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
English claims to the French throne of Aquitaine. However, in 1337, Edward, in his capacity as Duke of Aquitaine, refused to pay homage to Philip. The French king's response was to confiscate what was left of lands in English held Aquitaine, namely Gascony, thus precipitating the Hundred Years' War and Edward's revival of his claim to the throne and title of King of France in 1340. The decision to assume the title of "King of France" was made at the solicitation of his Flemish allies, who had signed a treaty that they would no longer attack the French king. They said that if Edward took the