Bicycle Derailleurs
Derailleurs (there are two, front and rear) are the devices that do the greatest work involved in shifting gears: that is, actually moving the chain from one sprocket to another. The rear derailleur (a French word; the Englishlooking things on the rear tire, called cogs, with the aid of two pulleys or wheels. The front derailleur deals with the bigger sprockets near the pedal, known as chainrings and which make the greater difference in performance when shifted.
So this pair of funny small things assures the smooth functioning of the chain, of speeds, of resistance. Unless you plan on adopting the Ironman philosophy of single make sure you're derailleurs are in good functioning order.
Why Change?
Many derailleurs will last as long as your bike. But you will want to change your derailleurs if you want upgraded performance. You can often lighter derailleurs to increase your speed or go for the latest technology that makes shifting gear completely seamless.
The most common reason to replace your derailleurs you broke the last one. The '''rear '''derailleur can be bent quite easily. When a bike falls over, rear "derailer" is the first victim to get bent. Before you go through the trouble of buying a new rear and replacing the old, make sure it's not just a bent hanger, which
clean and lube them regularly.
How to Choose
Buying a derailleur can be confusing. Aside from wrapping your head around the technical aspects of how they work, they're also built to specific measurements so you can pick a derailleur that works best for your bike. You'll need to select, based on your current drivetrain (the stuff that makes the bike go), including your current derailleurs:
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* The tooth capacity (the difference between your biggest and smallest chainrings) for your front derailleur, and
* Total capacity (the tooth difference between your biggest cog and smallest cog + capacity) for your rear derailleur.
Types of Derailleurs
Front Derailleurs
Deore derailleurs are also compatible with just about any other component (this is also true of Deore rear derailleurs).
'''Top Pull versus Bottom Pull''' Traditionally, front derailleurs are controlled by a "bottom pull" system, which requires the shifter cable run the length of the down tube and underneath the bottom bracket. Top-pull systems have their cables routed across the top tube and down the backside of the seat tube. The cable doesn't have to pass near the bottom bracket at all. There are two advantages to the top pull system:
* With bottom-pull routing, dirt, mud and various other debris get caught in the cable under the bottom bracket shell. This is especially true of mountain bikes.
* The shorter the distance from shifter to derailleur, the quicker the shift and faster the response.
* Check the cable stays on your bike frame to see if top pull systems will work for you.
Rear Derailleurs
Like front derailleurs, rear derailleurs also have a capacity measurement, though with rear derailleurs it's known as "total capacity" or "chain wrap." This is the sum of the capacity (difference between the largest and smallest chainring) and the difference between the largest and smallest cogs in the back. So, if your cogs range from 15 to 26 teeth, the difference would be 11 tooth leeway.
'''Long Cage versus Short Cage''' The essential difference between rear derailleurs is cage length. The cage is the rectangular metal bit that houses the two pulleys, the top pulley (known as the guide or jockey pulley because it guides the chain through the cage) and the bottom pulley (known as a tensioner or idler pulley because it maintains chain tension as you shift, taking up the chain slack). The cage comes in three sizes: short, medium and long.
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Short cage derailleurs are most often used with road bikes that use double
cranksets (meaning they have no need for the smallest chainring) and will keep your chain tighter than a longer cage.
** Downhill and freeride mountain bikers will often use short cage derailleurs because of the ground clearance and ability to keep the chain tight.
** Disadvantages: Short cage derailleurs will have trouble working with cogs with more than 26 tooth (on road cassettes) or 28 tooth (on MTBs).
Major Manufacturers
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Bianchi
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Campagnolo
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Shimano
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Sram
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Tourney
Reliable Picks
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