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Front Derailleur 101

Repair & Tech Info - Bikeman Tech Info

Front Derailleur 101

Front derailleurs can be very specific to your bike frame and drive train.  Luckily a lot of the front derailleurs nowadays are made to work with many different configurations.  Here are some of the basic things to know to help you pick out a front derailleur.

Derailleur Mount - Clamp, Braze-on, E-Type
Clamp - The clamp size refers to the outside diameter of your seat tube where the front derailleur clamps to.  The derailleur clamp comes in three different sizes and are measured in millimeters or in inches, here are the different sizes offered:
28.6 mm (same as 1-1/8 inch)
31.8 mm (same as 1-1/4 inch)
35.0 mm (same as 1-3/8 inch)

Braze-On - Some frames have a front derailleur mount integrated with the seat tube and do not require a clamp, those are called braze-on front derailleurs.  You can purchase clamps to convert a braze-on style derailleur into a clamp mounted derailleur.

E-Type - Some front derailleurs are mounted by clamping them with the bottom bracket cup, those are E-type front derailleurs.  Usually an E-type derailleur should only be used if you don't have any other mounting point above the crank for a clamp or braze-on front derailleur.

Cable Pull
The front derailleur cables arrives at the derailleur from below or from above determining whether it is bottom pull or top pull.  Traditionally all road bikes use bottom pull front derailleurs.  Many new mountain bike front derailleurs are Dual Pull meaning that they can operate with a cable coming from either the bottom or the top.

Top Swing Front DerailleurBottom Swing Front Derailleur
Top Swing/Bottom Swing
The way that the derailleur cage moves in relation to the main pivot of the derailleur is referred to as Top Swing (aka Low Clamp) and Traditional (aka Bottom Swing or High Clamp).  In some frame designs the low clamp of a Top Swing derailleur is neccessary.  Most people here at Bikeman prefer Traditional front derailleurs.  We feel they hold up better over the long haul.

Other Considerations
Typically you have to match the style of the derailleur to the style of the shifter.  A Shimano road front derailleur should be used with a Shimano road shifter - using a Shimano mountain shifter with a road front derailleur won't shift well in most cases.

It is ideal to pair a "9 speed" compatible front derailleur with a 9 speed cassette and chain, the same as it would be for a "10 speed" front derailleur, cassette, and chain - though it isn't always completely necessary.  If you have a weird set-up give us a call and we can probably give you come pointers on how to make it work.

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