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A rounded nose that gradually widens will help maintain the laminar boundary layer. The laminar boundary layer will
Reducing the surface area will decrease drag, but may not be feasible due to neading surface area for a solar panel
A smooth surface is the most important factor in keeping a a laminar boundary layer.
A thinner body is desirable as well, because the reduced stagnation pressure at the rear of the car, and therefore the resultant pressure difference between front and back, will be acting on a larger area for a wider car.