This is the third installment of our look at aerodynamics in cars. Part 1 was about the front splitter, Part 2 was about the rear wing, and today’s article will focus on the rear diffuser. The rear diffuser is used to shape and decelerate airflow from underneath the car. It was the cause of much controversy at the beginning of the 2009 F1 season, with Toyota, Williams, and Brawn GP having a so-called double diffuser that was assumed by the other teams to be outside of the rules. The double diffuser was allowed and made the 2009 spec F1 cars produce significantly more down force than the previous year’s spec. It is used in most forms of racing, on both prototype and GT class Le Mans cars and most formula cars, in addition to high performance sports cars. (continue reading…)