Using Tractor Test Data for Selecting Farm Tractors

The Nebraska Tractor Test Laboratory (NTTL) at the University of Nebraska is the official U.S. tractor testing station for the Organization for Economic Cooperation and Development. This laboratory has the responsibility for testing all models of tractors sold in the state of Nebraska, and it publishes the results of all tests it conducts. It also tests tractors manufactured in the United States and sold in international markets.

The test reports published by NTTL can be extremely useful for selecting tractors or for comparing the performance of different makes and models of tractors. For example, when farmers are in the market for a tractor, the performance data in the NTTL reports can be used to select a tractor that will meet their needs. These reports can also serve as an effective tool for making tractor sales. Dealership personnel can use the performance data to compare their products to those of their competitors.

For either application, familiarity with the content of the test reports as well as how to use the information are critical. Therefore, this fact sheet was developed with the following specific objectives:

1. To familiarize farmers and other users with tractor testing and the Nebraska test reports.
2. To demonstrate the use of tractor test reports for the selection and performance comparison of farm tractors.

Nebraska Tractor Test Laboratory

The NTTL is a member of the Organization for Economic Cooperation and Development, and it is one of 27 such testing laboratories in the world. The organization requires that all tractors manufactured in member countries be tested in the country in which they are manufactured, following its guidelines. Based on an established agreement between member countries, test reports approved by OECD are accepted by all participating countries.

Tractor Tests

The purpose of the tractor tests is to collect data that can be used to assess the performance of different makes and models of tractors. For this reason, all tests are conducted under the same or similar test conditions and procedures. Tractor tests are generally conducted to assess the power-takeoff (PTO) performance, draw-bar performance, hydraulic lift capacity, and hydraulic system pressure and flow. In addition, sound level measurements are taken at operator and bystander locations.

PTO performance tests are conducted with a dynamometer attached to the tractor PTO. The purpose of the dynamometer is to apply varying loads through the PTO and to measure the power generated by the tractor. These tests (fig. 1) are conducted at an ambient temperature of 75 degrees Fahrenheit and a barometer reading above 28.5 inches of mercury. During tests, when the tractor performance has stabilized, the data is recorded at predetermined intervals.

The load applied by the dynamometer follows the operating curve of the engine at full throttle. Data collected include torque, rpm, power, and fuel consumption. A series of PTO tests are conducted at rated engine speed, standard PTO speed (either 1,000 rpm or 540 rpm), engine speed where maximum power is produced, varying load, and maximum torque.

Drawbar performance tests (figs. 2 and 3) are conducted in all gears between a lower gear below the one that provided maximum drawbar force (without exceeding a wheel slip of 15 percent) and a maximum speed of 10 miles per hour. Using each gear at full throttle, the load is increased until maximum draw-bar power is achieved. Engine speed, wheel slip, and fuel-consumption data are recorded when test conditions are stabilized.

Drawbar tests are also conducted with partial loads at 75 percent and 50 percent of the maximum drawbar load (at rated engine speed). These partial-load tests are also conducted at reduced engine speeds (selected by the manufacturer).

Hydraulic lift capacity and flow tests are conducted to determine the maximum lift capacity of a hydraulic system through the full lift range. The lift capacity in the report is 90 percent of the maximum load carried through the full lift range.

Additional tests are also conducted to determine the pressure-flow relationship of the hydraulic system for supplying power to external actuators (such as motors or cylinders). Reports include data on delivery rate, pressure, and available power.

Sound level measurements during performance tests are taken at operator and bystander locations. For the bystander measurement, readings are taken by locating the microphone 25 feet from the centerline of the tractor. Sound levels are recorded using the “A” scale in the sound level meter and are expressed in terms of decibels (A) or dB(A). The A scale is a filter that responds like a human ear.

Nebraska Test Reports

Nebraska law mandates that NTTL publish the test results on all tractors sold in the state of Nebraska, which may include tractors tested by NTTL or by one of the other OECD partners. A full OECD report is generally 30 pages long. The NTTL summarizes and publishes the test results in two formats (to order, see contact information in the Additional Resources section).

1. The first format is a booklet (4 inches by 6.5 inches) published annually with limited performance data on all tractors available for sale in Nebraska that year.

The summary booklet includes approximately 400 tractor models from different manufacturers.

2. The second format is a more-detailed report (typically two to six pages in length), covering individual tractor test results.

Samples of both reports are included in appendixes A and B, respectively, and they are discussed in the following paragraphs.

The cover page and a typical page from the summary booklet are exhibited in appendix A. A typical page in the summary booklet (appendix A-2) provides the summary of test results of two or three of a manufacturer’s tractors (in this case, New Holland). The summary includes information on tractor model, limited engine and chassis specifications, PTO and drawbar performance data, sound level, three-point lift capacity, and hydraulic system parameters. The summary booklets are particularly useful for an initial review of the performance of tractors of different sizes that are produced by different manufacturers.

