Anautomatic transmission iscomposed of a wholetwo planetary gearcombination. From left to right:circletoothRINGwheelGEAR,theplanetcarrierPLANETCARRIER,and twosunteeththe SUNGEARS Anyplanetary gearhas threeimportant components: Sun gear Planetary gearandtheplanetary gearcarrier Circletooth Eachpartcanchangetheinput,output,orstill.Select a different combination,you can geta differentgear ratio. This casea set of gearswithoutandtheother gearassociatedseparatedcan be outputtoa different gear ratio.Thetwo sets ofgearlined upfour forward gears andone reverse gear.