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. This is usually due to 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:
Simple Adjustment Derailleur designers provide a simple way for you to dial in shifting. You don't even need tools (although, it's easiest to make and check adjustments when the bicycle is supported in a repair stand). Note: we are assuming that your derailleur and derailleur hanger are not damaged or bent. If you suspect that it is, it needs more than this simple adjustment and you should bring your bike in to us for servicing (read the sections that follow for more information).
To adjust the derailleur, look at the point where the cable enters the rear derailleur in the photo. See that silver winged knob-like piece inside the red circle? That's a barrel adjuster, which is used to tune the derailleur adjustment.
Standing behind the bike, the barrel adjuster is turned either counter-clockwise or clockwise in half-turn increments until the shifting hesitation is cured. Which way do you turn it? It depends on what type of hesitation you're experiencing. The most common problem is slow shifting into easier gears (toward the spokes) due to the cable stretching. But, it's possible that you're experiencing the opposite.
This rule will help you remember which way to turn it: If the derailleur is hesitating when shifting towardthe spokes (the more common problem), turn the barrel towardthe spokes (counter-clockwise); and if it hesitates shifting away from the spokes, turn the adjuster away (clockwise) from the spokes. (Always turn it only a half turn, shift multiple times to check the adjustment, and repeat as needed to cure all hesitation.)
Protect That Derailleur Another adjustment needed is an "attitude" adjustment. It's important to always remember that the rear derailleur is fragile and must be protected. This is worth emphasizing because there are many times that the derailleur is at risk, such as during flat-tire repair (always lay the bike down gently on its left side so the derailleur doesn't touch the ground), while shipping a bike (shift onto the largest cog and pad the derailleur), during transportation (always lay the bike drive side up and NEVER lay anything on to of the derailleur) and even parking your bike (make sure that if it topples it drops onto the non-drive side). All it takes is the bike falling over for the rear derailleur or hanger to get hit and bent. Usually, we can fix the damage with special alignment tools. But, you can avoid the downtime by thinking of your derailleur as a delicate object and watching out for it.
Accidents Happen If you do manage to bend the derailleur or hanger, you may not notice until you get back on the bike. Once the derailleur is bent, bad things can happen such as shifting into the spokes, which may ruin the derailleur and might seriously damage the rear wheel and frame. Signs of having a bent derailleur include sudden hesitation shifting into harder gears and a rapid pinging sound when you're on your largest cog (shift out of this gear immediately if you hear this sound because the derailleur is hitting the spokes and may get pulled into the wheel at any moment). Bring your bike in immediately for us to check it if you notice these problems.
What Are Those Little Screws For? When many people decide to adjust their rear derailleur, they mistakenly try to do it by turning the small screws on the back of the derailleur (inside the yellow circle). These screws are related to derailleur adjustment and once they're set, which we do when we assemble the bicycle, they do not change adjustment. It's almost never necessary to turn them. In fact, if you do turn them, it usually worsens your shifting. Our mechanics ask that you please leave the limit screws alone or, at least, tell them when you have been messing with them. It will be far less expensive to be honest up front than to pay our mechanics $85/hour to chase down a problem or to buy a new bicycle after you drive your rear derailleur into the spokes.