i=n1/n2=D2/D1 ,i=n1/n2=z2/z1. i represents transmission ratio or gear ratio n1 represents the speed of drive gear n2 represents the speed of driven gear D2 represents the diameter of driven gea i=n1/n2=D2/D1 ,i=n1/n2=z2/z1. i represents transmission ratio or gear ratio n1 represents the speed of drive gear n2 represents the speed of driven gear D2 represents the diameter of driven gea