[Gerrelt]

Yes, those are called "wheel deflectors" or "wheel spats". I am planning to make a pair too.

These things can be found more and more on modern cars. Not only at the front wheels, but also at the rear.
I want to make a set for the rear wheels.
It can't be hard to make, it's just a piece of flat plastic/fibreglass that sits just in front of the wheels.
I only wonder how to determine the correct size and position in relation to the wheel..