# Indexing adjustment
The indexing adjustment is the most frequently needed derailer adjustment. The detents (click-stops) that provide indexing are in the shifters, and the index adjustment sets the length of the cable so that the derailer is in the correct place to correspond with each click stop.
If a derailer is correctly adjusted when it is installed, this is the only adjustment that should have to be tweaked later on, to accommodate cable stretch, or when cables are replaced.
The indexing adjustment is an adjusting barrel located at one end of a length of cable housing. Many rear derailers have more than one index adjuster. All indexed derailers have an adjuster where the final loop of cable housing ends at the derailer itself. Many bicycles also have another adjusting barrel located so that it can be adjusted while you are riding. On mountain-bike-type shifters, this will be located at the shifter itself, just where the cable exits. On road bikes with handlebar-mounted shifters, there will usually be an adjusting barrel at the cable stop where the upper length of housing ends on the upper end of the down tube.
It doesn't matter which of these adjustments you use, use whichever is more convenient.
Before you try adjusting the indexing, shift to the highest gear (smallest sprocket.) Make sure that the shifter is in the position that allows the cable to be as loose as it can get.
Click the shifter to the first click after the fully loose position, then turn the pedals forward. The chain should shift to the second smallest sprocket. If it doesn't, it means the cable is too loose. Turn an adjusting barrel counter-clockwise to tighten the cable. Start with half a turn, then check again. It is very common for beginners to over-correct by turning the adjuster too far. Sometimes this will result in moving the indexing so far off that it sort-of works, except that the clicks are one notch off, so one of the extreme gears doesn't work properly, but the others appear to be OK. This is why it is important to check that the shift from the smallest to the second-smallest sprocket occurs in the right place on the shifter.
Fine adjustments are accomplished according to the following principles:
Shifting to larger sprockets is accomplished by tightening the cable;
if such shifts are slow, the cable is not tight enough--
turn the barrel counterclockwise to tighten it.
Shifting to smaller sprockets is accomplished by loosening the cable;
if such shifts are too slow, the cable is not loose enough--
turn the barrel clockwise to loosen it.
If the rear indexing works properly when using the large chainwheel but not on the small chainwheel, or vice-versa, this is often a sign that the rear derailer hanger is bent.