Originally Posted by
unterhausen
if by "underseat pivot" you mean the suspension pivot, that's going to be something you need to have fabricated. Maybe go with a more mountain bike-like design.
The steering "underseat pivot" is somewhat comparable to head tube and headset on a conventional upright bike. The bearings inside the tube allow the whole front end to rotate on the rear seat portion of frame. I'm leaning toward adapting a mountain bike headset for strength. The rider's weight is concentrated right over this pivot point. In the drawing below, the pivot is below the "i" in flevo bike.