Are you using a tractor that is bigger than what is needed for some of the smaller jobs around the farm?

Most tractors are seldom operated in conditions when the total power capacity of the machine is required. Therefore, a proven process — the gear-up, throttle-down technique — can be used for greater fuel efficiency.

“This practice is fairly old, but what we find is that some farmers use it and some don’t, and some are still learning about it,” says Bobby Grisso, professor and Extension engineer at Virginia Tech University in Blacksburg, Va.

Although it’s an old practice, the fuel efficiencies that result from it can be significant, says Grisso. He has studied this procedure throughout his career, which included working at the University of Nebraska and serving on the engineering board of the Nebraska Tractor Test Laboratory.

The lab conducts independent tests on nearly all tractors that are manufactured. Its tests support gear-up, throttle-down.

“For large tractors, there have been averages of about 23 percent fuel savings when using the gear-up, throttle-down procedure. With smaller-horsepower tractors, as much as 27 percent fuel savings was recognized,” says Grisso, who analyzes and reviews Nebraska Tractor Test Laboratory tests.

Operators can used gear-up, throttle-down when drawbar loads are reduced, by shifting to a higher gear and reducing the throttle setting for the desired forward speed.

When a farmer is not using maximum power, gear-up, throttle-down will save fuel. Operating tractors in low gears at high engine speeds can increase fuel consumption. “The procedure is used so that engine speed and forward speed are matched in such a way that they are the most energy efficient,” Grisso says.

“If you run full throttle even when don’t have maximum load, you will consume more fuel because the engine is still dumping the fuel in and you’re not using the maximum horsepower.”

The gear-up, throttle-down procedure works best for operations such as light tillage, planting, cultivation and hay raking. Grisso says all tractor manufacturers advocate the process, which does not void warranties.

The practice shouldn’t be used when the power take-off (PTO) is operating, such as during hay harvesting. The PTO will run correspondingly slower when the engine speed decreases and might result in high-torque, which increases the wear and durability of the implement.

Gearing up and throttling down also can damage the engine by creating too much torque.

Grisso says many farmers have tractors that are oversized for many of their tasks or they will often encounter conditions where not as much power is needed. For example, it might be easier tilling in a dry season, requiring less horsepower, rather than tilling in wet conditions.

“Gear-up and throttle-down usually works best at about 65 percent load,” Grisso notes. “Most farmers know if they are utilizing full power and if they should gear-up and throttle-down.”

Farmers need to make sure they’re not lugging the engine when using this practice, he warns. “Periodically open up the throttle, and if the engine rapidly picks up speed, the setting is appropriate. A slow response or black smoke indicates a problem.

“To resolve the problem, operators should shift down a gear or increase the engine’s speed.”

He says test reports from the Nebraska Tractor Test Laboratory for each given tractor can be used as a guide for gear-up, throttle-down.

The drawbar load area of a report lists maximum drawbar load, 75 percent of maximum pull and 50 percent of maximum pull.

“As you look through the tractor test reports, it also lists full throttle and a reduced throttle. It is the reduced throttle that is used in the gear-up, throttle-down procedure,” Grisso says.

“What we have found by doing the gear-up throttle-down at a given load at the same speed is, on average, almost a 23 percent savings when you have a reduction of load of 50 percent. It is a very significant savings over what you would do if you just operated the tractor by keeping the throttle open.”

A couple of tractor manufacturers have introduced variable transmissions that eliminate the need for farmers to manually shift gears in variable field conditions to balance ground speed, load and engine speed.

Essentially, a variable transmission achieves gear-up, throttle-down on the fly.

For other diesel tractor models that are 10-20 years old and are not new enough to have a variable transmission feature, gear-up, throttle-down should be considered.

“For farmers in Iowa, Missouri or around the Midwest, we’ll often see them find a great deal on a large four-wheel drive tractor that they can still match up with their smaller equipment,” Grisso says. “Then, they can run it at 50 percent load, re-adjust by using gear-up throttle-down and can still have the same fuel use as if they were using a small tractor. And, in the end, they have that large tractor when they need it as well.”

To review reports from the Nebraska Tractor Test Laboratory ». edu/testreports.htm

SOURCE: By Ann Marie Edwards, IFT columnist

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