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 French royal title, then the Flemish would be able to keep their honor, since they would not be attacking the "true King of France" (Edward III). Edward continued to use this title until the Treaty of Brétigny on 8 May 1360, when he abandoned his claims in return for substantial lands in France. After the resumption of hostilities between the English and the French in 1369, however, Edward resumed his claim and the title of King of France. His successors also used the title until the Treaty of Troyes on 21 May 1420, in which the English recognised Charles VI