Excerpts from the 1998 book "Aerodynamics of road vehicles":
The front half of a streamlined shape has a minor effect on its
drag.
A shape that had a Cd of .25 and 4" ground clearance would have a .26
Cd if it was 2 1/2" off the ground and .35 Cd if it only had 3/8" clearance .
If the nose of a car is on or below center the drag will be the same
and the low nose has down force - If the nose is above center it will cause
lift and have more drag .
Very little air getting under the car causes lift , a little more
clearance gives down force and if there's more air getting under , it causes
neither .
The lower the Cd the lower the wind noise .
A streamlined shape will have the least drag if the largest cross
section in the middle and if the length is 6 times the diameter - The drag is
only a little higher if the length is 8 or 9 times the diameter .
Bulges like in a hood , if shaped well cause very little drag .
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