When the initial review generates interest in a particular tractor model, such as New Holland’s model TS135A (appendix A-2, col. 3), the user can obtain a summary report specific to that model tractor (the second report format). A copy of this detailed report specific to model TS135A is shown in appendix B.

The first page of the summary report (appendix B-1) provides information on test number, make and model of tractor tested, and transmission. It also includes results of PTO and drawbar performance tests, in addition to tractor specifications in a column located on the right side of the page. Fuel consumption is reported in three different ways: gallons per hour, pounds per horsepower-hour, and horsepower-hours per gallon. Fuel consumption expressed in terms of horsepower-hours per gallon is useful for comparing fuel consumption of tractors of different sizes. PTO tests at varying power levels simulate a wide range of field operations using the tractor.

The drawbar performance data at the bottom of appendix B-1 often continues to the next page. This data includes drawbar power and pull, forward speed, wheel slip, engine speed, fuel consumption, temperature, and relative humidity conditions at maximum, 75 percent, and 50 percent pull at maximum power. The tests at reduced engine speed also include similar data at various travel speeds.

Power measured at 75 percent of pull at maximum power may represent a typical operation with heavy loads, such as primary tillage. At 75 percent pull, the tractor may still have some reserve power to overcome unexpected overload situations. The average fuel consumption at 75 percent and 50 percent pull may represent tillage and seeding operations, respectively, on small-grain farms. Similarly, the average fuel consumption at the 50 percent pull tests can serve as a good estimate of fuel consumption when tractors are used in row crop farming. This distinction between small-grain and row crop production is made because more efficient tractor-implement matching is possible for small-grain production. For small-grain applications, selection of implements to utilize the available tractor power can be accomplished more easily. However, the same conclusion may not be true in the case of row crop implements.

Tractor tests are conducted on hard surfaces — concrete or asphalt tracks — for consistency between tests. Therefore, the performance data recorded during these tests can be significantly better than what can be expected under normal field conditions.

Sound level, tire, and weight information are provided at the bottom of appendix B-2. Tractor sound level at the operator’s ear location is critical because the Occupational Safety and Health Administration (OSHA) has strict sound level and exposure-time regulations. For example, OSHA permits an eight-hour exposure period if the sound level in the work area is 90 dB(A). A 3-dB(A) increase in sound level doubles the sound-pressure level. Therefore, for every 5-dB(A) increase in sound level, the permissible exposure time is cut in half. In other words, at 95 dB(A), the allowable exposure time is only four hours. It is not uncommon to have tractor sound-level reaching 95 dB(A).

If the tractor tested has front-wheel assist, additional drawbar tests with the front-wheel assist disengaged may follow. The last page of the report (appendix B-3) is devoted to three-point hitch performance data, hydraulic system parameters, and hitch dimensions.

Published tractor test results can also be used for estimating annual fuel consumption by knowing how the tractors are used during the year (see Predicting Tractor Diesel Fuel Use, Virginia Cooperative Extension publication for more details). This information is particularly useful for budgeting and management purposes.

Fuel savings are possible with practices such as “gear up and throttle down.” The drawbar performance data (appendix B-1) documents the fuel savings possible with the practice of gear up and throttle down for light load conditions (for more details of using this technique, see Gear Up and Throttle Down to Save Fuel, Virginia Cooperative Extension publication). The drawbar-performance categories that include the phrase “at reduced engine speed” can be compared with the tests conducted at full throttle at the same load level. The specific fuel consumption (horsepower-hours per gallon) for the tests at reduced engine speed will always be more efficient than the values for the full throttle with the difference being expected fuel savings.

Depending on the engine design and other controlling factors, the gear up and throttle down technique can provide fuel savings in the range of 15 to 30 percent.

For the tractor operating at 50 percent load (appendix B-1), the potential savings is about 16 percent (11.67 hp-hr/gal from the reduced throttle versus 10.05 hp-hr/ gal at full throttle). The annual fuel savings from the use of this technique can be estimated by multiplying the total number of hours the tractor is used annually for light-load operations, by the fuel consumption difference.

Using the Test Reports for Tractor Selection

Many factors are taken into consideration in the selection and purchase of a new tractor. These may include factors such as types of jobs to be performed, price, proximity and reputation of the dealership, desired power output at the drawbar and PTO, hydraulic system capacity, and fuel efficiency. The tractor test reports can play an important role in the decision-making process. Both summary booklets and reports on individual tractors are useful for selecting tractor models or evaluating and comparing the performance of different tractor models.

The first step in the tractor selection process is to evaluate the needs that exist. Depending on the needs identified, the purchaser should estimate the power requirements at the PTO and drawbar. Knowing the power requirements, the next step is to identify tractor models that are capable of providing the required output power. This list may include tractors from different manufacturers if more than one dealership is in the vicinity.

