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A spate of fiery crashes in the run-up to Sunday's Indianapolis 500 has raised questions about new body kits outfitting cars that average more than 200 miles per hour.
On a Wednesday practice run, Brazilian driver Helio Castroneves completely flipped his car. The next day, Josef Newgarden experienced a similar crash, except his car never landed back on its tires. Instead, it slid across the track upside down in a streak of smoke and sparks. The same thing happened to Ed Carpenter two days later.
None of the drivers was seriously injured. The same can't be said for James Hinchcliffe, who lost a significant amount of blood on Monday after a piece of his car's suspension pierced his left thigh during a fiery crash. On Wednesday, the Verizon IndyCar Series said that Hinchcliffe was expected to recover.
Crashes aren't new to the Indy world. But four dramatic wrecks in less than a week?
"This is not normal," Chris Finch, a professor of motorsports engineering at Indiana University-Purdue University Indianapolis, told NBC News.
Why this Indy 500 is different
From 2012 up until March, every IndyCar driver has been steering the same vehicle. The cars might have had different paint jobs, logos and drivers, but underneath they were all the same Dallara DW12 chassis.
Then IndyCar decided to mix things up with aero kits. Honda and Chevrolet both released two of them, one for road courses and another for speedways, priced at $75,000 per pair.
The kits basically change the aerodynamic properties of a car, allowing teams to optimize their cars for the best performance. Also, they look cool.
More variety gives fans more to look at, letting them cheer for visually distinct Honda and Chevy cars. But they are relatively untested. The road kits made their debut in March at the Grand Prix of St. Petersburg. The speedway kits will first see action on Sunday at the Indianapolis Motor Speedway.
What went wrong?
It's too early to blame the aero kits for the crashes. Drivers lose control for all kinds of reasons. But several experts told NBC News that this didn't seem like a coincidence. The first three drivers who crashed — Castroneves, Newgarden and Carpenter — all drove cars with the Chevrolet kits.
Hinchcliffe, who was more seriously injured, was driving a Honda car. His accident is believed to have been caused by a mechanical failure with his front suspension.
It's the accidents with the Chevrolet cars, however, that have raised some questions.
"I'm convinced that this has something to do with the aero kit package," Mesbah Uddin, director of UNC Charlotte's Motorsports and Automotive Research Center, told NBC News.
General Motors, which owns Chevrolet, said it was looking into any possible connection.
“Our engineers continue to analyze the data from the recent incidents at the speedway," Jim Campbell, vice president of performance vehicles and motorsports at General Motors, told NBC News in a statement. "We continue to share our findings with IndyCar, Honda and Dallara. The most important part of this conversation is safety."
Finch thinks the crashes probably had something to do with the Chevrolet kits. He worked as a race engineer for 20 years before entering academia and is currently under a temporary contract with Schmidt Peterson Motorsports, a Honda team.
In his opinion, he doesn't think the Chevrolet aero kits malfunctioned. Instead, he thinks that they might have made the cars less forgiving, causing drivers to crash in situations where they previously could have recovered.
"That is the only scientific rationale I can come up with in my head," he said. "When you're pushing the car to its absolute limit, the margin of error is very small for the driver."
Uddin watched and discussed footage of the crashes with Robert Dominy, a professor of automotive engineering at Northumbria University. They both came to the same conclusion: the aero kits — both for Chevrolet and Honda — could lead to accidents by making the area of the car behind the rear wheel wider, making the car more likely to flip.
"You have to go in and reevaluate"
Teams often like to make cars "loose" for qualifying rounds, which means the rear tires lose traction before the front tires. That makes it easier to take turns faster, but can sometimes result in a car fishtailing.
The aero kits are meant to provide downforce — downward thrust that increases the grip of the tires, which helps cars take turns faster. In each of the Chevrolet crashes, the driver was too loose on the turn, tried to correct himself, hit the wall and then flipped.
When a car pitches upward, Uddin said, the aero kit acts as a lift device instead of providing downforce. That might be related to the fact that the aero kits have widened the area behind the rear wheel, he said.
Honda would not comment on Chevrolet's kit, but said that its own kit was safe.
"Our own data says that the Honda aero kit is in fact safer with respect to take off than the DW12 which it replaced, and IndyCar needed to be satisfied with this improvement before our car was approved for racing," Steve Eriksen, vice president and CEO of the racing arm of American Honda, told NBC News in a statement.
Uddin hopes that IndyCar doesn't scratch the kits altogether.
"I really like the idea of the aero kits," he told NBC News. "You don't want to strangle innovation. However, this behavior needs to be studied further."
What happens now?
Both Uddin or Finch stressed that they don't know for sure what happened. IndyCar hasn't attributed the crashes to the new aero kits.
"The cause of all the accidents this month have been different," Mike Kitchel, director of communications for IndyCar, told NBC News in an email. "As part of our standard process, IndyCar examines every race incident and analyzes all available data to make enhancements and improvements to our racecars. We’ve collaborated with our manufacturers to analyze and define any possible concerns."
It's too close to the Indy 500 for additional testing. IndyCar said in a statement that because of the “three separate, single-car incidents” that both Chevrolet and Honda teams had to reduce their engine boost levels – which will lower their top speeds – and race in the same cars they used to qualify.
Uddin would like to see IndyCar ban any of the aero kit changes made to the cars behind the rear wheel and subject the new designs to further testing by an independent, third party using a wind tunnel or computer simulations.
The three drivers who crashed their cars with Chevrolet kits will compete on Sunday. Finch hopes that there will be no more serious accidents and that the tumultuous last few weeks will cause some introspection.
"You have to go in and reevaluate," he said. "I've been involved with drivers who have been hurt severely and it doesn't feel good. As part of this small community, you never want to see that."