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
Glossary of French expressions in English Glossary of French expressions in English Around 45% of English vocabulary is of French origin, most coming from the Anglo-Norman spoken by the upper classes in England for several hundred years after the Norman Conquest, before the language settled into what became Modern English. Thoroughly English words of French origin, such as "art", "competition", "force", "machine", "money", "police", "publicity", "role", "routine" and "table", are pronounced according to English rules of phonology, rather than French, and are commonly used by English speakers without any consciousness of their French origin. This article, on the other hand, covers French words and phrases that