Before choppers, you had bobbers; before bobbers, you had cut-downs. Teens-era bikes were tall, with a high center of gravity and a long wheelbase. The cut-down is exactly what it sounds like: The neck and axle clips are both raised, which drops the center of gravity. The seat post is dropped too, so instead of sitting on the bike, you're sitting in it. The tanks are shortened, and the wheelbase is shortened, all to make the bike lower, faster, lighter, and more agile.