[Aren Siekmeier]

I don't get it. You obviously can't have both front wheels and both back wheels together, because both sides are always doing the same thing, and you therefore can't turn. Also, if you try to make the front wheels do something different from the back wheels, you will just shred your tread (at best).

You CAN however have each side on one gearbox, and as already stated many times, there's no reason not to. Standard tank turning is accomplished by running each side at different speeds (or even different directions).