The ideal nose for creating...
The ideal nose for creating downforce in a stock car would be narrow at the front with flat sides that are angled out beyond the tires. The radiator box intake would be wide and low to prevent the air entering under the nose from mixing with the low-pressure air under the hood. The nose on our LMS car has all of those features.
The shape of the front nosepiece can help determine how much air is directed under the car and how much moves up and over the hood. Obviously, the more air that passes over the top, the less air that will invade the low-pressure area under the hood.
Vertically flat noses tend to build a pressure front that pushes the air in all directions and disturbs the orderly flow of air. This will force more air under the nose as well as disturb the free flow of air around the side of the car and past the wheelwell. The suction effect that produces the low pressure is less effective, and the car will have less frontal downforce.
If the nose were angled with the lower edge farther forward, the oncoming air would be cut more cleanly and would not build up into a pressure front. Less air would flow under the nose, and the flow of air around the sides of the nose would be cleaner, with less turbulence.
The overall balance of the setup in the car has an effect on downforce. A car that is set up so that the rear suspension is rolling more than the front will cause the car's left-front area to rise. This allows more air to flow under the car and replace the low-pressure air, which results in less downforce effect.
In a NASCAR Cup test I was involved in at Daytona in early 1996, a team rearranged their spring rates so that as the car negotiated the turns, the left front traveled more. The left-front shock travel increased over an inch, and the car picked up an honest 3 mph.
Short-track teams are now using larger sway bars and softer springs so that body roll is reduced and the front end is more compressed into the racetrack to eliminate much of the airflow under the nose. These cars turn better due to the increased downforce this creates.
A flat nose will create a...
A flat nose will create a pressure front much like a bubble. This impedes the air trying to flow over and around the car and causes turbulence. More air is forced under the nose of the car, and the air that is flowing around the sides will be disturbed.
A slightly angled nose tends...
A slightly angled nose tends to cut the air more cleanly, and more is directed up and around the nose with a smoother flow.
Rear spoiler angle will produce...
Rear spoiler angle will produce both downforce and drag. The greater the angle from horizontal, the more drag and less downforce created.
Major-league teams use wind tunnels to perfect the aero efficiencies for both downforce and drag. Each session may be split to include a short/medium-track car and a superspeedway car because the goals for each are different.
In the wind tunnel, the attitude of the car is adjusted to simulate the way the car dives and rolls as it circles the racetrack. There is also a feature at some tunnels that will yaw the car, or rotate it as if it were on a round table. The latest technology utilizes a moving platform under the car to better simulate a real race car driving into the wind.
A very low angle on the spoiler...
A very low angle on the spoiler offers less drag, but also very little downforce. The optimum angle found during wind tunnel testing is around 55 degrees.
The key goals with stock car aero design and testing is to create a body shape and inner construction that will provide more downforce to enhance turn speeds, produce less drag, and promote a more balanced race car.
If we work hard to develop 600 pounds of downforce on the front end and the rear is not able to keep up with that high amount of grip, then the car will be loose-nobody can drive a loose car fast. So there are limits to how far we can go. It is also possible to create so much front downforce that the car is undriveable.
Work toward a good balance of front-to-rear aero downforce to help produce more overall grip. Do not overdo your efforts to help the car aerodynamically at the expense of handling efficiency. Make sure the basic chassis setup is balanced, and then the combination of both aero downforce and handling will enhance your on-track performance.
Many short track teams gain more aero downforce by utilizing the big bar and soft spring (BBSS) setups. This produces a very low and square nose attitude in the turns, helping to reduce atmospheric pressure under the body.