Derailleur gears by 13 drive-train. Most road bicycles have two chainrings, and touring bicycles commonly have three. The rear derailleur serves double duty: moving the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur. In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain. Sometimes the rear-derailleurs are re-purposed as chain tensioners for single-speed bicycles that cannot adjust chain tension by a different method. Although variations exist, as noted below, most rear derailleurs have
Longest word in English Sylvia Plath made mention of it in her semi-autobiographical novel "The Bell Jar", when the protagonist was reading "Finnegans Wake". "Supercalifragilisticexpialidocious", the 34-letter title of a song from the movie "Mary Poppins", does appear in several dictionaries, but only as a proper noun defined in reference to the song title. The attributed meaning is "a word that you say when you don't know what to say." The idea and invention of the word is credited to songwriters Robert and Richard Sherman. The English language permits the legitimate extension of existing words to serve new purposes by the addition of prefixes