A fixed differential gear system. This arrangement has a typical ratio of between 15:1 and 100:1. The ratio is given by:

${\displaystyle m_{G}={\frac {N_{R2}N_{P1}}{N_{R2}N_{P1}-N_{R1}N_{P2}}}}$

where:

${\displaystyle N_{R1}}$ is the number of teeth on the No. 1 Ring gear (R1, yellow)

${\displaystyle N_{R2}}$ is the number of teeth on the No. 2 Ring gear (R2, green)

${\displaystyle N_{P1}}$ is the number of teeth on the No. 1 Planet gear (P1, dark blue, on the left)

${\displaystyle N_{S2}}$ is the number of teeth on the No. 2 Planet gear (P2, dark blue, on the right)