[Bicycle Bob]

I've been thinking that the best way to hinge a tight front skirt is from the top of the fender, so that it stays roughly parallel to the airflow when it opens. I think it would be adequate to let the tires rub on the skirt to push it open, although rolling elements could be added. At low speed, when you would usually want the skirts to open, only light retaining springs would be needed. To keep them closed at speed, it might be nice to supplement the spring with a large bellows fed by ram air. Speed-controlled latches would not allow skid recovery on ice. Mechanical interlinks with the steering system might have unfortunate feedback, but servos controlled from the steering wheel could be ideal. No rubbing; you'd just have to remember the extra width in tight spots.

In general, I think that fender skirts would benefit by overlapping the body somewhat, rather than filling the existing hole.