I have installed 60mm lowering spring kit to my lupo and it has helped on aerodynamics, fuel consumption and also coastin even on slower speeds.
Biggest difference is at tight corners. I have a coast down test route to my home which has 2 90 degree turn and one 70 degree turn. After installing that kit I dont have to cut so much to get same coasting distances. So the stiffer suspension dont eat the energy.
Old:
https://www.facebook.com/photo.php?f...type=3&theater
VS New:
https://www.facebook.com/photo.php?f...type=3&theater