Workshop: Adjusting the front derailleur and rear derailleur

BIKE Magazin

· 22.01.2015

Photo: Thomas Thiesen

Workshop: Adjusting the front derailleur and rear derailleur

Bike mechanic Super Dan solves every screwdriver problem. In this episode, he shows how to set up the front derailleur and rear derailleur correctly. Sram single-speed drivetrains require a sure instinct.

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Setting up a circuit may seem as complex as rocket science to many. "Basically, it's totally simple," waves Super Dan off. If you understand the basics, you can get to grips with any gearstick. In principle, there are only a few screws that lead to the goal. The rear derailleur and front derailleur are controlled by a Bowden cable, which directs the chain over the chainrings and sprockets of the cassette. To prevent the chain from falling sideways, the swivelling range of the rear derailleur and front derailleur must be set. Two screws each limit the range of action of the derailleur. The rear derailleur has an additional screw that defines the distance between the rear derailleur and the cassette. If the action radius of the front derailleur and rear derailleur is correct, only the tension on the shift lever needs to be adjusted. With more tension, the chain climbs more easily; with less, it is easier to shift down. That's it!

ALIGNING THE EJECTOR

Incorrect angle: The guide plate of the front derailleur is not aligned parallel to the chainring. Before making the adjustment, the angle and height, i.e. the position of the front derailleur, must be correct. The angle can only be adjusted with clamp front derailleurs. Direct mount front derailleurs are already aligned parallel ex works.

Correct height: The distance from the outer guide plate to the chainring tooth should be one to three millimetres for smooth gear changes. As the teeth vary in height depending on the chainring, you should orientate yourself to the largest tooth. The height of the front derailleur can be adjusted on almost all models (with the exception of the E-type).

LIMIT SWIVELLING RANGE

Use the screw labelled "L" to limit the swivel range of the front derailleur inwards towards the frame. "L" stands for low and refers to the low gears at low speed. If the chain is on the small chainring and on the largest sprocket at the rear, it must run past the inner guide plate without dragging.

The H-screw (for high) limits the operating radius of the front derailleur to the outside. If the chain is on the large chainring and the smallest sprocket, it must run just past the outer guide plate without dragging. The front derailleur must not move any further outwards when further pressure is applied to the shift lever, thus dropping the chain.

6 Images

Photo: Georg Grieshaber

Three screws bring the rear derailleur into the correct position. The adjustment on the gear lever ensures optimum tension. Precision is required for eleven-speed derailleurs.

Explanation of L-bolt and H-bolt, wrap and tensile stress

CHECK GEARSHIFT EYE

Before you adjust the rear derailleur, you should first take a look at the derailleur hanger. The rear derailleur can only be adjusted correctly if it is one hundred per cent straight under the sprocket set. If the derailleur hanger is bent, you will be wasting your time adjusting the derailleur.

LIMIT SWIVELLING RANGE

As with the front derailleur, the first thing to do with the rear derailleur is to limit the swivelling range and thus the radius of action. The rear derailleur is limited to the outside with the H-screw. To do this, shift to the smallest sprocket. The upper guide pulley of the rear derailleur must be positioned exactly under the smallest sprocket.

To limit the rear derailleur inwards, shift to the largest sprocket. Here too, the upper guide roller must be positioned exactly under the sprocket. Use the L-bolt to prevent the rear derailleur from moving further inwards when the lever is pressed again and the chain from falling into the spokes.

COVER

Use the wrap screw to set how far the rear derailleur, and therefore the chain, wraps around the sprocket. To do this, shift to the largest sprocket and measure the distance between the teeth of the sprocket and the idler pulley. With Sram rear derailleurs, the distance should be 12-16 millimetres (Shimano rear derailleurs 5-6 millimetres).

7 Images

Photo: Georg Grieshaber

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Workshop: Adjusting the front derailleur and rear derailleur

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