In the 49th annual Daytona 500 Sunday, NASCAR fans will see some of the most high-tech, finely tuned aerodynamics at work anywhere on or off the planet.
Aerodynamics has always been important to racing. But it has become more crucial as cars have become faster, given that drag caused by air friction is proportional to the square of the speed (which means the faster you go, the more the air works against you).
NASCAR rules do not allow a car's shape to be streamlined by much. Still, engineers will alter the body a quarter-inch here, a smidgeon there, to get a slight advantage. The Car of Tomorrow, NASCAR's new body type being used in some races this year, will limit a lot of this aerodynamic tinkering. But teams will still go to the wind tunnels to test tiny alterations.
"Aerodynamics will continue to be a major player at any place where the cars are going over 150 mph," said John Fernandez, managing director of the NASCAR operation for Chip Ganassi Racing with Felix Sabates, which owns three cars in the Nextel Cup series.
The three D's of racing
Certain courses require more attention to aerodynamics than others. The super speedways at Daytona and Talladega are long, fast tracks where cars get up close to 200 mph. Daytona is 2.5 miles long, with the backstretch a whopping 3,000 feet without a turn. This is where aerodynamics—both in the shop and on the track—becomes one of the many keys to winning.
"If a car at Talladega suffers damage to the body, it can just kill that team's chances," said Jerre Hill from University of North Carolina Charlotte's motorsports and automotive engineering program.
Engineers carefully design their car's bodies to reduce drag and to increase the aerodynamic "downforce" that helps the tires stick to the ground in a turn. And during a race, drivers draft behind each other to experience less wind.
These three aerodynamic elements: drag, downforce and drafting, are not separate [graphic]. Increasing downforce means more drag, while cars with a lot of downforce are not as good to draft behind.
Drag
Drag is commonly divided into two kinds: friction drag—due the wind breaking over the car's surface, and pressure drag—coming from the low-pressure wake that develops behind a car and sucks it backwards.
Teams make tiny tweaks to the body shape to make the air flow more smoothly, thereby reducing both friction and pressure drag.
But "there's not a whole lot of wiggle room," said Gary Eaker, whose Aerodyn Wind Tunnel in Mooresville, NC, runs tests for NASCAR teams 24 hours a day, 7 days a week.
"Teams have to become more and more creative," Eaker told LiveScience, just to get a half percent or so reduction in drag. But they are willing to do it because it can help them get a better qualifying position.
Downforce
Reducing drag is often secondary to increasing downforce, which allows cars to go faster through the turns.
"Drivers always say they need more downforce," Eaker said.
Downforce is also called "negative lift" because the physics is basically the same as the lift on an airplane wing, except it is turned upside down.
The average downforce on a stock car is between 1,650 and 1,750 pounds, Fernandez said. With this air-induced weight, tires have a tighter grip on the road, allowing drivers to maintain high speeds through the turns at Daytona and Talladega. But the drawback is that downforce adds to the drag.
"If you had your druthers, you'd have maximum downforce in the corners but little downforce on the straightaway," Fernandez said in a telephone interview.
Downforce can't be throttled back and forth like that. In fact, NASCAR teams are barred from changing the shapes of their cars during a race.
One way they get around this is by adding tape to the front grill. This increases downforce on the front of the car by causing more air to flow over the hood. But it also diverts air away from the radiator, so too much tape can cause a car to overheat.
Drafting
On the racetrack, both drag and downforce are affected by the air flow off nearby cars. In a common drafting situation, a lead car blocks much of the incoming wind, reducing the friction drag for a trailing car.
Drafting is important in many other sports, like bicycling. Roughly 90 percent of biking power is used to overcome drag, Hill said, so bike racers often ride in a pack, which can go 20-30 percent faster than a single rider.
Drafting bikers take turns in the lead position to block the wind for the others, so each can pedal furiously while at the front while relaxing somewhat when back in the pack. In car drafting, the lead car is also getting a benefit. Trailing cars fill in the lead car's low-pressure wake, thereby cutting down pressure drag. "The decrease in work for the lead car is substantial," Hill said.
With less drag for everybody, drafting lines can go about 5 mph faster than a single car. "On the super speedways you really need a drafting partner to get to the front," Fernandez said.
For Indy and Formula One racing, drafting is less effective. These open-wheel cars generate a huge amount of downforce, resulting in "giant-rooster-tail wakes that are less conducive to drafting," Hill said.
Car of Tomorrow
This year NASCAR will start using the Car of Tomorrow in certain races. The new design is primarily meant to improve safety, but it will also change the way that air flows over the car.
"It's a boxier car, so it has more drag," Hill said.
Two new components will be the main aerodynamic "knobs": a rear wing (replacing the spoiler) and a front splitter (a thin sheet under the front bumper that provides most of the front downforce).
Teams will be allowed to adjust the angle of attack on the wing and the position of the front splitter, Fernandez said.
"Everybody is going to be on a steep learning curve," he said.
The rest of the body shape will be more standardized, but Eaker doesn't believe this will hurt his wind tunnel business.
"It doesn't mean teams won't be changing things, it just means they will be nibbling off smaller and smaller effects," Eaker said.
