How to calculate your tractor's fuel efficiency
Nov 1, 2008 12:00 PM
Farm Industry News asked Nebraska Tractor Test Lab Director Roger Hoy and Assistant Director Dave Morgan what factors to use to compare the fuel efficiency of different tractors. You can use these parameters to determine how your models rank.
Go to http://tractortestlab.unl.edu. Click on “Test Reports.” The Web site shows all makes and models tested at the lab since 1999. (Hard-copy reports for tractors tested before 1999 are available for purchase. Contact Nebraska Tractor Test Laboratory, Box 830832, University of Nebraska-Lincoln, Lincoln, NE 68583-0832, 402/472-2442, tractortestlab@unl.edu.)
Click on make and model of tractor. This will bring up the corresponding test report.
Check “Chassis: Type” to determine tractor category (2-wd, front wheel assist, 4-wd, or track). This information is included in the narrative text next to the charts on the site. We ranked tractors in two categories: row-crop tractors (2-wd/front wheel assist) and high-horsepower 4-wd/track tractors.
Check horsepower to determine size category. We used PTO horsepower (at rated engine speed) to determine if the tractor belonged to the category of row crop (150 to 200 hp) or high-horsepower 4-wd/track (300+ hp). (See lab chart called “Power Takeoff Performance.”) This is the number used by all manufacturers to verify a claim.
Find the rating of horsepower-hours per gallon. The fuel consumption measurement, horsepower-hours per gallon (hp-hr./gal.), has become the standard used for comparing the efficiency of all agricultural tractor models. Measured directly, it means that burning one gallon of fuel in the tractor at full load and at rated engine speed produces a certain amount of horsepower for an hour. The higher the number, the greater the fuel efficiency; that is, more work is being done with a given amount of fuel.
We looked at that rating in two performance tests: power takeoff and drawbar performance. We used results from the “PTO Performance Chart” to establish the fuel-efficiency rankings. The lab says the PTO rating is a good indicator because it is one that is calculated for all tractors and it is always run at the maximum level. However, results from the drawbar performance test are also included, and depending on how you plan to use the tractor, it may be a better indicator of fuel efficiency for some tractors — for example, the very-high-horsepower tractors used primarily for their brute pulling power of, say, deep tillage implements. On the other hand, if the tractor is used primarily for PTO work, then the PTO rating will be your best indicator because it will not be likely to change or won't be as much affected by the size or weight of the implement the tractor is pulling. If you use the tractor for both PTO and tillage work, then consider both ratings in your decision.
PTO performance is measured at several different power levels and speeds, but for comparison purposes, the factor most farmers are interested in is maximum power at rated engine speed. This is the highest power level that the tractor can sustain over a long term and is measured in horsepower. Newer tractors usually have an operating range that includes maximum power at a speed lower than rated. Also, with modern high torque/constant power engines, the power at rated PTO speed is usually similar to the power at the rated engine speed.
Like PTO performance, drawbar performance is measured at different rates of pull and in different gears. Power measured at 75% of pull at maximum power is a reasonable reflection of performance during typical heavy fieldwork. At 75% of pull at maximum power, you will still have some reserve for heavy spots in the field. We list the horsepower-hours per gallon in “third gear” (to show maximum drawbar pull) and “eighth gear” (to show maximum power).
Drawbar tests are conducted on concrete or asphalt test tracks, which allow for consistency in comparison. As a result, the numbers in the test reports are not exactly the numbers you might get in field conditions.
The drawbar ratings listed are for “ballasted” runs. If a ballasted test was not run, then results from the unballasted test (at 1,800 rpm or the lowest engine speed) were used.
In cases where ratings are identical (for example, Case IH and New Holland 4-wd tractors), only one of the tractors was tested and the results serve for both because there was no performance difference between the two.
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