs. The Bib tires from Michelin were the ones we used. They have them for small, large tractors, combines and sprayers, but many companies now offer this technology.… I know lots of farmers won’t just go out and buy a new set of tires just for the savings in fuel and time, but they should do the math and see how long it might take to pay for the technology on their own farm. It might pay off faster than they think, especially on big farms like in Canada.”

To view a video of the demonstration, visit www.producer.com/sections/video.

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