If we can have bikes and trikes then why not an n-wheeled vehicle called a n-ike? (just waiting for the ‘cease and desist’ letter from the world of humourless chinese trainer manufacturers).
Today’s invention is a simple way to make a bicycle frame using wheels. Two would be used to hold the rear axle and the seat. One more would be clamped between these to hold the drive sprocket. A fourth would be clamped to this one to hold the steering yolk.
With the two on the road that makes six wheels in total. This arrangement offers lightness, ease of manufacture, a way to reuse old wheels and the possibility of personalising the riding geometry by changing the clamping positions.