Are the lower gears big or small?

Answer 1

A gear is always made up of (at least) two sprockets (or cogwheels), and the only size that matters is size in comparison, and which is input and which is output. This is also known as a ratio

For a bike input would be by the crank and outputwould be by the rear wheel.

You get a lower gear by making the input smaller and/or the output bigger, and you get a higher gear by making the input bigger and/or the output smaller.

Answer 2

On an automobile differential (one of the categories you chose) the small gear is usually the input gear. On a bicycle the large sprocket is the input "gear" usually.

However, whether the gear is an input or output gear has nothing to do with size, but the location. The gear connected to the power source (engine, motor, or pedal crank) is the input or driving gear. The output or driven gear is the one connected closest to the wheel(s) or whatever is being turned (such as the drill chuck on a drill press).

So on a bicycle, the front crank is the input gear and the freewheel sprocket assembly on the rear wheel is the output gear. On a drill press, the pulley on the motor would be the input and the pulley driving the chuck would be the output. However, They often us an additional idler pulley and two belts. So the idler pulley is the output in relation the motor, but the input in relation to the chuck.