Rear derailleurs for touring bikes: precise gear changes at the rear wheel
The rear derailleur is responsible for gear changes at the rear wheel and, more than any other component, represents the quality of the entire groupset. When you press the right shifter, the rear derailleur pushes or pulls the chain on to the adjacent cassette sprocket. The gear shifter, rear derailleur, chain and cassette must fit together and be designed for the same number of gears on the rear wheel. When choosing the right rear derailleur, in addition to compatibility with the number of gears and size of the cassette, you should pay particular attention to the distinction between road bike and mountain bike components, as these use different shifting ratios for off-road and road groupsets and are not cross-compatible.