Dr. Diandra: What makes reconfigured, repaved Atlanta a Superspeedway?

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Atlanta Motor Speedway got a 163-day facelift during the off-season. Its corners were taken in a bit, its frontstretch was stretched and it had a banking augmentation. The 1.5-mile track that used to be teased as ‘cookie cutter’ (even though it really wasn’t) is the first high-banked 1.5-mile oval in NASCAR.

And it’s expected to race like a superspeedway.

Why Make Atlanta a Superspeedway?

A few years ago, the track’s deteriorating surface condition hinted that a repave would be unavoidable. That opened the door for discussions about what changes made sense. Steve Swift, senior vice president of operations and development at Speedway Motorsports, oversaw Atlanta’s reconfiguration.

“Uniqueness,” Swift said, “isn’t enough. What do we have as a company? What does the sport need?”

Speedway Motorsports already had four other 1.5-mile tracks: Charlotte, Kentucky, Las Vegas and Texas, as well as shorter ovals and road courses. What they didn’t have was a superspeedway like Daytona or Talladega.

“No one’s ever made a 1.5-mile oval with banking substantially over 24 degrees before,” Swift noted.

Reconfiguring a track, especially one as beloved by drivers at Atlanta, is a risky proposition, and that’s before attempting to do something brand new to NASCAR. Ten months of computer simulations helped mitigate that risk.

“iRacing offered to help,” Swift says. “The great part is that you can change things prior to spending a lot of money and putting it out there.”

The simulations confirmed Speedway Motorsports’ goals for the new Atlanta.

“We ran the numbers, and the track we had designed replicated superspeedway racing,” Swift said.

Power and Drag

Nick Fishbein, head of GM Racing’s Performance Engineering Group, draws the threshold for a ‘superspeedway’ using what engineers call the power-drag relationship. If you’re one of the people who had to learn Newton’s Laws of Motion in school and thought ‘When will I ever use this?’ The answer is: right now.

Newton’s first law says that you can’t accelerate a car without a force. The second law says that the acceleration is proportional to the net force acting on the car. More net force means more acceleration. Net force means the sum of all forces acting on the car, just as net profit is the difference between the selling price and the cost of making whatever you sold.

The force created by the engine isn’t the only force acting on the car. There’s also drag, caused by air molecules not wanting to get out of the car’s way. It’s easier to picture drag in water because you can see water. When you move in a pool, you have to push the water out of your way. Cars do the same thing with air molecules. Although each air molecule is really small, there are a lot of them.

That leaves the race car in a tug-of-war between the force from the engine pushing it forward (to the left in my diagram) and the drag force pulling backward.

A block graphic showing the forces acting on a racecar
The car is moving to the left in this diagram

This leaves us with three possibilities.  

  • If the engine exerts more force than the drag, the car accelerates.
  • Less engine force than the drag means the car slows down.
  • If the engine exerts the same amount of force as the drag, the car travels at a constant speed, meaning it neither accelerates or decelerates.

The Catch

NASCAR rules limit engine horsepower, but drag answers only to the rules of physics. Drag increases with the square of the car’s speed, which means that a race car going 180 mph experiences four times the drag as the same car going 90 mph.

  • If you go twice as fast, the drag gets four times bigger.
  • If you go three times as fast, the drag is nine times larger.

At most tracks, a race car’s engine power is more than enough to overcome drag. Superspeedways offer the potential for speeds high enough to allow cars to go airborne. To prevent this, NASCAR limits horsepower at superspeedways even more than at other tracks, and these engines can’t provide enough force to beat the drag force. The cars reach terminal velocity: They simply can’t go any faster. This is why drivers can hold the throttle open all around a superspeedway.

Teams go to extremes to minimize drag because even a little less drag produces a little higher terminal velocity. This physics is also why drafting is the only way to go faster on a superspeedway: Forcing the air to flow uninterrupted over two cars cuts the drag force for both. Because of the speed and rules package, that’s what we expect to see at Atlanta.

“The emphasis on aero versus setup versus strategy depends on the track,” Fishbein explained. “Atlanta won’t be grip limited.”

That means factors teams typically focus on at 1.5-mile tracks, like tire fall off, won’t come into play at Atlanta.

“You’re forced into a small corner of optimizing the setup region,” Fishbein said.

Because NASCAR’s rules leave little room to change aerodynamics, they’ll focus more on pit strategy and how to call the race.

The View From the Tires

Goodyear organizes NASCAR tracks into seven ‘venue groupings’ based on the loads and wear the tire must sustain. Last year, Atlanta was grouped with other 1.5-mile tracks. This year, Atlanta is in with the superspeedways. But that grouping doesn’t mean Atlanta is just like Daytona and Talladega.

“Atlanta is unique,” Greg Stucker, Goodyear’s director of race tire sales said. “It’s got 28 degrees of banking, new asphalt, and tighter corners than Daytona and Talladega. But we group Atlanta with the superspeedways because it’s using the same rules package.”

The tires don’t really care if the racing is pack, pod, or regular, but on a new, fast track like Atlanta, Stucker says, “tires still don’t trump the importance of the draft. Look at Daytona. Tires have much less of an impact than at other places.”

While that will likely be the case this weekend in Atlanta, tracks constantly change.

“As a racetrack ages,” Stucker notes, “the tires start to make a difference. The longer since the Daytona repave, the more difference tires make.”

There’s no reason to believe the same won’t hold true for NASCAR’s newest superspeedway.