With an ever-growing world population, the agricultural industry must continue to increase its efficiency whenever possible. Large amounts of energy are lost between the soil-tire interface, which can lead to an increase in slip and a decrease in energy efficiency. The Brixius equations are a set of equations designed to predict tractive performance. These equations were developed based on data acquired in the 1970's and 1980's, may not accurately represent today's tire and tractor technology nor accurately scale across a range of inflation pressures.

With a tractor fitted with instrumentation; the ability of the Brixius equations to predict the net tractive performance was analyzed across changes in tire pressure, soil condition, and ballasting. The actual drawbar pull produced by the tractor was measured by a load cell, while the deflection of the tire was found by ultrasonic distance sensors mounted inside the rim of the driving tires. A separate tractor was used to load the test tractor, which followed the methods of Zoz and Grisso (2003). After analyzing the data collected, it was determined that the Brixius equations were not able to fully account for changes in tire pressure when predicting net tractive force. Similarly, changes in soil conditions were also not completely captured by the Brixius equation. When using low tire pressure, a higher drawbar pull was produced by the tractor than anticipated with the model.