The rear derailleur controls the gears on the rear wheel of the bicycle. When the gear shifter is operated, the derailleur forces the chain onto a different sprocket of the cassette.










To set up the rear derailleur, there are three controls. There are two screws, which control the high gear maximum throw and the low gear maximum throw:

High Gear Maximum Throw
The high gear maximum throw limits the minimum distance the rear mech can travel. If the throw is out of adjustment, the chain will not drop down to the top gear or it will jump off the cassette altogether.

Low Gear Maximum Throw
The low gear maximum throw limits the maximum distance the rear mech can travel. If the throw is out of adjustment, the chain will not drop onto the bottom gear or it will jump off the cassette into the spokes of the wheel.

Cable adjustment
The cable adjuster alters the length of the gear cable stretching between the gear shifter and the rear mech. If the cable adjuster is out of adjustment, the chain will not be able to either move up or down through the gears.

How to set up the controls
To set up the rear derailleur, the high gear maximum throw must be in line with the top gear (smallest sprocket), while the low gear maximum throw must be in line with the bottom gear (largest sprocket). The cable adjuster needs adjusting so that the derailleur is in line with each sprocket corresponding with the clicks of the gear shifter. In the test below the maximum throws are marked with red lines while the cable adjustment is shown by two blue lines which must be in line with each other.

Set up the rear derailleur below: