ONE OF THE GREAT THINGS about modern derailleur drivetrains is that they’re easily fine-tuned should the need arise. How do you know? Usually, the symptom that tips you off that adjustment is needed is hesitation during shifts. You click the shifter but the chain doesn’t quite engage the next gear the way it used to.
The most likely cause for this is a shift cable that has stretched slightly, which happens to all cables. When the cable stretches, it does not move the derailleur far enough when you click the shift lever. Here’s how to adjust the derailleur so it shifts perfectly again: