How to Choose Bicycle Derailleurs

There are two types of dérailleurs one controlling the gear shifting on the front chain rings the other controls changes on the cassette or rear gears. You can also see an article about how the shifters interact with the dérailleurs. Dérailleurs have subtle differences that perform the same function of switching the chain from one chain ring to another, or switching the chain from one gear to another on the cassette.

Difficulty: Moderate

Instructions

Front Derailleur comparison

1. 
    
   The derailleur on the left is for a triple crankset, the one of the right is for a double.

   The primary design differences between are focused on what type of crankset the chain is installed on the bicycle. A triple crankset utilizes a wider inside plate and is shorter in length. The front dérailleur type MUST match the type of chain ring set up and the left shifter of the bike. It is possible to change from a triple to double or the reverse crankset, but the dérailleur and shifter must be changes as well.

2. 
    
   Two derailleurs from the same product family, but for differrent uses.

   Rear dérailleurs have difference in design that are also driven by the number of chain rings as well as the number gears in the cassette. The dérailleur on the left with the longer cage is for use with a triple crankset. It is also frequently used with cassettes with less than 10 speeds, but is capable of working with 10 speeds. The dérailleur on the right is for use with a double crankset. The longer dérailleur is used on triple cranksets because greater range of movement of the chain is needed.

3. 
    
   Derailleur comparison

   The image below shows dérailleurs from the three primary manufacturers. The images on the left are of their professional race level components and the ones on the right are more enthusiast or closer to entry level. The main thing to notice here is that there are fairly obvious uses of different materials in the race versions. This is either titanium instead of aluminum or carbon fiber instead of titanium. The gears may also be different in the material or the quality of the bearings. A buyer of the race version is buying a lighter component, the difference measured in grams, at in a higher cost. An entire component group might strip a couple to few of hundred grams off the weight of the entry level group, but cost twice as much. Keep in mind a 1000 grams is about 2.5 lbs, so the difference may not be dramatic.

Tips & Warnings

• The first comparison factor with dérailleurs is driven by the chain ring and cassette set up.
• You can change chain rings from triple to double or reverse, but the front dérailleur and shifter must be changed too.
• The same change can be made with cassettes to add more gears, but the rear dérailleur and shifter must be changed.
• The materials used in a dérailleur will determine its weight and the cost. The more exotic the materials and the lighter and more expensive the dérailleur will be.
• Dérailleurs do need to be checked and tuned based on the cable stretching and use.
• A very small amount of very light Teflon-based oil put in the cable housing will help performance and the longevity of the cables.
• Do not attempt to tune or change the settings on your dérailleurs unless you know what you are doing. You will negatively affect your bike's performance.
• Check the dérailleurs for dirt and grime on a regular basis and gently wipe them down to clean them.

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