Once the tractor models that meet the power requirements are identified, the next step in the selection process is to compare their performance data. This comparison can be accomplished by preparing a table similar to appendix A-2. The first column of this table may include the performance variables listed in appendix A-2, plus any other variables that are pertinent to the selection process. The number of additional columns will depend on the number of tractor models identified during initial screening. The data for each column can be extracted from the test reports. This table allows easy comparison among several tractor models.

The tractor information available in the summary reports may be used for the final selection. Factors such as stability, tire size, tractor configuration (two-wheel drive, front-wheel assist, four-wheel drive), repair frequency, proximity and reputation of dealership, and price may be considered in the final selection.

Table 1. Summary of tractors in the 70 hp to 80 hp (rated power-takeoff power) range.

Source: Data taken from the Nebraska and OECD Tractor Test Data for 2007 summary booklet (MP-37).

Notes:

¹ Chassis type: 2WD = two-wheel drive, FWA = front-wheel assist.

² Transmission: M = manual, PS = power shift, PQ = power quad.

³ Engine accessories: A = naturally aspirated, T = turbocharged, I = intercooled.

⁴ Specific fuel consumption, hp-hr./gal.

⁵ Drawbar test completed? NA = no data, PART = incomplete data, FULL = all data.

⁶ Sound test: first column is sound at operator’s ear, second column is 25 feet away (bystander).

⁷ Hydraulic flow in GPM, may be max flow from a single outlet; others may be from all ports.

⁸ Without a cab; otherwise the tractor is equipped with a cab.

To illustrate the step-by-step procedure for selecting a tractor using the Nebraska tractor test data, consider the following hypothetical example. Assume farmer Jeff Smith from Southwest Virginia is interested in selecting a new tractor for his orchard/vegetable operation. To select the tractor for this operation, follow the step-by-step procedure established earlier.

Step 1. Evaluate the need and estimate the power requirement. Jeff considered all the different operations that need to be carried out using the new tractor during the year. He estimated that the new tractor should have a minimum-rated PTO power of 70 horsepower.

Step 2. Identify all tractor models meeting the power requirement. A review of Nebraska and OECD Tractor Test Data for the 2007 summary booklet (publication MP-37) showed that 17 different tractor models meet the power requirement.

Step 3. Prepare a table to compare the performance data of tractors identified. Table 1 summarizes the performance data of the 17 tractor models identified from the summary booklet.

Final selection of a tractor model depends on many other factors, such as cost, personal preference, dealership location, safety features, fuel consumption, sound level readings, and hydraulic system capacity. For example, two service centers/dealerships (Case-IH and John Deere) are located within 20 miles of Jeff’s farm. If proximity of dealership is important to Jeff, the list is reduced to six models from Case-IH and John Deere. With the list narrowed to six tractor models, the final selection may be made taking the factors listed earlier into consideration.

Conclusions

The proper selection and sizing of a tractor is important to the economic viability and sustainability of farms in Virginia. This fact sheet introduces users to the Nebraska tractor tests and test reports. A step- by-step procedure for selecting a farm tractor using published tractor test reports has been developed and demonstrated.

Additional Resources

Five Strategies for Extending Machinery Life. Virginia Cooperative Extension publication 442-451.

‘Gear Up and Throttle Down’ to Save Fuel. Virginia Cooperative Extension publication 442-450.

Predicting Tractor Diesel Fuel Consumption. Virginia Cooperative Extension publication 442-073.

For tractor test information, contact:

Nebraska Tractor Test Laboratory
P.O. Box 830832
134 Splinter Labs
University of Nebraska-Lincoln, East Campus Lincoln, NE 68583-0832
Phone: 402-472-2442
Fax: 402-472-8367
http://tractortestlab.unl.edu
E-mail: tractortestlab@unl.edu

Acknowledgments

The authors acknowledge the contributions of John Perumpral, Gary Roberson, Robert Pitman, David Vaughan, and Roger Hoy to the previous version of this publication.

Appendix A-1. Nebraska tractor test summary booklet cover.

Appendix A-2. Nebraska tractor test summary booklet sample page 

Note: This summary shows three tractors from manufacturer New Holland.

Appendix B.1. Sample First Page From a Summary Tractor-Test Report 

Note: The top section shows the title box, the left-hand side shows the PTO-performance tests (top), the varying power tests (center), and the drawbar-performance test results (bottom). The column on the right has test conditions and tractor specifications.

Appendix B-2. Sample second page from a tractor test summary report.

Note: Includes extended drawbar-performance tests, sound-test results, and the tires and weight sections.

Appendix B-3. Sample Third Page From a Summary Tractor Test Report 

Note: Includes the three-point hitch performance section and hitch dimensions section.