"Da Vinci was a genius...he came up with the basic concept of the bicycle five hundred years ago," Ernesto Colnago told Cyclingnews.com at the EICMA Milano show. [Note: Cyclingnews removed this quote after this BikeBiz.com story was pointed out to them].
Da Vinci sketched many things in his time, but the bicycle was not one of them.
The bicycle-like sketch once attributed to Da Vinci was "discovered" in 1974 during the restoration of Vincis Codex Atlanticus.
Scholars have known the sketch to be a forgery since the mid-1990s.
There's an interesting history of the hoax here: