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
Influence of French on English chose to stay in England moved further away from France and, therefore, from the French language. Keeping its status as the language of justice and the language of power, England saw the first teaching manuals for teaching French to the English. These manuals were intended for English nobles who wish to perfect their knowledge of French and taught it to their children. Two types of French spoken in the higher spheres of English society could be distinguished during the thirteenth century : the Anglo-Norman dialect, which was the aristocrats' mother tongue, and a more prestigious type of French as a