Shifters are controls that allow a cyclist to change cogs of the rear cassette on-the-fly, distributing power throughout a range of gears. This mechanism is actuated by tightening or loosening the tension on the shifter cable, raising or lowering the derailleur to the correct setting, guiding the chain onto the new selected gear. Most shifters have settings adjusted to locate the cogs immediately. This allows the rider to focus on riding, but it wasn't always that easy.
Shifters and assorted parts can be purchased online on the cheap. For around $20 you can find many types of low-end shifters (all but the integrated variety). Decent shifters with brand names start around $50, and from there the value increases linearly into the several hundreds of dollars.
Some specialized integrated shifters go for over $1,200 on Amazon.com.
Installing or repairing a shifter needs some focus. Making adjustments affects the entire system, and something very simple can lead to cable tension being different, or a misaligned derailleur.
First things first, remember that shifter cables are different than brake cables. There are new, more versatile housings being made, but as a rule they are not interchangeable. The stress of braking would snap a shifter cable. Shifting with a brake cable, much like walking a dog with a large wet noodle, would also lead to big problems.
Weather can wreak havoc on shifting components, so sometimes it's necessary to take apart the hardware and clean the rust and gunk. Don't be shy with degreasers and lubricants.
Regardless of the mechanism that actuates the shift (twist shifters, trigger, thumb, or flappy paddles), installation means mounting the shifter in a comfortable location on the bars and properly adjusting the cable. Most shifters clamp to the handlebars via pinch bolt (likely a phillips, 3mm, or 5mm hex).
For more information on cleaning, lubing, and installing shifters and cables, check out our tutorials below.
Bike handlebars come in many shapes and sizes and as such, so do the shifters mounted on them.
Friction shifters: Rear derailleur is held in place by friction of the cable and shifter. It falls on the rider to find the correct setting for each gear.