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Dr. Diandra: Dishing the dirt on racing the Next Gen car at Bristol

Kim Coon, Kyle Petty, and Dustin Long preview what to expect when the Cup drivers take to the dirt for the third time at Bristol, with Petty saying he expects to see aggression and Long predicting chaos.

Racing the Next Gen car at Bristol requires the most modifications of any track on the schedule.

Even the tires are different.

Here are three other ways the Next Gen car becomes a dirt car, just for this weekend.

Keeping dirt out of where it doesn’t belong

The primary challenge of dirt racing is that it’s dirty.

The last place you want dirt is in a high-tech engine with the tightest of clearances. A throttle-body air filter is permitted at all tracks, but essential at Bristol.

The second-last place you want dirt is embedded in your radiator. Radiators use airflow to cool water coming from the engine. Without airflow, the engine could overheat.

The radiator air inlet sits in the center of each car’s front fascia. Although each manufacturer’s fascia styling is different, the openings are the same. The diagram below shows a Ford’s front fascia. Red indicates the areas where up to two 4”-diameter brake duct openings can be put on each side.

A graphic showing the radiator air inlet on a Ford

Teams place grates over the radiator air inlet openings at all tracks. When running the Next Gen at Bristol, they use an additional screen with a fine-mesh filter fabric placed not more than 2 inches in front of the usual screen. Air can flow into the radiator around the top, bottom and sides of the extended filter, while mud is captured. The mesh can be changed out as needed.

Stewart Haas Fords used white screens in 2022, making them the easiest cars on which to see the feature. Although the photo below makes it look like the extended screen is right in front of the fascia, there’s actually more than an inch between them.

NASCAR Cup Series Food City Dirt Race - Qualifying

The protrusion at the very bottom of the screen is a camera — this one with a rather large glob of dirt on it.

The photo below shows a Gen-6 Ford fitted out for dirt racing. The extended splitter of the Gen-6 practically invites dirt to build up.

Then again, no one ever expected the Gen-6 car to race on dirt.

NASCAR Cup Series Food City Dirt Race Practice

Although dirt still accumulates on the front of the Next Gen car, its much smaller splitter prevents the heavy buildup seen on the Gen-6 car.

Getting to the bottom of the issue

The biggest change comes underneath the car. Given the banking and slower speeds, racing the Next Gen car at Bristol doesn’t require a lot of downforce.

At Bristol, a “dirt event debris shield” replaces the underwing. I’ve omitted some of the smaller underwing parts in the diagram below for the sake of clarity.

A graphic comparing the underwing used on all pavement tracks to the dirt event debris shield used at the Bristol dirt race

The graphic shows how much the splitter has been minimized. Even the dirt racing engine panel lacks the contouring of the underwing.

And although the center sections (dark blue in the regular underwing and salmon in the dirt event debris shield) look similar, they aren’t. Finally, the rear diffuser and all its strakes are replaced by simple panels designed more to shut out dirt than for aerodynamics.

Dirt Track Vision

If race cars create vortices at pavement tracks, they create dust devils at dirt tracks. One lesson learned after the first Bristol dirt race is that night racing is a must.

“There’s a reason,” Chase Briscoe said, “that, when we go dirt racing any day of the year, we race at night. A day show is very rare. When you run a day show, it’s always dusty, it’s always a struggle to see and the track’s not very good.”

Even if the track offers up dirt rather than dust, visibility remains a problem. One glob of dirt in the wrong place on a windshield can make it impossible for a driver to see where he’s going.

Most cars that race on dirt have wire screening in place of windshields. Last year, Larson — who has perhaps the strongest dirt credentials in the Cup Series garage — advocated for removing the solid windshields on the Next Gen racecar.

“I feel like we’re just wasting everybody’s time a little bit and not giving the fans and competitors what we all deserve,” he told SiriusXM NASCAR radio. “So in my opinion, if we’re not going to take the windshields out, we might as well just never put dirt on Bristol again.”

But the laminated polycarbonate windows will stay in place for Sunday’s race. Although the visibility challenge remains (especially having only between-stage-break pit stops) safety concerns dictate that the windows stay put.

Any number of parts on a Next Gen car are heavy enough to go through wire. No helmet could protect a driver from a piece of lead or titanium ballast, for example.

While NASCAR can no doubt develop a viable replacement for windshields, it’s less of a priority given that the Next Gen car races on Bristol dirt only once a year.