How Stock Car Aerodynamics Work


Stock Car Drag

Aerodynamic drag is the force of air along the length of the traveling car, opposing the car's force. As the car cuts a path through the air, some air molecules collide with the front bumper, producing resistance.

­Other molecules flow along the hood, only to come up against the windshield -- another source of drag. The air that glides smoothly over the roof grows turbulent above the rear window and behind the car, exerting a backward force on the vehicle.

Speed, air density, and car size, shape and design all determine the magnitude of a car's drag force.

"A faster car experiences more drag because it has to push air molecules out of the way faster," Diandra Leslie-Pelecky explains in her book, "The Physics of NASCAR." "Dense air increases drag because there are more air molecules hitting each area on the car. A larger cross-sectional area increases drag because more air molecules have to be moved out of the way" [source: Leslie-Pelecky].

Drag is the major obstacle to acceleration and racing speed. A passenger car driving on the highway spends an estimated 60 percent of its energy overcoming air drag, a far greater percentage than tire friction and the energy needs of the drive train itself [source: Beauchamp].

Defeating drag was the first major focus of automotive aerodynamics, beginning in the 1960s. It is still the most important variable in racing conditions that place a smaller premium on downforce, such as longer tracks with more straightaways.

The sleek lines, tilted windshields and rounded corners of modern race cars -- and passenger cars for that matter -- are designed to minimize drag. But the quest to engineer racecars with high net downforce sometimes leads to additional drag. The rear spoiler found on NASCAR vehicles is a case in point: It increases drag by distributing weight from the front to the back of the car [source: Circle Track]. Aerodynamics remains a vibrant and young field of engineering, with many innovations still to come down the road.

To keep up with the latest innovations in aerodynamics, visit the links below.

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Sources

  • Associated Press. "Going With the Flow." (Accessed 12/15/08) http://hosted.ap.org/specials/interactives/nascar2005/aerodynamics/aerodynamics.swf
  • Beauchamp, Warren. "Passenger Car Aerodynamics." (Accessed 12/15/08) http://www.recumbents.com/car_aerodynamics/
  • BMW. "BMW Side Skirts." (Accessed 12/17/08) http://www.bmwsideskirts.com/history.php
  • Boone, Jerry F. "Bad Air? The Physics Behind Auto Racing." Stock Car Racing. (Accessed 12/14/08) http://www.stockcarracing.com/techarticles/scrp_0301_the_physics_behind_auto_racing/index.html
  • Boone, Jerry F. "Race Car Aerodynamics - Short Track Auto." Stock Car Racing. (Accessed 12/14/08) http://www.stockcarracing.com/techarticles/scrp_0702_race_car_aerodynamics/index.html
  • Circle Track. "Aerodynamics - Stock Car Aero Defined." (Accessed 12/14/08) http://www.circletrack.com/techarticles/0304_aerodynamics_tech_definitions/index.html
  • Cislunar Aerospace. "Aerodynamics and Race Cars." K-8 Aeronautics Internet Textbook. (Accessed 12/15/08) http://wings.avkids.com/Book/Sports/advanced/racecar-01.html
  • ESPN. "Aero Push." (Accessed 12/14/08) http://sports.espn.go.com/rpm/nascar/icons/news/story?id=3426389
  • Hiestand, Michael. "ESPN Will Show the Unseen of NASCAR." USA Today, July 24, 2007. (Accessed 12/15/08) http://www.usatoday.com/sports/columnist/hiestand-tv/2007-07-24-ESPN-NASCAR_N.htm
  • Leslie-Pelecky, Diandra. The Physics of NASCAR: How to Make Steel + Gas + Rubber = Speed. Dutton: 2008. (Accessed 12/17/08 via Google Books) http://books.google.com/books?id=OAK3yFlHoTAC
  • Tierney, John. "NASCAR's Screech and Slam? It's All Aerodynamics." New York Times, February 12, 2008. (Accessed 12/15/08) http://www.nytimes.com/2008/02/12/science/12tier.html?pagewanted=all
  • Turner, Charlie. "Drafting and Aero." Bench Racing with Steve and Charlie. (Accessed 12/16/08) http://benchracing.typepad.com/bench_racing_with_steve_a/drafting_and_aero.html

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