The science behind the extremely fast cars

THE PHYSICS OF NASCAR

By Diandra Leslie-Pelecky

Dutton, $25.95, 286 pages

REVIEWED BY JOANNE MCNEIL

Even diehard NASCAR fans might believe racing cars is not much different from driving a normal car extremely fast, but Diandra Leslie-Pelecky, University of Texas-Dallas physics professor and author of “The Physics of NASCAR” explains there is a lot more to it than that.

Her book explains the sport works at the “limits of what we understand about aerodynamics, structural engineering, and even human physiology … Crew members — even if they can’t recite Newton’s Laws of Motion — have used these principles since the sport began to makecars faster and safer. Although they might not use the same words I use, NASCAR drivers quickly develop an intuitive understanding of the principles of aerodynamics and kinematics—or they crash a lot.” This behind-the-scenes look at the science of the sport is an exciting lesson for those of us who might not have considered Newton’s laws since high school.

A NASCAR race car enters turn three at the Las Vegas Motor Speedway at 170 mph. That sounds extremely fast already, but it is even more impressive when you consider, as Ms. Leslie-Pelecky explains, a Boeing 757 touches down a runway at roughly the same speed. And a Boeing isn’t positioned, like a race car, just inches away from another vehicle while it travels at such a high speed. How are these vehicles designed to protect the driver and maintain shape in such high speeds?

Ms. Leslie-Pelecky starts explaining the skeleton structure of the vehicle — the chassis — works like the bones in your body. Drivers modify their vehicles depending on weather and tracks, “sheet metal gets put on and cut off, and engines, springs, and shocks are installed and removed but the chassis really is the car.”

National Association for Stock Car Auto Racing mandates certain sizes for parts and wall thickness for the same reasons the Boyscout Pinewood derby require cars under a certain weight — drivers need to start with a roughly even base. After that, it is up to the mechanics.

Teams customize the bodies of their cars not just to the type of tracks, but every individual track. Small changes in the shape of the vehicle can produce the difference between winning and losing a race. Even still, an unexpected change in the weather might turn a brilliantly crafted car into a “slug.” Good mechanics are extremely intuitive about the racetrack working conditions.

Next, Ms. Leslie-Pelecky describes the engines. She says “blowing an engine,” “throwing a rod,” and “melting down” are not just metaphors when it comes to engine trouble, the second most common reason a race car doesn’t make it to finish (accidents are first.) The parts can indeed melt . “Oh, yeah!” Andy Randolph a chemical engineering PhD and Bill Davis Racing’s engine technical director told the author when she asked if even the pistons melt. “You take something going at 800 horsepower and break it and lots of damage happens.”

You might have paid more attention in class if only your high school physics instructor were as succinct and understandable as Ms. Leslie-Pelecky. She explains “torque,” as “how fast the car can accelerate, and the amount of torque is determined by the force with which the pistons rotate the crankshaft. An engine’s torque is always measured at a specific engine speed. The engine speed is how many revolutions per minute (rpm) the crankshaft makes, and the engine produces different amounts of torque at different engine speeds.” It is, the “twisting ability, like you use for turning bolts … If you’re having a hard time loosening a lug nut, try using a longer wrench.”

But the book is not just a series of science lessons, there is also a lot of great storytelling to be found. Junior Johnson was a last minute entrant into the 1960 Daytona 500. On top of that, he wasn’t enthusiastic about driving a year-old Chevrolet, when Pontiac race cars were the fastest race cars at the time.

In practice runs, he was surprised to see he could keep up with the Pontiacs if he trailed right on their rear bumpers. He told Ms. Leslie-Pelecky, “they couldn’t shake me … I knew I was right about the air creating a situation — a slipstream type of thing — in which a slower car could keep up with a much faster one.”

Using this intuitive sense, Mr. Johnson paced himself until he trailed behind another driver. Coming off the second turn, the back glass of his opponent’s car popped out. “I think our speed and the traffic circumstances combined to create a vacuum that sucked that back glass right out,” Mr. Johnson said, recalling his eventual win.

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