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It's been several years since I had my CFD course, so the details are all now a bit fuzzy. I would still argue that lowering any car an inch, by itself, does not improve the overall Cd for that car. In most cases removing the mirrors will drop as much Fd as lowering a car by an inch.

This infers a reduction in area, not a change in Cd. Could there be some loss of turbulance from masking the tires as well as reducing the frontal area, perhaps. The largest gain is the reduction of frontal area from masking the tires. A far larger drop in drag can be gained by the placement of deflectors upstream of the rear tires and the use of an air dam and sideskirts.

The rear diffuser does not speed up airflow. A properly designed diffuser slows down air flow. The trick is keeping the flow attached while you increase flow area and increase pressure. You want to fill the rear void with equal pressure to the surroundings. This eliminates the turbulance and drag from the collapsing slipstreams off an abrupt rear end.

This does not happen for free. There is still drag created, but less overall than the abrupt disruption.

<blockquote data-quote="Ty B" data-source="post: 1387786" data-attributes="member: 22809">It&#039;s been several years since I had my CFD course, so the details are all now a bit fuzzy.&nbsp; I would still argue that lowering any car an inch, by itself, does not improve the overall Cd for that car.&nbsp; In most cases removing the mirrors will drop as much Fd as lowering a car by an inch.&nbsp;This infers a reduction in area, not a change in Cd.&nbsp; Could there be some loss of turbulance from masking the tires as well as reducing the frontal area, perhaps.&nbsp; The largest gain is the reduction of frontal area from masking the tires.&nbsp; A far larger drop in drag can be gained by the placement of deflectors upstream of the rear tires and the use of an air dam and sideskirts.&nbsp;The rear diffuser does not speed up airflow.&nbsp; A properly designed diffuser slows down air flow.&nbsp; The trick is keeping the flow attached while you increase flow area and increase pressure.&nbsp; You want to fill the rear void with equal pressure to the surroundings.&nbsp; This eliminates the turbulance and drag from the collapsing slipstreams off an abrupt rear end.&nbsp;This does not happen for free.&nbsp; There is still drag created, but less overall than the abrupt disruption.</blockquote>

[QUOTE="Ty B, post: 1387786, member: 22809"] It's been several years since I had my CFD course, so the details are all now a bit fuzzy. I would still argue that lowering any car an inch, by itself, does not improve the overall Cd for that car. In most cases removing the mirrors will drop as much Fd as lowering a car by an inch. This infers a reduction in area, not a change in Cd. Could there be some loss of turbulance from masking the tires as well as reducing the frontal area, perhaps. The largest gain is the reduction of frontal area from masking the tires. A far larger drop in drag can be gained by the placement of deflectors upstream of the rear tires and the use of an air dam and sideskirts. The rear diffuser does not speed up airflow. A properly designed diffuser slows down air flow. The trick is keeping the flow attached while you increase flow area and increase pressure. You want to fill the rear void with equal pressure to the surroundings. This eliminates the turbulance and drag from the collapsing slipstreams off an abrupt rear end. This does not happen for free. There is still drag created, but less overall than the abrupt disruption. [/QUOTE]

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