The 2018 Audi RS5 is a subcompact car inside, but its exterior footprint is within a couple of inches of a Ford Mustang in every dimension. For what it’s worth, Mustangs are also subcompacts. Fastback coupes just aren’t very big inside. The RS5 is the top trim available in the A5 lineup, the A5 and S5 lie beneath it, with 252