Different cycles are fitted with different shifters due to the constraints of cost and functionality. In general bicycles gear shifters are classified into 3 categories. They are:
Mountain Bikes and Hybrids are generally equipped with Thumb Shifters. This type of shifter is generally installed on straight handlebar cycles, right next to the brake levers. The location of the thumb shifter actually differs across the cycle range. In some cycles the shifters are located on top of the handlebar whereas in other models, they are found on the underside of the bar for better ergonomics. When the cyclist operates the shifter, each click on the same corresponds to a different gear on the drivetrain. These days, cycles with Thumb Shifters have a second lever on top, which allows the rider to shift using his/her index finger. Thumb Shifters may or may not be attached to the brake lever. If they are not attached, they can be removed separately for repairs.
Twist Grip Shifters
This type of shifter is generally found in entry-level multi-geared cycles. The shifter is integrated with the handlebar’s grip on one side or on both sides. The twist grip shifter is only installed in straight handle bar cycles. The rider upshifts or downshifts by twisting his/her hand in either direction. Due to the fact that the shifter is right next to the grip, the rider can shift conveniently without having to move his/her hands. One minor issue with the twist grip shifter is that gears tend to slip out of place sometimes. Maintenance of twist grip shifters is also slightly tricky and time consuming because they are integrated into the handle bar.
Dropbar Integrated Combo Shifters
The Integrated Combo Shifter is exclusive to Road Bicycles with drop down handlebars. This shifter is so named because the brake lever and the gear shifter are integrated into one piece. This allows for quick and convenient shifts that reduce the overall shifting time. The Integrated Combo Shifter is light weight as well. The shift lever is located behind the brake lever. The construction is such that the shift lever and the brake lever’s motion is independent of each other. This type of gear shifter is relatively more expensive than the other types. Also, due to its complex construction, it is very difficult to find spares for the individual parts. This makes maintenance a hassle as the entire shifter has to be replaced.