Rear Shifting

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Cycle components - Rear shifting
The main job of a rear derailleur, or mech, is to convert cable motion into sideways displacement ie make the mech move the chain to a different sprocket.

The clicks are in the shifter and that is what determines the number of speeds, by pulling or releasing a certain amount of cable (and of course it has a corresponding number of clicks). The mech provides a conversion or shift ratio that is the same across road and mountain alike and regardless of how many speeds it says on the box. All that really indicates is how precisely the mech is constructed. More speeds mean a closer pitch and that demands more precision to avoid the chain rattling against the next sprocket.

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