Like, on a mountainbike you have two levers, one for the index finger and one for the thumb. why does on the right side the index give a “harder” gear and on the left the index finger lever give a “easier” gear? couldn’t they both give high and low gear in the same direction?
In: Engineering
The thumb moves the chain to a larger gear and the index finger to a smaller gear. That has the opposite effect on the pedal versus the wheel sprocket.
The question of why that setup. One reason is to move the change to a large sprocket you push the chain against the larger sprocket to force it to jump up. The motion extends the chain and is again the chain tension system. The required force to move to a smaller gear is just to pull the chain off a gear into the air so the tension mechanism pulls it tighter and to the smaller gear.
There is inherently less force required to move to a smaller than a larger gear so the springs in the gear shift system are set up to move the chain to the smaller gear.
Your thumb can apply move force the your index finger so it is used to pull against the spring and apply enough force to move the change to a larger gear. Your index finger just loosens the locking mechanism and lets it jump to another-looking position.
With good gears where not a lot of force is required, you can have a setup where the index finger increases the tension of the wire. They are just not as common.
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