In a traditional single-crown structure, loads from the entire fork concentrate at the steerer/crown junction below the headtube. When compared to the Lefty structure, the Dual Crown Inverted structure allow for loads to be distributed evenly through the fork and headtube for maximum strength and stiffness.
The upper structure of the Lefty fork is 40mm. The crowns clamp to this larger diameter and help fight flex and add strength. In a traditional fork design, the crown attaches to more flexible, smaller diameter inner legs.
The lowers of a traditional fork feature large diameter fork tubes further away from the fulcrum of the headtube. This distance makes their stiffness less effective. The Smaller 32mm lower leg of the Lefty is positioned furthest from the fulcrum. This helps maximize materials as the leverage and force is least in this area.
In order to even get close to Lefty's stiffness and strength, traditional forks must add a lot of reinforcing material which adds large amounts of weight. The Lefty's unconventional design utilizes material more effectively so it will always be lighter, stiffer and stronger than a traditional fork.