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
Ascent of the A-Word the book as an "often raucously funny account of what seems to be America’s most popular insult" which manages to be neither "exceedingly snarky" nor "overly academic and pretentious". Ascent of the A-Word Ascent of the A-Word: Assholism, the First Sixty Years is a 2012 book by the American linguist Geoffrey Nunberg which analyzes the history of the epithet "asshole". In "Ascent", Nunberg traces to World War II the origins of the word as an epithet, when it was used as a term of abuse for superior officers considered abusive or self-important. Following the soldiers' return home from the war,