The Director


Roger M. Hoy

The Nebraska Tractor Test Laboratory 100 years and counting adapted from Resource Magazine May/June 2020

The Nebraska Tractor Test Laboratory (NTTL) began with a farmer who purchased a tractor that did not perform as advertised. In 1916, Wilmot Crozier, of Osceola, Nebraska, bought a Minneapolis Ford Model B. He found this tractor to be unreliable and had trouble getting parts and maintenance; no such services were available in Nebraska. In 1919, Crozier was elected to the State Legislature, where he teamed up with Nebraska Senator Charles Warner to write the Nebraska Tractor Test Law. They were aided by L. W. Chase, chair of the Agricultural Engineering Department at the University of Nebraska. The bill passed easily and was enacted into law in 1919.

The original Tractor Test Law contained several provisions that remain largely unchanged: The Agricultural Engineering Department (now Biological Systems Engineering) is responsible for testing advertised claims; at least one tractor parts warehouse and one repair facility are required in Nebraska; permits to sell tractors are issued by the State Railway Commission (now the Department of Agriculture); a board of engineers, under control of the University, develops the test procedures and reviews all test results.

Shortly after, NTTL was established. A building was constructed and equipped with the necessary tools and office space; an outdoor test track was built. Professor Chase convinced Claude Shedd, a former student, to serve as the first Engineer-in Charge. As required by the law, a board of engineers was established from department faculty to approve the test procedures. The first tractor test, involving a John Deere Waterloo Boy Model N, was completed on April 9, 1920.

In the early years, tractor testing consisted of validating the manufacturer’s claims for drawbar horsepower and belt horsepower. Fuel consumption was also measured. For belt horsepower measurements, the flat belt drive on the tractor was connected to an electric resistance dynamometer, which provided the load. For drawbar testing, a load car was built by adding a traction dynamometer to a tractor frame that was pulled in reverse. This load car was attached to the drawbar of the test tractor using a hydraulic cylinder with an internal spring. As the spring was compressed by the pull of the tractor, the increased hydraulic pressure was measured with a pressure gauge.

During the 1920s, various load cars and load units were developed for drawbar testing, and many changes in tractor testing have occurred due to changes in tractor technology. Measuring drawbar pull using the pressure in a hydraulic cylinder was an excellent early choice; this test method was used until 2011.

The Tractor Test Law had the intended effect of eliminating disreputable tractor manufacturers. Even outside of Nebraska, where the law did not apply, lack of successful NTTL testing became a barrier to sales. Further, the Great Depression caused consolidation, and elimination, of many tractor manufacturers, resulting in fewer tractor models. A major change occurred in 1934, when the first rubber-tired tractor, the Allis Chalmers WC, was introduced. For the next several years, the NTTL often tested the same model on both steel wheels and rubber tires. By 1937, the last of the steel-wheeled tractors was tested. A new load car, designed by Charlie Adams, was implemented in 1938 and remained in use until 2003, although it was extensively modified over time. The Adams load car was equipped with precision pressure gauges for the hydraulic cylinders, among other features.

With the advent of World War II, the NTTL discontinued operations because tractor manufacturers converted to war production. Carlton Zink, one of the NTTL’s long-serving Chief Engineers, spent the first two years of the war teaching farmers how to keep their equipment running. He left the NTTL in 1943 to work for Firestone and then Deere, where he retired in 1968. At Deere, Zink pioneered the development of rollover protective structures (ROPS) for agricultural tractors.

In 1946, operations resumed with Engineer-in-Charge Lester Larsen, who led the NTTL until 1976, a period that saw much tractor development. In 1956, a change was made to the Nebraska Tractor Test Law to refine the definition of a tractor, which created a more modern definition of an agricultural tractor. Although steel-wheeled tractors were once widely used, by 1956 all agricultural tractors ran on rubber tires. NTTL constructed a new concrete test track that required less maintenance than the original cinder track and provided more consistent testing conditions. By 1960, the Adams load car required significant modifications to handle the higher horsepower tractors that were becoming available. The modifications allowed the load car to handle up to 10,000 lbs. of drawbar pull, which could be further increased with the use of load units. This final load car configuration, developed by John Carlisle, still exists and is on display at the Larsen Tractor Test and Power Museum.

The NTTL has always solicited opinions from farmers and manufacturers to improve the tractor tests. In the late1960s, farmers suggested adding noise measurement to help them select quieter tractors. Instituted in 1971, the noise testing procedure was developed by Ned Meier as part of his MS project. As soon as the noise results began to appear in NTTL reports, manufacturers began to compete to produce quieter tractors.

In Europe, the OECD Tractor Test Codes were established in 1957, when the OECD developed tests to validate ROPS designs. During Lester Larsen’s tenure as Chief Engineer, the NTTL collaborated with the OECD to furnish the information needed for tractor performance tests. The OECD published its first tractor performance code in1973. Globalization began to play a larger role.

