Tandem bikes are romantic for when you want another passenger at the back. But what happens when you don't? California based Calfee Design built a pair of custom tandem bikes that can be transformed into a single passenger bike with just a few simple tools.

The bike works by removing the second passenger's frame and replacing it with a shorter structure for a single rider.

It is pretty genius, but when you think of the $25,000 price tag, you can probably buy a few tandem and single seater bikes at one go. [Calfee Design via Gizmag]