Compound Gear Train:

In this kind of gear train, two gears are mounted on the similar shaft and they rotate at the similar speed. This gear train is illustrated in given Figure where gears 2 and 3 are mounted on similar shaft and they rotate at the similar speed, that means

                       N₂  = N₃

Compound Gear Train

Assume N₁, N₂, N₃, . . . is speed in rpm of gears 1, 2, 3, 4. . . , etc. and t₁, t₂, t₃, . . . , etc. be number of teeth of respective gears 1, 2, 3, 4. . . , etc.

Gear Ratio =

Thus, unlike simple gear train the gear ratio is contributed by all of the gears.