Tip #1: Adjust your high-limit screw
Your high limit screw will be on your rear derailleur and is usually marked with an H. This screw will limit the amount of range of your rear derailleur. If your high limit screw is off, then your chain might come off your *Smallest* cog and shift outboard too far. This limit adjuster prevents your bike from shifting over the limit of the smallest cog outward. To make the adjustment:
- Make sure the bike is in the biggest front chainring
- Make sure you've clicked the rear derailleur all the way into the smallest cog as possible.
- Adjust the barrel adjusters if any so that they are de-tensioning the shifter cable
Once this is all done, you can align your rear derailleur pulley wheel with the cog by turning the H limit screw clockwise until you hear the drive train become noisy. Once it's noisy, back the screw out until the noise is gone, and you have a smooth-running chain.
Tip #2: Adjust the indexing
The purpose of this adjustment is to make sure the derailleur lines up with each cog. The first step is to ensure the chain is on the correct front chainring. If you have a double, make sure it's on the biggest chainring. If you have a triple, make sure it's in the middle chainring.
Adjusting the indexing takes a bit of trial and error, but we can do it systematically so that our results are repeatable, and we minimize the work. The first step is to shift your rear derailleur into the smallest cog. Once we're in the smallest cog, shift up one single click. If the chain does not make it to the next gear, return the gear to the outermost cog using the shift lever and then turn the barrel adjuster on the rear derailleur one turn counter-clockwise. Repeat this step until it makes the step.
If your shift lever is shifting multiple sprockets, in the rear, that means your shift cable is too tight, and tension must be taken out of the shift cable by turning the barrel adjuster clockwise.
Now we fine-tune the rear cog since we have the general setup done. Shift up and down the sprocket and check for noise. If there is excessive noise, turn the barrel adjuster clockwise just a quarter turn and check for excessive noise. Repeat until the sound is no more. Repeat this for all sprockets.
Tip #3: Adjust the Low Limit Screw
The key here is to adjust this screw too tightly and then back it out. This limit screw offers protection from going off the biggest cog and into the wheel spokes. To begin, shift your chain to the next smallest chainring. If you cannot get into the largest rear cog, if it shifts slowly into the largest cog, or there's a ton of noise in the largest cog, then your L screw is already too tight. Loosen the screw a quarter turn at a time until you can make it into that biggest rear cog properly.
The key here, like the other parts of this job, is that we need to tighten the L screw until we create symptoms of an L screw that is too tight, then loosen it one half turn. The symptoms we're looking to create are:
- Slow shift into biggest rear cog
- Noisy chain in biggest rear cog
- No shift whatsoever into biggest rear cog
To check your work, try to shift the rear derailleur past the low limit while your bike is stationary. Watch and see if the rear derailleur can move past that largest cog. If it moves, you've done something wrong.
Tip #5: Adjust the B screw
The B Screw makes your shifting snappy and quick. What it does is pulls the derailleur wheels closest to your biggest cog. To check this, put your bike in the smallest chainring and largest rear cog. Most manufacturers recommend a 5 mm gap between your rear pulley and the largest rear cog. If the gap between your derailleur and largest rear cog is too small, your drivetrain will sound loud and crunchy. To increase the gap, turn the B screw clockwise.
Tip #6: Ensure that your chain and sprocket isn't overworn
Having a worn-out chain and sprocket will make this task infinitely more difficult. If you're noticing that no matter what you've done, the bike won't get into gear properly, it could be because of a worn-out component. In my experience, chains begin to show signs of wear after 2000 miles. Cassettes don't wear out too fast but riding a worn chain on a cassette will wear it out faster. Terrain will likely be the largest factor here.
If you've completed all these steps, your derailleur is properly adjusted.