So there seems to be alot talk about Ball vs Gear lately and I wanted to post this from AE's r/c handbook just for knowledge of fellow peeps.

Differential
Your buggy or truck gearbox (transmission) is fitted with a differential. The purpose of the differential is to let the wheels turn at slightly different speeds. This is necessary to help the car turn corners. When you car turns a corner, the outside wheel has to travel further than the inside
wheel, thus it needs to turn slightly faster to keep up. Differentials (or diffs) in model cars are typical of two kinds. Entry-level cars (from companies such as Tamiya or Kyosho) often use ‘gear diffs’ while more competition oriented manufacturers use ‘ball diffs’. Both work in the same way, and largely achieve the same thing.

Ball diffs, however, are slightly adjustable. By slightly increasing or decreasing the tension on the diff screw (see your instruction manual for details on how) you can make the diff ‘looser’ or ‘tighter.’ A tighter diff is one that is hard to turn. Tighter diffs help your car to put down power coming out of
corners and in a straight line, while looser diffs help your car to turn corners better. If you loosen the diff too far, it will allow the diff to slip, which is a bad thing. Diff slip damages the components of the diff and is inconsistent. Your instruction manual will describe how to tell if your diff is slipping or
not. I never recommend running any diff slip, because that’s what a slipper clutch is for.