A set of rear sprockets (also known as a cassette) running. Most bikes have two or three chainrings, and between 5 and 11 sprockets on the back, with the number of theoretical gears calculated by multiplying front by back. In reality, many gears overlap or require the chain to run diagonally, so the number of usable gears is fewer. Different gears and ranges of gears are appropriate for different people and styles of cycling.