Edward Taylor and Alexandria Sage

German auto maker BMW Group is limiting its use of costly carbon fiber and turning to cheaper lightweight materials such as aluminum and steel for its biggest selling cars to keep profit margins high.
 
 Lighter cars consume less fuel or if they are battery-powered can drive for longer on a full charge, vital attributes for manufacturers seeking to score points with consumers and regulators.
 
 But there is a trade-off. Although carbon fiber is stiffer and lighter than aluminum, it is more expensive, and BMW faces tough choices on how to remain profitable as competitors close in with their own lightweight electric car offerings.