By the 1980s, cost-cutting efforts by manufacturers resulted in pressure on the NTTL to accept performance tests conducted at OECD test stations, rather than requiring that tractors be tested at both the NTTL (to meet the Nebraska law) and at OECD test stations (to meet European requirements). In 1986, the Tractor Test Law was changed to recognize testing at OECD test stations. Simultaneous to this change, the U.S. formally adopted the OECD Tractor Test Codes. The NTTL was appointed as the official review agency for OECD tractor testing. This designation allowed the NTTL to submit and approve OECD test reports.

As it happens, the OECD Code 2 performance test is essentially the NTTL’s testing procedure. The OECD also supports protective structure testing of tractors for ROPS and falling object protection. While protective structure testing is not conducted at the NTTL, NTTL engineers typically direct 25 to 35 protective structure tests each year.

In 1984, hydraulic lift testing was added to the testing procedures, and in 1988, the NTTL began measuring and documenting the hydraulic power of tractors. Larger tractors created challenges. A new lab was built with doors 24 ft wide to accommodate larger machines; but, the concrete test track was only 15 ft wide and it was occasionally necessary to perform tractor testing at Lincoln Airport, which had a paved surface wide enough for the largest tractors.

Recent changes have involved environmental regulations. In 1996, the EPA introduced Tier 1 emission standards for off-road compression ignition engines. Evolving emission standards caused new tractor models to be introduced every three to five years, greatly increasing the demand for tractor testing. This trend continued through 2017, when the last Tier 4b models were tested.

In 1998, the Engineer-in-Charge became known as the Director, and Leonard Bashford took on the role. Bashford was no stranger to the NTTL, having served many years as both a member and chair of the Nebraska Board of Tractor Test Engineers. A major change during Bashford’s tenure was the first significant upgrade of the load car since the 1960s.The new load car, acquired from Caterpillar, was based on an articulated dump truck chassis. A front yoke supported the hydraulic cylinders used to determine drawbar pull. A fifth wheel was added to determine the speed and distance traveled for calculating power and wheel slip.

Bashford retired in 2006, and I was induced to leave Deere and assume the role of NTTL Director. My first challenge was the concrete test track. The old track had been in use since 1956, and the surface was badly deteriorated. During the summer of 2007, the old track was replaced. The new track is longer, and the width has been increased from15 to 22 ft, so no more testing at Lincoln Airport! .

Current tractor performance tests are conducted according to OECD Code 2, which includes both mandatory and optional test procedures. An OECD test report requires only the mandatory procedures, which include PTO testing, hydraulic flow testing, three-point linkage testing, and draw-bar testing. Testing of tractors is further defined by decisions of the Nebraska Board of Tractor Test Engineers. Their decisions are communicated through Board Actions. Because the OECD only provides testing procedures, many Board Actions relate to verifying actual tractor performance. For example, Board Action No. 18 describes the evaluation of PTO and drawbar performance claims.

The use of electric power on tractors is a new challenge for the NTTL. In 2017, the NTTL evaluated two electric tractors manufactured by Solectrac designed for orchard and vineyard work. While the tractors were not officially tested, the evaluation provided useful information to both Solectrac and the NTTL. Another upcoming technology is the delivery of electric power directly to attached implements. This power may be produced by a flywheel generator or a diesel electric power train. When electric power is supplied to implements, it will become another available power source, just like hydraulic, PTO, and drawbar power.

Another challenge involves relating tractor tests to implement power requirements. Field implements typically consume tractor power through more than one power source. For example, an air seeder may use both drawbar power and hydraulic power. Measurement systems for drawbar, PTO, and hydraulic power can be deployed in the field to collect actual implement power requirements, while CANBUS data can be collected on engine speed and power. During official tractor testing, CANBUS data can then be collected for the same parameters, thereby establishing the efficiency of power transmission from the tractor’s engine to the various power outlets. The ability to correlate CANBUS data with actual power delivered during official testing will allow evaluation of tractor efficiency in the field, so farmers can select the bes ttractor for the intended use. We are working with researchers funded by the USDA to develop this new understanding of in-field power requirements.

Since the NTTL’s first test in 1920, tractor technology has changed enormously. The staying power of NTTL can be explained by our consistency in supplying accurate, unbiased, and relevant performance data. Without our reputation for integrity, we would not have survived. At the same time, if we had not adopted new testing procedures with the changes in tractor technology, we would not have survived.

As the NTTL begins its second century, those two qualities define our mission. The NTTL also serves a secondary mission in educating agricultural engineering and agricultural mechanization students. Each semester, up to 30 students are employed part-time and provide much of the labor required for tractor testing. Our students work with NTTL staff and with engineers from various manufacturers, gaining hands-on experience that is an excellent complement to their classroom studies. Today, former NTTL students are working at all levels of the equipment industry.

Modern agricultural tractors have evolved far beyond the early tractors that competed with horses. By 2120, they will be much evolved from today, and the NTTL will still be testing them.

Roger Hoy
Director, Nebraska Tractor Test Laboratory

ASABE Fellow