The basics of airflow around...
The basics of airflow around the wheelwells and a low air dam are the same on oval track stock cars as well as those designed for road courses. Photo by Jerry F. Boone
Manufacturers spend far more time in the wind tunnel developing their newest street cars than any of the Nextel Cup teams devote to smoothing the contours of their latest oval track racer.
They move the nose up and down, smooth the seams, and massage the body contours. They nip a bit here and tuck a tad there in pursuit of a body shape that will move a Fusion, Charger, or Monte Carlo through the air with the least resistance.
Automakers know that an aerodynamically clean car requires less horsepower to move down the highway than one with a body that looks like it was developed in the shipping department.
This is all part of the effort to make today's vehicles fuel efficient, but we know that aerodynamics also works for racers.
Given the same horsepower, a car with a shape that can use the air will go down the straight faster and corner better than one with fenders flapping in the breeze and a nose that looks like it kissed a bulldozer blade.
The Nextel Cup CAT car is...
The Nextel Cup CAT car is a template for everything you need to know about effective race car aerodynamics. The air dam sweeps as forward as the rules allow, the fenders flare out in front of the tire and tuck in behind it, the shape of the window post deflects air away from the inside of the car, and the flat deck helps spill air onto the rear spoiler. Photo by Jerry F. Boone
That's only important for Nextel Cup cars, you may be thinking. Amateurs never go fast enough on a short track for aerodynamics to be an issue. But here's a simple test that will prove you wrong.
The next time you drive to the parts store for another box of horsepower, stick your arm out the window at 50 mph. Rock your hand back and forth and feel how the wind moves it up and down.
Then consider that 50 mph is far slower than cornering speeds at almost any short track in the country.Still think aero doesn't make any difference on a short track?
Back in the heyday of NASCAR's more recent aero wars (we aren't talking about the wings 'n things era of the Superbirds) about six years ago, a Winston Cup car could make in excess of 2,200 pounds of downforce at 200 mph. The figures were derived from results of wind tunnel testing on a moving plane platform.
Downforce and speed aren't purely linear. When you double the speed, the downforce goes up four times. Working the figures in reverse, we can determine that at 100 mph, a decently developed stock car can develop roughly 500 pounds of downforce.
How close you come to hitting those numbers depends largely on what you have to work with and how much you do to it. The results will vary with the type of chassis and body on your car, the class you run in, how strict the rule book is as well as how closely it is followed by the tech inspectors.
Aerodynamic principles work...
Aerodynamic principles work the same no matter if the air is flowing over a clay oval or a pavement oval. Good aero management to the rear spoiler is critical on a dirt track car because it spends so much time sideways. Photo by Jerry F. Boone
We consulted with . . . well, we can't tell you who we consulted with because he's not supposed to talk to the media on this subject. We can say he's an industry and racing insider who has worked with teams ranging from local short track racers to NASCAR's top levels, has designed and produced his own race cars, and even today is involved in vehicle development. His advice and opinion is respected and welcomed in any Nextel Cup garage.
We'll call him "Mister Breeze," acknowledging that on race cars, he knows which way the wind blows.
Anyone can slap together a stock car and make 300 or 400 pounds of downforce, he says. It is just the nature of the air moving over the car. The difference between guys who just race through the air and those who use it to their advantage is in the details.
"To begin with, the air behaves the same whether it is moving over a Nextel Cup car or a local Street Stock," he says. "So guys who are running on local short tracks can learn a lot by just looking closely at a Nextel Cup or Busch car and seeing how those teams do things.
"There is a reason for everything they do on the body. Nothing is left to accident.
There is nothing on the side...
There is nothing on the side of a Nextel Cup car that disturbs the airflow. Photo by June Boone
"So, let's begin where the air begins-at the nose.
Set the air dam as far out front as you can, he says. Move it out as far as the rules allow, or as far as you can get away with in tech inspection. In a perfect world, the bottom should extend at least a couple of inches beyond the rest of the nose sheetmetal.
"It should look like a cow catcher on an old time train," he says. "Then, get the bottom as close to the track as you can. On something like a half-mile oval, you aren't concerned about downforce on the straights. What you want is as much as possible in the corners, because that's where you spend most of your time.
"The air dam does two things. It helps push the nose of the car down when the air presses against it, but it also prevents the air from getting underneath the car."
Blocking the air from beneath the car creates a low-pressure area under the nose. The vacuum helps keep the nose planted in the corners. It doesn't matter if the downforce is created by the air pressing the nose down from above, or if the car is being sucked down from beneath. The end result is more stick in the corners.
The long, flat decklids of...
The long, flat decklids of these composite-bodied cars help push more air onto the spoiler and build rear downforce. Photo by Jerry F. Boone
"In some ways short track racers have it better than the Cup teams," Breeze says. "The tires they use generally are far stickier than what goes on a Cup car. A lot of them can hold a 1.5 g-load. That means that if you can hit 500 pounds of downforce, it's like having 750 on tap. Those are big numbers on a short track."
From here, things get a bit more complicated, especially if you run a series that uses templates or if you have a Street Stock on a unibody.
"Move the nose to the right," Breeze says. And then do the same thing to the rear.
It may take some creative sheetmetal work and a visit to a friend's body shop, but there is an advantage to be gained by making the right side of the car a bit concave (like the inside of the letter "C").
"In 'Cupland,' the term is 'showing the spoiler,'" he says. But it is a lot more complicated than that.
While the right side should be concave, make the center of the left side as fat as possible, he says.