The racing line is the line you would take to #1 carry as much speed through the corner as possible, or #2 carry as much speed INTO the next corner possible. So you'd use two corners, be slow through the first and faster through the next because the next corner leads onto a straight and you'd want maximum speed, like a hairpin leading onto a straight, you go in deep so you have more speed coming down the straight. In my view, when the rubber has been laid down like this isn't not the racing line anymore it's the groove, because rubber is actually on the circuit therefore that part of the track is more sticky than the rest.