There are three adjustments that need to be made to modern rear derailleurs

High and low limit screws

Indexing

B-limit

We will start with the high and low limit screws

Before starting, remove all tension from the shift cable by loosening the cable clamp screw

These are most easily adjusted with the chain removed from the bike, so it can be helpful to remove the chain as well

Locate the limit screws, these are found on the back of the derailleur (Shimano) and on side of the derailleur (Sram). They will have an H and L next to them

Adjust the high limit screw, this screw limits the derailleur movement to the outside, between the smallest cog and the dropout

Sight down the back of the bike, turn the screw until the upper derailleur pulley is centered or just slightly outboard (towards the dropout) from the smallest cog

Next, adjust the low limit screw

Extend the derailleur into the lowest gear (largest cog), while holding the derailleur, turn the limit screw to adjust the derailleur pulley so it is centered over the largest cog

Once you have adjusted the low limit, release the derailleur to it's relaxed position over the smallest cog

Now that the limits are set, we will adjust the indexing by adjusting the shift cable tension

Check to make sure the shifter is in the smallest cog (hardest gear)

Check the barrel adjuster on your shifter and derailleur (if it has one) to make sure they are in the middle of their range

Pull the shift cable through the rear derailleur until it is snug and tighten the pinch bolt

It is the cable tension that is pulled in specific amounts by the shifter that indexes the rear derailleur

While pedaling the bike, shift from the smallest cog to the next smallest cog.

If the shift is sluggish add cable tension by turning the barrel adjuster until the shift is crisp

Shift back to the smallest cog

If the shift is sluggish the high limit screw may need to be adjusted outboard more...

...or there could be drag in the housing that is not allowing the cable to release fully

ensure the shifting is crisp both up and down from the smallest and second smallest cog before moving on

Next, shift through the cassette

Adjust the barrel adjuster as needed to get crisp shifting through the cassette

You can check the alignment between the cassette cogs and the upper derailleur pulley by sighting down the cassette from the back of the bike.

Once the indexing has been adjusted, adjust the B-limit for the EX cog

Shift in to the EX cog

Adjust the B-limit screw so that there is a 5-6mm gap between the upper derailleur pulley teeth and the teeth on the EX cog or until the pulley is as close as possible but without rubbing the largest cog

You will be able to hear if the pulley is rubbing on the cog

You may need to install the longer B-limit screw included with the EX cog if you are unable to keep the derailleur pulley from rubbing with the stock B-limit screw

You can read more about adjusting the B-limit in our EX cog install guide

Check indexing and limit screws one last time before riding