On many new vehicles there are small, forward-facing deflectors in front of the rear wheels that look like small splash guards. What is the purpose of these? I assume they are for aerodynamic (fuel-saving) purposes. Do they have any other function?
These are called wheel flaps or sometimes wheel spats and on some cars you see them on the front wheels too.
The purpose is just as you have noted, aerodynamics. The leading edge of the tires is a significant contributor to the drag and this tiny addition splits the airstream around the tire enhancing the drag coefficient.