Derailleur gears several standards in use, and in each the product of the derailleur's actuation ratio and the length of cable pulled must equal the pitch of the rear sprockets. The following standards exist. Some rear derailleurs, especially for mountain bikes, incorporate a clutch to keep the lower length of chain in sufficient tension to prevent the chain from striking the bottom of the chain stay, called "chain slap", and which can damage the chain stay. Clutches are also helpful in preventing the chain from derailing from the chain ring on systems without a front derailleur. The front derailleur only has to
Longest word in English major English language dictionaries is "pneumonoultramicroscopicsilicovolcanoconiosis", a word that refers to a lung disease contracted from the inhalation of very fine silica particles, specifically from a volcano; medically, it is the same as silicosis. The word was deliberately coined to be the longest word in English, and has since been used in a close approximation of its originally intended meaning, lending at least some degree of validity to its claim. The "Oxford English Dictionary" contains "pseudopseudohypoparathyroidism" (30 letters). "Merriam-Webster's Collegiate Dictionary" does not contain "antidisestablishmentarianism" (28 letters), as the editors found no widespread, sustained usage of the word in its