1) Decades-old mirrors would ( have been reported at ) delta-Cd 0.015. Giving you Cd 0.225.
2) TESLA-quality mirrors would be delta-Cd 0.010, giving you Cd 0.23.
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' With a long diffuser, a notable reduction in drag can be achieved with a very small angle... However, this effect is only assured with a very smooth underside.' Dr.-Ing. Wolf Heinrich Hucho, 2nd-Edition, page-144
3) No belly-pan, no diffuser, and lose 30-counts.
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Belly pan with diffuser, rear skirts, and mirror delete: Cd 0.19-to- Cd 0.195.
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The 2012 Coventry University testing of the Audi A2 box-cavity showed a 2% delta Cd, from a car with Cd 0.288.
2% from a Cd 0.24 car would be 0.0048, yielding Cd 0.1852-to- Cd 0.1902
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I taped all the seams on SPIRIT and it showed zero difference in the wind tunnel. General Motors allowed 0.007 for these 'features'.
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' Qualitatively, the effect of the length upon the aerodynamic drag is similar to that for the ( streamline ) body of rotation.' W.H. Hucho, 2nd-Ed., pg 142
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' the drag reduction from an elongated tail varies almost linearly with the reduction in cross section area.' Jeff Howell et al.,' Streamlined Tails- The Effects of Truncation on Aerodynamic Drag,' Loughborough University, 2020, Abstract, SAE Paper 2020-01-0673
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' base pressure also depends upon the angle at which the flow separates from the contour.' W.H. Hucho, 2nd-Ed, page- 141