Whether upshifting or downshifting, the bicycle derailleur system design requires that the drive chain be moving forward and be under at least some tension. A derailleur will shift only if you are pedaling forward.
1) Shifting the Rear Derailleur
The rear derailleur is controlled by the right shifter. The function of the rear derailleur is to move the drive chain from one gear to another on the rear gear cluster, thereby changing gear drive ratios. The smaller sprockets on the gear cluster produce higher gear ratios. Pedaling in the higher gears requires greater pedaling effort, but takes you a greater distance with each revolution of the pedal cranks. The larger sprockets produce lower gear ratios. Using them requires less pedaling effort, but takes you a shorter distance with each pedal crank revolution. Moving the chain from a smaller sprocket of the gear cluster to a larger sprocket results in a downshift. Moving the chain from a larger sprocket to a smaller sprocket results in an upshift. In order for the derailleur to disengage the chain from one sprocket and move it on to another, the chain must be moving forward (i.e. the rider must be pedaling forward).
2) Shifting the Front Derailleur:
The front derailleur, which is controlled by the left shifter, shifts the chain between the larger and smaller chainrings. Shifting the chain onto a smaller chainring makes pedaling easier (a downshift). Shifting to a larger chainring makes pedaling harder (an upshift).
b) Which gear should I be in?
The combination of largest rear, smallest front gears is for the steepest hills. The smallest rear, largest front combination is for the greatest speed. It is not necessary to shift gears in sequence. Instead, find the “start- ing gear” which is right for your level of ability
3. Shifting an internal gear hub drivetrain
If your bicycle has an internal gear hub drivetrain, the gear changing mechanism will consist of:
•a 3, 5, 7 or possibly 12 speed internal gear hub
•one, or sometimes two, shifters
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