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
C
d
A value relative to a baseline vehicle. Determine a
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
A by subtracting the drag area for the test vehicle from the drag area for the baseline vehicle.
[89 FR 29783, Apr. 22, 2024]
