Remember when Bobby Allison hit the catch fence at Talladega in 1987? Good! That'll save us some time. Do you remember why he hit the fence? Probably not. Allison punctured a tire in the dogleg; this caused his car to enter a spin, and that spin allowed a high pressure pocket of air to hit the cars underside, lifting it from the ground. Everyone agrees this is an important moment in the history of NASCAR because it introduced the restrictor plate and (by extension) pack racing to Daytona and Talladega. For my research, this event is more remarkable than previously thought because it is the only time a single-car accident resulted in someone hitting the catch fence.
There are plenty of cases of cars going airborne during multi-car crashes (Jimmy Horton at Talladega in 1993, Ricky Craven at Talladega in 1996, Geoff Bodine at Daytona in 2000, Carl Edwards at Talladega in 2009, Kasey Kane at Pocono in 2010, and Kyle Larson at Daytona this month to name a few). In particular I examined the last 3 crashes listed and found a common element. A car may enter a flat spin with its broadside facing forward, but it is reluctant to get airborne until it is struck by another car. As the sliding car must be going slower than the one that just touched it, the sliding car is forced to accelerate. Our sliding car is subject to the Laws of Motion; therefore, inertial forces alone are causing the car to lift on the forward-facing broadside and drop on the impacted side. That extra lift on the forward-facing side is what allows the high pressure air pocket to form under the car.
For 25 years, NASCAR has told us that restrictor plates are the lesser evil. There may be more crashes with more cars to a crash, but the crashes themselves are supposed to have gentler forces involved. From 1982 to 1987 Daytona and Talladega had a combined 17 races with a pole speed above 200mph (320km/h). Of those 17 races, only one involved a car hitting a catch fence. Between the 90's, the 00's, and whatever this decade is called I have named several instances of cars hitting catch fences. While correlation does not prove causation, this is evidence that single cars traveling faster than 200mph are less likely to hit a catch fence (and less dangerous) than packs of cars at lower speeds. Last Sunday Dave Despain called for slowing the packs down to 180mph (290km/h) for safety. While I have a lot of respect for Despain, I doubt Kasey Kane was going that fast at Pocono.
There have also been calls for building bigger, stronger catch fences. That is certainly a good start; however, it does not address the problem. The problem is cars hitting catch fences, not catch fences being too weak. We need to focus on how to keep cars on the ground before we reinforce the contingency.
During a preseason press conference, one NASCAR executive (I believe it was Robin Pemberton) attempted to explain that liftoff speed is not a hard number which can be reliably predicted. At the time I was frustrated with this explanation. Now that I've taken the time to examine the circumstances of these crashes, I understand his point.
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