Formula D₁ x N₁ = D₂ ÷ N₂

D₁ = Tail-Pulley diameter
N₁ = revolutions of driving pulley
D₂ = Drive-Pulley diameter
N₂ = revolutions of driven pulley


*Knowing the speed of the fan and tail-pulleys, want to know the size of the drive-pulley

Set :			- Fan Speed = 900 RPM - Tail-Pulley 8" - Drive-Pulley? - Motor 4P (1,400 RPM)
method :			=   D1 x N1   =   D2     N2         =   8" x 900   =   D2     1,400         =   7,200   =   D2     1,400         =   5.14 นิ้ว