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
Football (word) brother plays football in the States", it would be clear from context that American football is meant. Canadian French usage parallels English usage, with "le football" usually referring to Canadian or American football, and "le soccer" referring to association football. When there is ambiguity, "le football canadien" or "le football américain" is used. Rugby union football in Canada is almost always referred to simply as "rugby". In most of the English-speaking Caribbean, "football" and "soccer" are both used to refer to association football, but use of the word "football" is far more common. The exception is the Bahamas, where the