Many difficulty levels and body positions need to be accommodated in bicycling, and this has brought several types of shifters to the market. Mountain biking and road cycling exhibit the largest differences in style and location of shifters. The types of shifters may also vary depending on the era in which each was produced as each decade has seen many popular shifter designs. Functionality and cost also impact the style of bicycle shifter a person may use.
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The thumb shifter is the most common type of shifter found on mountain bikes. They are installed on the straight handlebar next to the brake levers. Some thumb shifters are located on top of the bar, while newer models are fitted on the underside of the bar for location convenience. Generic replacement models are usually friction based shifters, where the rider must manually adjust the cable tension to shift up or down. Newer models have indexed slots with each shifting click corresponding to a specific gear on the drivetrain. Newer index thumb shifters also have a second lever for shifting with the index finger. Some thumb shifters come integrated with the brake lever and may be permanently attached while others can be removed for repairs.
Twist Grip Shifters
The twist grip shifters are a relatively new design in the evolution of changing gears. The twist grip mounts on straight bars and blends in with the standard handlebar grip. The rider simply twists his hand toward or away from him in order to shift up or down. One main advantage to this style is that the rider has immediate access to shifting without having to move his hands to a new location. The downside is that the indexed shifting slots easily become rounded and worn and the gears may slip out of place. The Barnett Bicycle Institute states that because twist grip shifters are integrated onto the bar, their maintenance may be more difficult and time consuming.
Dropbar Integrated Combo Shifters
The road bike combo brake and shift lever is the newest model in the evolution of bicycle shifters. On the curved road style handlebar, the brake lever and shifter are integrated into one streamlined piece that reduces overall weight and shifting time. The shift lever sits directly behind the brake lever, while both levers move independent from each other and will not interfere with each other's functioning. The Park Tool website states that each brand of combo shifters must be fitted to their exact corresponding derailleurs and gear sets. One of the drawbacks to this style of shifter is that it uses complex and highly specific parts that are not interchangeable with other brands or even past models. If one part of the shifter brakes, the whole component must be replaced.
Other models are mounted on the stem, downtube and bar ends. Stem shifters are often found on older road bikes, are made of simple metal parts and use the friction system rather than indexing. Downtube shifters mount on the downtube of road bikes and are designed to reduce the amount of cables and housing used. Bicycles with downtube shifters have a more streamlined look but require the rider to reach down in order to shift gears. Bar end shifters mount on road bars and insert directly into the end of the bar. This style allows the rider to ride with her hands in the racing position at the end of the handlebar, with shifting taking precedence over braking.