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Dr. Diandra: Dissecting Cup’s new short track package

Kim Coon, Nate Ryan and Kyle Petty explain how less down force gives the illusion of adding horse power to the car, and predict how this might impact the driving at Phoenix Raceway.

NASCAR will introduce a new short-track package for the Next Gen car this week at Phoenix Raceway. With 30% less downforce, the modifications are intended to improve the disappointing racing at some smaller tracks in 2022.

What’s changed in the new short track package

The most obvious change is the 2-inch spoiler, which is half the height of spoilers for other tracks. The short-track spoiler is also narrower, measuring 58 inches across compared to the 60-inch width used at other tracks.

But the most significant changes are under the car. The Next Gen car creates downforce with a smooth underbody that moves air out from under the car. The lower pressure sticks the car to the track.

The process is largely managed by a part of the underbody called the diffuser. I’ve outlined the diffuser in yellow in the photo below. I also labelled the diffuser skirts and the five strakes positioned between the skirts.

An annotated photo of a Camero from the rear, with the diffuser, strakes and skirts labelled

The next photo shows the full length of the diffuser. You can also see the bolts holding the pieces together. That modular design is largely why NASCAR was able to implement the new package so quickly.

A photo of the diffuser, showing the positions of the strakes and skirts

Photo Credit: Dustin Long

What’s a strake?

A strake, like a splitter or spoiler, is an aerodynamic appendage that forces air to travel over (or under) a car in a very specific way. Andrew McColgan, NASCAR aerodynamics specialist at Chevy’s Charlotte Technical Center, explained that a complete understanding requires invoking the subtleties of vortex dynamics.

So let’s try an analogy. Imagine a stadium or other facility that hosts large crowds. When an event ends, people want to leave as quickly as possible.

If the exit is a single large opening, people move toward it from all directions. They have to slow down or speed up to avoid running into each other. It’s basically a free-for-all.

A better idea is creating lanes that funnel everyone in the right direction. People exiting the stadium see the lanes and adjust their paths ahead of time. You can think of strakes in the same way. They create the fastest way for air molecules to get out from under the car.

The Next Gen’s new short track package removes the three interior strakes (indicated by red arrows in the photos) and shortens the diffuser skirts. That prevents air molecules from exiting the car’s underside of the car as quickly, which decreases downforce.

Despite its location in the rear of the car, the diffuser creates front and rear downforce. Keeping the car balanced required also removing the engine panel strakes, which are located further toward the front of the underbody.

Less downforce equals more driver input

Eric Jacuzzi, NASCAR vice president for vehicle performance, told SiriusXM Radio’s “The Morning Drive” that the new short track package provides about 30% less total downforce relative to the original package. Testing showed little decrease in straightaway speed, thanks to the lower drag from the smaller spoiler. However, corner speeds went down by about 8 miles per hour.

Cars with a lot of downforce can run anywhere on a track the drivers chooses. The shortest way around the track is typically the fastest. Everyone wants to run that line. Passing requires traveling a longer distance, which is difficult when cars are so close in performance.

Josh Wilson, Chevy’s motorsports engineering group manager for NASCAR aerodynamics, explains that cars with less downforce give drivers more options. Drivers will have to experiment with how they enter and exit corners, how quick they hit the brake and throttle, and where on the track they can make their car work.

In theory, that should all lead to more passing and better racing. But will it work in Phoenix?

“I don’t think it’ll be worse,” Bubba Wallace’s crew chief Bootie Barker told me. But he views the Next Gen’s new short track package as a first step. Because the diffuser bolts together, it was relatively easy to remove strakes. More significant changes require single-source suppliers to fabricate enough new pieces to supply all the teams.

Is one car for all tracks achievable?

NASCAR intended the Next Gen to produce great racing at any track using the fewest different rules packages. Superspeedways, of course, require unique configurations. As does the Bristol dirt race.

At the start of the 2023 season, NASCAR added select short tracks to the list of road courses requiring cars to run a wet-weather package.

The desire to minimize the number of distinct rules packages is why the new short track changes will not be used at Bristol or Dover. The banking and speeds at these tracks are too high for the wet-weather package. If NASCAR had added the new aero package to these tracks, teams would have to have tested the short track package with and without the wet-weather package. Each test costs money.

How NASCAR balances the needs of different tracks with the one-car/all-tracks concept remains to be seen.