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
Yiddish words used in English sometimes in the same sentence. For instance, the word פֿאַרקאַקטע may be spelled "farkakte", "ferkockte", "verkackte", among others. In its roots, though, Yiddish (whether used as English slang or not) is fundamentally mediaeval High German; although mediaeval German suffered from the same vagaries in spelling, it later became standardised in Modern High German. This list shall use the same conventions as Modern High German, with the exception of certain words, the spellings of which have been standardised. Furthermore, common nouns shall be left lowercase, as in English. Yiddish words used in English Yiddish words may be used in a primarily