Bike Derailleurs Review

The bike derailleurs are one of the more complex parts of a bike. They come in two parts, the front and rear. Their job is to move the chain from one gear cog to the next and take up chain slack over rough terrain or when the front derailleur shifts. Campagnolo derailleurs are some of the best on the market right now. 

Both derailleurs are controlled from the shifters on the handlebars. There is a separate shifter for each front and rear derailleur, normally right for rear and left for front. They are attached to the derailleurs by cables which are under tension. The derailleurs are spring loaded which is kept in check by the cable. As you push or pull the shifter is either pushes or pulls the cable which allows the sprint to move the derailleur. This movement is what allows the derailleur to change up or down the gears at your command.

The bike front derailleur is a fairly simple construction that bolts to the bike frame, an example of which is the Shimano Tiagra derailleur.. It’s job is to move the chain back and forth across the chain rings on the crankset. It’s a system which uses mechanical movement to force the chain across the rings to the desired gear. One way is spring loaded, so if the tension on the cable holding it in place is released it would push the chain to the outermost chain ring, which is the highest gear. This is called the “relaxed position” because there is no tension in the system. Pulling the cable increases the tension on the spring and moves it down.

The bike rear derailleurs, like the shimano rear derailleur, are often referred to as the “mech.” It moves the chain up and down the rear gears, and takes up chain slack. The mech is spring loaded in two directions to achieve this. One spring pushes the mech outwards and is held in check by the cable. The other pushes it backwards to allow it to take the chain slack. It’s the same principle as with the front derailleur. The position is dictated by the tension of the cable, which in turn is controlled by the position of the rear shifter. A quality front derailleur includes the SRAM front derailleur. 

The mech consists of the change mechanism and the cage. The cage is the “S” shaped construction that holds both jockey wheels and has the chain threaded through it. This is responsible for moving the chain back and forth across the gears, and is pushed back to take up the chain slack.

Derailleurs can be made of different materials depending on cost, weight and the specification of the bike. Steel is common, especially for front derailleurs, but aluminum alloy is by far the most popular. You can buy carbon derailleurs but they will have alloy or plastic jockey wheels for longevity.

Keeping the derailleurs clean and lubricated is one of the quickest maintenance tasks you can do on a bike, but it has the most profound effect. There’s nothing like noisy gears to put you off a ride so keep your Ultegra derailleur well maintained. 

Models

SRAM derailleurs are among the most reliable in the market,

Pricing

Derailleur pricing varies greatly across the range. A decent front derailleur from Shimano can cost from $20 for a Alivio up to $150 for Dura-Ace or XTR. Rears are much the same, with a Tourney model from $10 to the ATR at $280 or Dura-Ace for $300.