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
What Is a Nation? Language, by contrast, "invites us but does not force us, to unite". Countries which share the Spanish or English language don't merge with one another, while the people of Switzerland speak several languages. Modern nationhood also cannot be based on religion, which Renan observes, is currently practiced according to individual belief. "You can be French, English, German, yet Catholic, Protestant, Jewish, or practicing no religion". Mutuality of interests is fine for corporations and their affiliates, but nationality is based on sentiment. Geography merely leads us astray, and often to violence: "Mountains don't know how to carve out countries". Renan concludes