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 in the original language, to the extent that they would not be understood (either at all, or in the intended sense) by a native French speaker. c'est la guerre: "That's war!", or... c'est la vie: "That's life!" or "Such is life!" Through the evolution of the language, many words and phrases are no longer used in modern French. Also there are expressions that, even though grammatically correct, do not have the same meaning in French as the English words derived from them. Some older word usages still appear in Quebec French. International authorities have adopted a number of words and