Mountain bike gear levers control the position of your front and rear derailleurs, which in turn control the gear in which you are pedaling. The controlling link between your handlebar gear lever and your derailleur is the shifter cable, which changes the amount the derailleur is pulled to one direction or the other, lining it up with a smaller or larger sprocket or chain ring.
Control
The left gear lever on your handlebars controls the front derailleur, and the right gear lever controls the rear derailleur. You push or pull the gear-shifting lever with your thumb or fingers. Pushing the lever "up," or away from, you shifts the chain to a higher, more difficult gear. Smaller sprockets are higher gears on the rear wheel, and larger chain rings are higher gears in the front.
Cable Attachment
The shifter cable has an end piece, usually shaped like a cylinder, which hooks into an indentation inside the lever so it will not pop out. The cable runs out through a hole on the base of the lever and into a protective tube called cable housing. An adjustable tension screw, also called a barrel adjuster, is normally present just outside of the lever. Unscrewing it pulls the cable tighter by lengthening the distance it must stretch, while screwing it in releases tension on the cable.
Frame Attachment
The cable runs along or inside the frame of the bike, protected entirely or at specific points by cable housing. Cable housing also directs the cable in directions that it would not normally go if controlled only by tension. Cable stops also direct the cable by providing a socket for the housing and keeping it close to your bike.
Derailleur Attachment
The derailleurs attach to the bicycle frame with nuts and bolts. Your front derailleur attaches to the seat tube, and your rear derailleur attaches to or just above the wheel dropouts. Where the cable reaches the front derailleur, it exits or has already exited the cable housing and is secured in place by a clamp, nut and bolt. Where the cable reaches the rear derailleur, it exits the cable housing, passes through another adjustable tension screw and is held in a clamp fastened with a nut and bolt.
Derailleur Operation
When you're riding, as you push the gear lever up, the tension in the cable increases. For the front derailleur, this pulls the spring-loaded chain guide, called a cage, out toward the larger chain ring. The chain begins to run at an angle over the chain ring, and when the cage is in line with the next chain ring, the chain moves. Mountain bike rear derailleurs often operate the opposite way, with the cable tension pulling the derailleur toward the lower gears and larger sprockets. The rear derailleur includes a pair of pulleys inside its cage, which help rotate the chain around the sprockets and back toward the front chain ring. Pulling either gear lever toward you decreases cable tension and moves the derailleur cage to the left and to lower gears.
Member Comments