|The Roper Steam Velocipede of ca.1867|
|Patent drawing for the Michaux-Perreaux Steam Velocipede of 1869|
|The Mission One electric sports motorcycle.|
|The Roper Steam Velocipede|
|The Michaux-Perreaux Steam Velocipede|
|The last development of the Roper Steam Velocipede, 1895|
|The Michaux-Perreaux at the Guggenheim's Art of the Motorcycle exhibit.|
: For more on the subject, see Thomas Kuhn's 'The Structure of Scientific Revolutions'.
: Even Cycle World's esteemed Kevin Cameron has argued that only the I-C engine counts as the true root of modern motorcycling, as "History follows things that succeed, not things that fail" (the statement itself a highly debatable claim on History!), while LJK Setright preferred to use the term 'heat engines', which includes steam, but excludes electric motoring. Recent and online versions of the OED use 'two wheels and a motor, without pedals' - which excludes most motorcycles of the 1900s-20s, which HAD pedals!
: There is much debate about exact dates on each of these machines; for this article, I call a tie, not having time to search the records for my own opinoin. M-P patented his velocipede in 1869, but Roper's machine seems to have appeared in 1867, although Roper never patented his steam vehicle designs.