Here is an interesting article describing the first time that aerodynamics was taken into consideration when designing an automobile. The resulting car had a streamlined front end, boattail, smooth underbody paneling, and went much faster on much less horsepower than any of its contemporaries. It wasn't until 1924 that another car was built (the Rumpler Tropfenwagen) that was anywhere near as streamlined as the Rocket, but it went the next logical step in aero design by enclosing and streamlining the cockpit.
http://www.steamcar.net/stanley/fastest.pdf