Derailleurs
The derailleur is the device that changes gears by moving the chain from one sprocket to another. There are two derailleurs: one on the rear and one on the front. The highest ratio (when the bike can go fastest) is produced when the chain is on the biggest sprocket in the front and the smallest in back. The lowest ratio (the bike is easiest to pedal up hills, but very slow) is produced when the chain is on the smallest sprocket in front and the biggest in back.
Shimano SLX M661 Mountain Bike Front Derailleur 34.9mm
$23.99 
Time Left: 4h 9m | |
| Shimano LX M580 Mountain Bike Front Derailleur - 34.9mm
$15.19
Time Left: 4h 10m | |
| Shimano LX M581 Mountain Bike Front Derailleur - 34.9mm
$15.19
Time Left: 4h 10m | |
| Shimano XT M770 34.9mm Mountain Bike Front Derailleur
$39.99
Time Left: 4h 10m | |
| SHIMANO SLX FD-M661 MOUNTAIN BIKE FRONT DERAILLEUR NEW
$37.87
Time Left: 5h 11m | |
| Sram X-9 X9 Mountain Bike 9 Speed Rear Derailleur
$58.87
Time Left: 22h 20m | |
| Mountain BMX Bike Bicycle Frame Chainstay Protector Pad
$2.99
Time Left: 1d 4h 27m | |
| SHIMANO ALTUS REAR DERAILLER MOUNTAIN COMFORT BIKE
$15.00
Time Left: 1d 7h 8m | |
| SHIMANO ACERA 8 SPEED REAR DERAILLER MOUNTAIN BIKE NEW
$20.00
Time Left: 1d 7h 13m | |
| SHIMANO SLX FD-M661 MOUNTAIN BIKE FRONT DERAILLEUR NEW
$37.87
Time Left: 1d 7h 54m | |
| Shimano LX M580 Mountain Bike Front Derailleur - 34.9mm
$6.99 (0 Bids) Time Left: 1d 8h 34m | |
| Shimano XT M770 34.9mm Mountain Bike Front Derailleur
$16.28 (3 Bids) Time Left: 1d 8h 34m |
In general, a derailleur is a mechanical means for moving the bicycle's chain from one cog to an adjacent cog, of a different size, so as to change the gearing of the bicycle. Bicycles equipped with derailleurs and multiple cogs - typically a group on the rear hub, and another group on the pedal crankset - allow for changing the gearing while the bicycle is in motion, which means that the rider can adjust the 'ease of pedaling' to suit the load being carried/pulled, to suit the immediate terrain, or to accommodate for other factors such as a headwind or the surface on which the bicycle is being ridden.
