Imroving Fuel Economy
Your car will provide improved fuel economy with a few simple modifications learned from the masters of vehicle aerodynamic improvement - racers. While the aerodynamic shape of most types of racing cars is a result of compromising numerous factors including drag, downforce, stability cooling, appearance and the like, there are a few forms of automotive competition which epmhasize the reduction of aerodynamic drag more than the others.
Speed record cars are probably the epitome of attention to drag reduction. Studying the more stock-bodied classes of thse vehicles provides some solid direction for a few simple modifications. First, it is normally true that a vehicle with a slightly nose-down attitude will have a lower drag coefficient than one with a tail-down stance. A slight modification to the front or rear suspension, or a slightly smaller front tire size, will deliver that effect.
Moving to the front end - the air that flows under the front bumper/air dam normally causes a significant contribution to increased drag. The front air dams on most cars are shorter than they could be in the interest of not hitting curbs when parking, or not scraping when going down a ramp onto a street and conditions such as that. Adding a rubber extension to the existing front air dam will normally contribute to a reduction in aerodynamic drag for your vehicle with no negative implications other than those mentioned above.
Most rear spoilers have been designed for appearance, and contribute little in the way of aerodynamic effect. Aside from added weight it is most likely that if they are working to add downforce thay are also adding drag and harming fuel economy.
The other type of race car which has a greater emphasis on drag reduction is the endurance racer (like LeMans, Sebring, etc). Studying photos of these cars, especially those based on stock-bodied production cars, will provide many directional hints for ways to subtly modify your street car to reduce drag. It is always important to remember that these cars are tuned aerodynamically to both reduce dra and increase downforce. A Formula 1 car will have a many times higher drag coefficient than your street car, even hough it goes 230 mph or more.
Aerodynamics, cornering performance and appearance are factors, as well as needed openings for cooling of engines, brakes and other areas. Still, there are ways to improve fuel economy without hurting the other areas of functionality in your street car.
