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This SAE J2971 Recommended Practice describes a standard naming convention of aerodynamic devices and technologies used to control aerodynamic forces on truck and buses weighing more than 10000 pounds (including trailers).

This SAE J2971 Recommended Practice Truck and Bus Aerodynamic Device Terminology document describes a standard naming convention of aerodynamic devices and technologies used to control aerodynamic forces on truck and buses weighing more than 10,000 pounds (including trailers).

This procedure incorporates test cycles that produce relative fuel economy data relating to long haul, short haul, and local driving patterns, or any combination of these and to those components developed to improve fuel economy for these patterns. The tests conducted on a specific vehicle are to reflect that vehicle's general mode of operation. The procedure is intended to be used under controlled, warmed-up conditions on a test tract or on suitable roads. A minimum of two vehicles running simultaneously is required. Test condition recommendations are provided for undertaking this engineering test. If it is necessary to conduct a test outside of these test conditions, the purpose of the test and the variant conditions should be recorded and noted whenever the results are reported.

This recommended practice provides minimum requirements for testing components or systems of the type which can be switched from one truck to another with relative ease; i.e., aerodynamic devices, clutch fans, radial tires, and the like. The test utilizes in-service fleet vehicles, operated over representative routes. The relative fuel effectiveness of the component or system under test is determined as a percentage improvement factor. This factor is calculated using the relative fuel usage of like vehicles operating with and without the specific component or system under evaluation. Accuracy capability employing this test technique is either ±1% or ±2%, depending upon the method of fuel measured. (See paragraph 7.4.)

The testing technique outlined in this recommended practice was developed as part of an overall program for testing and evaluating fuel consumption of heavy-duty trucks and buses. The technique outlined in this recommended practice provides a general description of the type of equipment and facility which is necessary to determine the power consumption of these engine-driven components. It is recommended that the specific operating condition suggested throughout the test be carefully reviewed on the basis of actual data obtained on the specific vehicle operation. This recommended practice covers evaluation techniques for determining the power consumption characteristics of hydraulic pumps used on heavy-duty trucks and buses.

This document describes a rigorous engineering test procedure that utilizes industry-accepted data collection and statistical analysis methods to determine the road load and to estimate the aerodynamic drag area of trucks and buses weighing more than 10000 pounds. The test procedure may be conducted on a test track or on a public road under controlled conditions and supported by extensive data collection and data analysis constraints. The estimated aerodynamic-drag-area result represents a single-speed and single-yaw-angle condition. Test results that do not rigorously follow the method described herein shall not be represented as an SAE J2978 result.

The testing techniques outlined in this SAE Recommended Practice were developed as part of an overall program tor testing and evaluating fuel consumption of heavy duty trucks and buses. The technique outlined in this document provides a general description of the type of equipment and facility which is necessary to determine the power consumption of these engine-driven components. It is recommended that the specific operating conditions suggested throughout the test be carefully reviewed on the basis of actual data obtained on the specific vehicle operation. If specific vehicle application is not known, see SAE J1343.