Aerodynamic measurements for vocational vehicles.

This section describes an optional methodology for determining improved aerodynamic drag area, C d A , for vocational vehicles, as described in § 1037.520(m), rather than using the assigned values. A vocational vehicle's aerodynamic performance is based on a D C d A value relative to a baseline vehicle. Determine a D d A value by performing A to B testing as follows: (a) Use any of the procedures described in this subpart, with appropriate adjustments, for calculating drag area. (b) Determine a baseline C d A value for a vehicle representing a production configuration without the aerodynamic improvement. Repeat this testing and measure C d A for a vehicle with the improved aerodynamic design. (c) Use good engineering judgment to perform paired tests that accurately demonstrate the reduction in aerodynamic drag associated with the improved design. (d) Measure C d A in m 2 to two decimal places. Calculate D d A by subtracting the drag area for the test vehicle from the drag area for the baseline vehicle. [89 FR 29783, Apr. 22, 2024]