Tech Tips: How to adjust a Rear Derailleur

The black magic of the mountain bike world that leaves many a rider swearing and throwing tools around the workshop whilst they scurry to the fridge to grab a beer, is the derailleur. Many of us can’t seem to figure out the rear derailleur and the more gears we got, the easier it was to get wrong. In fact, 12 speed drive trains are great when they are working but if they are even a smidgen out they can be far from forgiving. We took a look into rear derailleur setup and have tried to simplify the process so every rider can have super smooth shifting.

Step 1 – Set the High limits

High is low and low is high right? confused?

The first step is to set the high limit which basically means setting the derailleur’s movement on the fastest gears or the smallest cog. Make sure you have the gear cable removed for this one then grab a 3mm allen key or whichever size fits your given derailleur’s limit screws.

Make sure you are turning the screw that is marked ‘H’ or the one that is on the inside of the derailleur, closest to the wheel. You want to turn the screw and watch the jockey wheel move so that the jockey wheel sits almost directly under the 10 tooth cog, slightly to the outside.

Step 2 – Tighten the Gear Cable

Once you have down this, install your gear cable into the derailleur and pull it tight, torque the screw to 4Nm. Trim the cable as required and crimp a cable end on to keep things neat and tidy.

Step 3 – Set the Low Limits

Now its time to set the low limits, so go ahead and shift the gears so that the derailleur is on the lowest gear or biggest cog, these days for most of us it’s a 50 tooth. Now adjusting the ‘L’ screw or the screw that is on the outside of the derailleur, make sure the derailleur lines up with the largest cog and cannot go into the spokes or wheel. Super simple right?

Step 4 – Adjust the Cable Tension

Often the part of the process that has us scratching our heads is the cable tension adjustment at the barrel adjuster. To start with turn the barrel adjuster fully clockwise until it stops, then wind it back out three or four half turns and this is the point we start from.

Shift your gears to the 4th gear and then proceed to adjust the alignment so the derailleur jockey wheel sits directly under the 4th gear.

Turning the barrel adjuster anti-clockwise increases the tension and brings the derailleur closer to the wheel.

Turning the barrel adjuster clockwise decreases the tension and brings the derailleur back towards the frame or outside.

If the chain has trouble shifting up increase the tension, if it skips a gear decrease the tension.

Once you are happy with the shifting and it’s nice and quiet then its time to move on, don’t worry the more you adjust your gears the better you will get at it.

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Step 5 – Adjusting the B-tension screw

The B tension screw is the last step to achieve epic shifting, but it is one of the most important steps. If this isn’t done correctly it could mean poor shifting, especially if you are running 12 speed.

If you are running SRAM Eagle like many of us then it’s made so much easier using the Eagle B-tension tool. Simply place the tool on the jocky wheel and line up the teeth of the 50 tooth cog with the outline on the tool.

For those running Shimano 12 speed, the tool is on the derailleur itself and simply line it up with the outline on the derailleur cage at the rear.

For those running any other drive train a gap of about 5 – 6mm works well with most drive trains.

The Final Word

Derailleur adjustment need not be difficult and it certainly isn’t the black magic we all think it is, bikes are pretty simple machines after all. Hopefully this has helped guide you to smoother shifting and has simplified the process. If there is any other Tech Tips you want covered for the home mechanic then let us know in the comments below!


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