How Do Bicycle Shifters Work?

Close-up of bicycle gears

Shifters can seem intimidating, but when reduced to the basics they are nothing more than levers, cables, springs and gears. Bicycle shifters are self-contained and need no power source other than your hands to operate. Simplicity is the beauty of bike shifters even though the technology that operates them is highly engineered. Once you grasp the concept of the bike shifter, it becomes easier to operate.

Shift Levers

When you pull or push on a shifter lever with your fingers or thumb, you hear the familiar click that means the bike has shifted. The click is the indexing feature on the shifter. Each time the lever clicks, it has selected another gear. Indexing means that the shift lever will not over shift, or under shift the bike. It has been calibrated to move the derailleur just enough to the left or right to lift or drop the chain exactly one gear at a time. The shift lever works under tension from the cable that runs from the lever, down the bike to the derailleur.


Cables under tension operate the derailleurs. Cables hold the derailleur in place directly over the gear according to the indexed position of the shift lever. When you click the shift lever -- depending on what lever you choose -- it pulls or adds slack to the tension on the cable. This allows the derailleur to move to the left or right and stop the chain on the correct gear according to the indexed position of the shifter lever. If you click the lever successively, the cable will continue to loosen or tighten, moving the derailleur over one gear for each click until it reaches the end of the gear stack and then it will stop no matter how many times you continue to click the lever.


The chain is moved to different gears by the derailleur. The derailleur has large springs inside that apply tension to the cables. When you push or pull the shift levers, it tightens or relives tension on the spring. Springs are the reason that your cables stay tight. When you push the shifter lever to shift to bigger gears, you will feel the resistance in the lever. This is the spring as it is stretched tighter. When you push the other shifter lever, you will hear it pop as the spring pulls back, moving the chain to a smaller gear. The derailleur moves back and forth on swivels. As the cable pulls the spring, the derailleur pivots on the swivel to move the chain to the correct gear according to the indexed position on the shifter handle.


Gears can sometimes be confusing. They seem to operate backward from each other from front to back. This makes the shifters appear to also operate backward from each other. For example; the largest gear on the front is the fastest gear used for cruising, but the largest gear in the back is the slowest gear used for climbing. Shifting a mountain bike takes some getting accustomed to, and even experienced mountain bikers shift the bike in the wrong direction occasionally. If you get confused about what gear you are in, it's OK to glance down at the chain and check. Or, if you are busy operating the bike, and you feel it respond with the opposite reaction to what you had in mind, click the shifter handles rapidly three or four times as fast as possible to move the chain in the opposite direction until you feel the pedals respond in kind.