What is the name of the front gear in a bicycle drivetrain?

The front gear in a bicycle drivetrain is called a chainring.

A chainring is a toothed wheel attached to the bicycle’s crankset, the assembly turned by the pedals. As the rider pushes the pedals, the chainring pulls the chain, transferring power toward the rear wheel. Bicycles may have one, two, or three chainrings, although modern drivetrains often use one or two.

The main mix-up is with the cassette or sprocket. Those toothed gears sit at the rear wheel; the chainring is at the front. A derailleur is not a gear at all: it is the mechanism that moves the chain between chainrings or rear sprockets. The number of possible gear combinations comes from multiplying the front chainrings by the rear sprockets, though some combinations overlap or are inefficient because of chain angle.

Chainrings are commonly identified by tooth count, such as 50 or 34 teeth. A larger chainring produces a harder, faster gear, while a smaller one makes climbing easier.