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

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.

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.

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 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