The smooth, rounded shape of both cars gives them a very low coefficient of drag - the amount of resistance the car generates against the wind as it rolls down the highway. (articles.orlandosentinel.com)
The new X5 retains much of its styling of the outgoing model, although a great deal of work has taken place to lower the coefficient of drag. (driving.ca)
«The particular mixture ratio means that our composite has a very low coefficient of friction. (sciencedaily.com)