How to Adjust Your Derailleur: Part One
By the end of this tutorial, you should:
Be able to identify when a standard rear derailleur needs tuning
Be able to tune a standard rear derailleur
Identify the important parts of a standard rear derailleur
Understand the tools needed to tune a derailleur
Have a better understanding of your bicycles workings
Tools You Will Need:
Philips screw driver
5mm Alan wrench
A willingness to get your hands dirty
7 steps to a better shifting derailleur
Step 1: Prepare your bicycle for derailleur tuning
Before you start to tune your rear derailleur, you’ll need to get your bikes wheels off the ground. One way to do this is to use a bicycle stand that holds your bike about a foot in the air. A cheaper way is to just flip your ride upside down, resting the bike on the handlebars and seat. Because I don’t own a bicycle stand (and I’m betting you don’t either) we’ll take the later approach.
Step 2: Identify your derailleur and it’s parts
Take a few moments to look at your rear derailleur. If you have never worked with this piece of your bicycle before, then it probably looks like a random collection of cogs and springs. The important thing to remember is that the rear derailleur is a simple mechanism that you can adjust, and that there are only a few specific parts to concern yourself with. Take a look at the close up of my own derailleur below.
For the purposes of tuning, the important parts of your derailleur are:
You will probably use all five of these parts to adjust your rear derailleur.
Step 3: Adjust the B screw
The purpose of the B screw is to adust the angle of your derailleurs body (B is for body, get it?) from the gears. The B Screw is the first of three limiting screws you will use to tune your derailleur. Use only quarter turns when tuning any of these three screws. The basic strategy should be to make a small quarter turn adjustment, check the results, then make another quarter turn if needed, check the results etc.
Shift to the largest gear and take note of the distance between the largest gear and the top derailleur cog. If the cog is rubbing on the gear, tighten the B screw clockwise to increase the distance betweeen them. If there is a large gap between the top derailleur cog and the largest gear (say, more than an inch) then turn the B screw counter-clockwise to decrease the distance between them.
Step 4: Adjust the L screw
The L screw is designed to limit how far the derailleur can move the chain on the lowest (or biggest) gear. If the L screw is not adjusted properly, the chain may not move onto the lowest gear, or it might move to far and fall onto the spokes of your wheel. As with the B Screw, use only quarter turns to adjust the L screw.
With the chain on the lowest gear, turn the pedals and get behind your bike to see how the chain sits on the gear. It should be perfectly centered on the gear. If it looks like it wants to ride off into the spokes, tighten the L screw clockwise to pull the chain away from the wheel. If it looks like it wants to fall off onto a higher gear, tighten the L scew counter clockwise. Continue adjusting until the chain is centered on the highest gear.
As a safety check, gently push the derailleur towards the wheel while turing the pedals. The chain should be limited by your L screw adjustment, and should not fall off into the spokes.