the way I understand it is, the heavier the oil less the diffs slip....basically meaning if you put thick oil in the front your rc would want to hop due to the the inside tire going into a turn is rolling faster then the outside tire...with the center diff you can control how much power your putting to the front wheels by using thicker or thinner oil...the thicker you use the more equal power you get from front to rear...the rear diff is pretty much the same as the front...the thicker oil you use the more equal the power is to each wheel