Bicycle cog? Doesn't sound right. Alternator sprocket? Doesn't sound right. Not saying anything is wrong technically, just doesn't sound right. Bicycle sprocket, alternator pulley sounds right.
gear
1 of 2
a(1)
: a mechanism that performs a specific function in a complete machine
steering gear
(2)
: a toothed wheel
(3)
: working relation, position, order, or adjustment
got her career in gear
(4)
: a level or pace of functioning
kicked their performance into high gear
b
: one of two or more adjustments of a transmission (as of a bicycle or motor vehicle) that etermine mechanical advantage, relative speed, and direction of travel