The Fastest Face-Down, Head-First, Human-Powered Vehicle

This story implies an interesting point. There has to be rule that the Tour de France bicycles cannot be recumbent. With a recumbent land speed records of 80+ MPH this has to be a more efficient design.

A recumbent would get killed at the Tour de France because of the uphill sections. recumbent bikes go fast on a level or downhill section, but usually don't do well on uphills. Uphill puts the fell over the head and there is no ability to stand on the pedals when needed.

.. and road racers need to be able to steer round hairpin routes. I think this machine is only designed to go in a straight line.

These HPVs also tend to be quite heavy. Climbing a 7+% grade for 15+ km, you sweat every gram.

For time trials (solo rides against the clock which often feature flat courses), the UCI has detailed rules governing bike geometry to keep the bikes looking and behaving conventionally. I believe the rules still enforce the "double triangle" geometry but allow the rider to be positioned more aerodynamically. The bikes also have disk wheels, which degrade handling but are more aero.

In 1968 this guy showed up at a bike race with a bike similar to this but simpler. He had taken an ordinary bicycle frame and elongated it and placed a belly pad on top to lay down on. He claimed he could do 54 miles an hour in a quarter mile and a 70 top speed. Judging by the size of his legs and his speed on the practice laps I believed him. They wouldn't let him race because his bike was too radically different.