From the September 2019 issue of Car and Driver.

In August 2018, a journalist driving a McLaren 570S Spider overcooked a corner on California State Route 33 and flew off the road. I was in the passenger's seat. With the roof retracted, the 570S rolled twice before coming to rest 297 feet from where the Pirellis last touched asphalt, some 80 feet down a mountainside. There were no injuries. While the horrific sensations of the crash are etched in my memory, I had only a fuzzy idea of the speeds and forces that I survived. A NASA rocket scientist and an accident-reconstruction agency helped piece it together.

Launch

We started the right-hand turn at 78 mph, per Principia Engineering, the firm that simulated the incident using the car's specs and Google Earth road topography to arrive at the most plausible scenario. A half-second into the turn, we were already understeering over the centerline, having exceeded the car's maximum lateral grip of about 1.07 g's. A second later, we were at the edge of the road. Principia estimates the car began to fly at a speed of about 65 mph.

Illustration by Nicolas Rapp Car and Driver

Flight

"Your speed through the air was approximately equal to the speed at which you left the road," says Ryan Conversano, who has a doctorate in aerospace engineering and works for NASA's Jet Propulsion Laboratory (JPL) as an electric propulsion technologist. Factoring in the initial 65-mph speed and the estimated 40-degree slope of the hillside, Conversano puts our flight time at about three seconds, during which gravity accelerated the car downward. "The speed at your first impact would be higher than when you first left the road," he says.

Illustration by Nicolas Rapp Car and Driver

Impact

Our initial impact was at 85 mph, calculated by balancing the kinetic and potential energy when we left the road with the kinetic energy when we touched down. Because we left the road understeering, we were somewhat sideways. "The two wheels on the downhill-facing side of the car will hit first," says Conversano. "You'd hit and pivot, spinning over in a barrel roll." At first impact, we likely experienced about 50 g's of deceleration, a force that the human body can tolerate for just seconds. He suggested that had the car cascaded into an unyielding object such as a concrete wall, we might have experienced a momentary 200-g spike at impact. But fortunately for us, explains Conversano, "You're hitting relatively soft earth, which helps absorb energy, and you've got a glancing hit that carries you partially parallel to the hillside while you keep crashing." The McLaren's carbon-fiber tub and aluminum crash structures sloughed off energy as the car rolled down the mountain, which allowed us to walk away.

Second Chance

Principia Engineering created a second simulation in which the 570S uses all of its lateral grip and the entire width of its lane without ever crossing the center divider line. It requires driving a racing line, but the McLaren could have continued on without incident at approximately 60 mph.

Disclaimer: NASA, JPL, and the California Institute of Technology are not affiliated with and do not promote the companies mentioned in this article. Any and all analyses, results, and conclusions were generated independently by Ryan Conversano and are his alone.

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