| As fuel prices soar, AgTech Centre engineers explain how farmers can get better fuel efficiency
With increasing fuel costs squeezing producer margins in already tight times, many farmers are wondering what they can do. One answer, say engineers who have been testing tractor efficiency for years, is to make their tractors more fuel-efficient.
Tractor manufacturers are paying attention to fuel economy, with engines on new models becoming more fuel-efficient each year. The top six selling tractors in Canada in 1995, on average, have the potential to produce 16.5 percent more power on the same amount of fuel as the top six selling tractors of 1975.
However, whether a tractor is 20 years old or rolling off the dealership lot for the first time, farmers can implement a number of fuel-saving measures that will not only reduce fuel consumption, but also prolong the life of the tractor.
Fuel efficiency varies depending on the type of equipment, travel speed and numerous other factors. But one of the pivotal factors in fuel efficiency is tire pressure.
Tire pressure key
On a good day, about 70 percent of the power delivered to the axle translates into power at the drawbar, says Reed Turner, an engineer with the AgTech Centre in Lethbridge. Tires are the conduits through which that power is delivered to the ground. How efficient that delivery is, depends on the condition and inflation pressure of the tires.
"Set tire inflation pressure too high and you decrease that power delivery even further," he says. "Tires should be inflated to the lowest correct pressure allowed by the manufacturer for the load the tires are carrying."
Over-inflated tires will rut soft soils more easily, decrease traction, wear the tread unevenly and strain the tire material itself. Under-inflated tires increase sidewall wear and raise the risk of side buckling and rim slip. "By keeping tire pressure at the correct level, you get a little more tire on the ground and are a bit more efficient with the power delivery," Turner says.
Old tires, big savings
Although everyone likes shiny black new tires, those new tires can increase fuel consumption, says Turner. "New tires usually have longer lugs and unless you're in mud, lugs aren't a good thing."
Long lugs can mean lost energy. Every time a lug bends, the tractor is using energy that does not add to the operation at hand. "So brand new tires with long lugs can be less efficient, unless you're in wet conditions, where the long lugs squeeze more mud out the sides, helping the tractor not get stuck so easily."
Older tires with worn lugs are more efficient at providing power on the ground, translating into better fuel efficiency, says Turner.
Fuel efficiency is also affected by other tire factors, including overloading, type of tire and number of tires used. Overloading causes premature tire wear, excessive soil compaction and increased fuel consumption due to the increased rolling resistance.
It's important to choose the correct type of tire, says Turner, who recommends using radial tires over bias-ply tires. A North Dakota State University study found that properly inflated radials improve traction by six percent over bias-ply tires. Similar results were found in AgTech Centre studies.
Using duals can decrease a tractor's fuel efficiency. Duals increase flotation, but may be unnecessary in good traction conditions. "Typically, when fields are dry and traction is good, the more tires you add, the less efficient your tractor is," he says. "Duals are worse than singles and triples are worse than duals."
Farmers should stay away from triples, advises Turner. "If that much flotation is needed, then the larger radials as duals are more efficient than the smaller
ones as triples. When the soil gets too wet, farmers shouldn't be out there anyway."
Gear up, throttle back
For ideal tractor efficiency, match the tractor power to the load, says Turner. "If you have a 100-horsepower tractor and 50-horsepower load, it's not as efficient as a 50-horsepower tractor and 50-horsepower load."
While nobody would ever buy a 50-horsepower tractor to put on a 100-horsepower load, a lot of people will buy a 100-horsepower tractor to put on a 50-horsepower load, "because you never know when you might need that extra power," Turner humorously observes. "That's just human nature, to buy bigger than you need, whether it's a house or tractor."
When a load requires less than 70 percent of the tractor's power, a farmer can save fuel by shifting to a higher gear and slowing engine rpm to maintain the desired speed. This practice is sometimes referred to as GUTB (Gear Up, Throttle Back). "So the speed is the same, but the gear is higher and the engine is running slower. That loads the engine again and brings it back into that 'sweet spot' where fuel is used most efficiently."
Ballasting for efficiency
Most farmers reach the upper limits of their tractor's power only 15 to 20 percent of the time. With this in mind, weighting the tractor for typical conditions rather than maximum needs will reduce fuel costs.
Farmers usually look at ballasting from a worst-case scenario, says Turner. "If they need to pull 20,000-pound loads for two weeks of the year, they ballast their tractors for that load 52 weeks a year. They might be better off to ballast their tractors for 15,000-pound loads. While that means they could struggle a bit for those two weeks a year, it's more efficient than carrying the weight for the other 50 weeks," he says.
Ideally, farmers should ballast their tractors for specific loads, but it can be a hassle, says Turner. "The key to ballasting is to decide the speed necessary for an operation and the amount of the load. Then set the tractor weight just heavy enough to pull that load at that speed and at an acceptable slip level. The total tractor weight should wind up being 2.5 to 3 times the load being pulled."
When a tractor is over-ballasted, excessive torque can be transmitted through the drivetrain and tires to the ground, he says. That can cause overloads, wear and drivetrain failures. As well, fuel costs are increased from carrying the extra weight and from the inefficient power transfer.
"Over-ballasting is a common farmer error," says Turner. "An over-ballasted tractor will probably feel sluggish, and on top of burning more fuel than it should, may experience premature drivetrain problems."
An under-ballasted tractor wears tire tread at a faster pace because of excessive slip, while never delivering full horsepower to the drawbar, he says. Fuel is wasted because of the extra wheel revolutions to travel the same distance.
When fine-tuning ballast distribution, it's important to consider wheel slip, horsepower and speed. The total ballasted weight for drawn implements should balance as follows:
 | Front | Back |
| 2WD | 25% | 75% |
| FWD | 40% | 60% |
| 4WD | 55% | 45% |
For further information, see Research Update 725, from the AgTech Centre.
Use the right fuel
Another way to cut down on fuel consumption is to use the right fuel for the season, says Turner. "It's not a good idea to use winter fuel in the summer or vice versa."
The density of most diesel fuels is normally 0.80 to 0.874 kg/l for optimum engine performance. Winter fuels are typically at the bottom of that range, with summer fuels near the top.
"All an engine does is convert the energy in fuel into usable power. Since winter fuel is blended lighter to improve its viscosity in the cold, it winds up with less energy per gallon. Winter diesel has around 154,000 BTUs per gallon, while summer diesel has around 159,000 BTUs per gallon. This means that the same amount of winter fuel gives about 3% less power than summer fuel. That may be okay in the winter, but carrying winter diesel over and using it in the summer is not such a good idea."
Running a tractor during the heat of the day also heats the fuel and this can affect tractor performance. Generally speaking, in the summer cooler fuel enhances performance. Some manufacturers now install fuel coolers on tractors.
Fuel factors
Farmers can save on soaring fuel prices by following several additional guidelines.
"When you're not using your tractor, shut it off. Some people let their tractors idle for long periods of time because it's easier than restarting, but that isn't the best for fuel efficiency."
Regular maintenance is important for the life of a tractor and for the safety of the operator. Though some people overstate the effect of regular maintenance on fuel efficiency, says Turner, keeping air filters relatively clean and keeping regular maintenance up-to-date are still sensible guidelines.
But major mechanical problems can significantly affect fuel efficiency. "For instance, if an injector is plugged, you're running on five cylinders instead of six, and that means a big loss in power and efficiency."
To save fuel, farmers have to consider their operations, choose the right equipment and apply the correct practices for their situation. Soil conditions, load, tires, weight, the operator and equipment all factor into the equation, says Turner. |