The measurement used to show how aerodynamically efficient or slippery a car is is the drag coefficient and is given as a Cd factor. Most modern cars would have a Cd factor of around 0.30 to 0.50, with the lower figure representing the car with less drag. To obtain the Cd factor, wind tunnel tests are conducted and each of the different forms of drag are measured. These different forms are form drag, lift drag, interference drag, friction drag, and internal air flow. The proportion of the total drag that each of these various forms produce is approximately 55%, 7%, 18%, 8%, and 12%, respectively. The Cd factor is calculated from the total drag, the air density and speed, and the frontal area of the car. There is no standardized system of measurement for determining the frontal area of the car, making the drag coefficient figures a little unreliable. Despite this, however, the Cd factor can be useful when comparing cars of a similar size.

  • Corporate Authors:

    Southern Africa Commercial Travellers Association

    Box 828
    Cape Town,   South Africa 
  • Publication Date: 1984

Media Info

  • Features: Photos;
  • Pagination: p. 19-22
  • Serial:
    • On the Road
    • Publisher: Southern Africa Commercial Travellers Association

Subject/Index Terms

Filing Info

  • Accession Number: 00393905
  • Record Type: Publication
  • Source Agency: National Highway Traffic Safety Administration
  • Report/Paper Numbers: HS-037 728
  • Files: HSL, USDOT
  • Created Date: May 31 1985 12:00AM