Adjusting your rear derailleur can be tricky. The same problem could have one or more different – but similar – causes. Your derailleur is going to need adjusting if it’s slow to shift up or down, if it changes gear all of its own accord when you’re innocently cycling along or if it rattles and clatters whenever you change gear. This is how you do it.
Adjusting your indexing: derailleur types – standard and rapid rise
Before you start adjusting, use the following method to check whether you have a standard derailleur (by far the most common on all bikes) or a rapid-rise derailleur. Change into one of the middle cassette sprockets. Take hold of any exposed part of the derailleur cable where it passes along the top-tube or down-tube of your bike, and pull the cable gently away from the frame. Watch the derailleur:
- If it moves towards a lower gear (larger sprocket), you have a standard derailleur – follow the instructions.
- If the derailleur moves towards a higher gear (smaller sprocket) when you pull the cable, you have a rapid-rise derailleur (lownormal). These were introduced a few years ago, but never really caught on, so there aren’t many of them about. They’re just as easy to adjust as standard pull versions – use the same routine, but start from the largest sprocket instead of the smallest.
When you adjust gears, you shift repeatedly through them to test what happens. Although there are different makes and models of shifter, they all work in the same way – adjusting your indexing will be the same process whether your handlebar gear levers are twistshifters, triggershifters or STi shifters found on road bikes. Start by experimenting to see what happens to the cable when you shift. Find an exposed part of the cable, like you did for checking whether you had a standard or rapid-rise shifter, and pull the cable gently away from the frame with your left hand. Holding it away, use your right hand to change gear. You won’t need to pedal at the same time, just operate the shifter. One movement makes the cable slacker, the other makes it tighter. Change up and down a few times so that you begin to remember which does what. For standard derailleurs, shifting so that the cable is tighter pulls the derailleur towards the wheel and onto a larger sprocket. Shifting to release the cable allows the derailleur spring to pull the derailleur away from the wheel, toward a smaller sprocket. Once you are familiar with the action of your shifters, you can start indexing your gears.
People often get confused with gear indexing, mixing it up with adjusting the end-stop screw. This is also important, but it’s different. The end-stop screws set the limit of the range of movement of the derailleur, stopping it from falling off either end of the sprocket. Sometimes they are set wrong and accidentally stop the chain from moving onto the sprockets at either end of the cassette.
If this is the case, you cannot adjust your indexing properly – go to the section on end-stop screws, adjust them and then return here. Always check before you start adjusting the indexing that the chain reaches the smallest and largest sprockets, without dropping over the edge of either.
To tune the indexing, you have to adjust the tension in the cable so that one click of the shifter changes the cable tension precisely enough to move the chain across exactly one sprocket. Pulling the cable moves the chain toward lower gears, the larger sprockets near the wheel. Releasing tension in the cable allows the derailleur spring to pull the chain outwards, towards the small sprockets.
Key points to check if you have trouble adjusting your cable tension
- Compatability – have you got the same number of clicks in your shifter as sprockets on your cassette? This is a surprisingly common cause of intractable adjustment problems.
- Derailleur hanger angle – the derailleur will only follow the shape of the cassette if the jockey wheels hang vertically below the sprockets. Crashes often bend the derailleur or the derailleur hanger inward, so that the derailleur sits at an angle and will not respond to adjustment.
- Crusty cables – the cable must be in good condition so that the shifter can pull through precise amounts of cable. This makes the most difference when the shifter releases a length of cable. The spring in the derailleur will not be strong enough to pull through cable that’s gummed up with mud or rust.
“Crashes often bend the derailleur hanger inward”
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “Indexing: the delicate science of slipping from one gear to the next”