Derailleur gears operates the lever while pedalling, the change in cable tension moves the chain-guide from side to side, "derailing" the chain onto different sprockets. For more information about the choice of particular gear ratios and sprocket sizes, see Bicycle gearing. "Derailleur" is a French word, spelled "dérailleur" in French, derived from the derailment of a train from its tracks. Its first recorded use was 1930. At least one notable bicycle industry author has attempted to promote the anglicized spelling of "derailer". As of 2013, however, neither Merriam-Webster nor the Oxford English Dictionary has an entry for "derailer". Various derailleur systems were
International Federation for the Promotion of Mechanism and Machine Science International Federation for the Promotion of Mechanism and Machine Science International Federation for the Promotion of Mechanism and Machine Science (IFToMM) is an organization that supports international exchange of researchers and engineers from the wide range of discipline related to Mechanical Engineering. To promote research and development in the field of Machines and Mechanisms by theoretical and experimental methods, along with their practical application. It was on September 29, 1969m at the Second World Congress on Theory of Mechanisms and Machines which took place in Zakopane (Poland), that two scientists, Ivan Artobolevski (USSR) and Erskine Crossley (USA), proposed to establish