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 the century, to Henri VI and Marguerite in the 15th century, all kings of England married French princesses. These marriages made French the language of the English court for several centuries and were decisive in strengthening the use of French in England. This period (12th-15th centuries) is characterized by a massive influx of French words into Old English vocabulary. In 1204, under Philippe Auguste, Normandy was officially annexed to the Capetian royal demesne (previously, Normandy, though part of French kingdom, was largely autonomous, under the authority of its dukes, kings of England), politically isolating England from the continent. Normans who