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A gear ratio is the relationship between the number of teeth on two gears that are connected.

Gear ratio is the number of teeth on the following gear divided by the number of teeth on the driving gear (the gear inputting the motion).

A low gear ratio = more speed = less force

A high gear ratio = less speed = more force


Look at the gears in the diagrams below. 
gears



There are 18 teeth on the driver gear and 8 on the follower gear. The gear ratio would be 8/18 or 4/9. For every 4 turns of the driver, the follower turns 9 times.
gears If the gear and driver are switched. The gear ratio increases. The gear ratio would now be 18/8 or 9/4. For every 9 turns of the driver the follower will make 4 complete rotations.

This gear design would be good for multiplying force, not speed.