Derailleur gears by 13 drive-train. Most road bicycles have two chainrings, and touring bicycles commonly have three. The rear derailleur serves double duty: moving the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur. In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain. Sometimes the rear-derailleurs are re-purposed as chain tensioners for single-speed bicycles that cannot adjust chain tension by a different method. Although variations exist, as noted below, most rear derailleurs have
French articles and determiners the English definite article "the", although they are sometimes omitted in English. The French definite article can vary according to the gender (feminine or masculine) and number (singular or plural) of the noun. The definite article takes the following forms: Like "the", the French definite article is used with a noun referring to a specific item when both the speaker and the audience know what the item is. It is necessary in the following cases: Unlike "the", the French definite article is also used with mass nouns and plural nouns with generic interpretation, and with abstract nouns. For example: The