Fuel economy is just one of the goals that I see. I find that the high rpms and vibrations are okay for a half hour or so but beyond that, it just frazzles the nerves. Imagine riding in a freight train car for 8 hours straight. Your ears are hurting, your senses are all overstimulated and tired, you are physically drained from it all. I had a Gear Vendors behind a 727 in my Charger. Their .78 O/D ratio is not great but it did help freeway cruising.
