Originally Posted by Red-Stripe
It's all about proportions.
4WD drives all 4 wheels despite what some post here.
Unlocked diffs are equal torque designs, so if the friction and weight under your tire are close: you get the same power to all 4 wheels.
Think of it this way: Neither opposing wheel can receive more torque from the vehicle than it's connected opposing wheel. So if one rear wheel is on asphalt, and the other is on ice, the one on asphalt can not receive any more torque than the one on ice. Normal 4WD works so well, because the vehicle is moving and the weight loading on the wheels is constantly changing, giving the 4 wheels the "average" of the friction limit.
That's the point of lockers and LSDs...for when the friction and weight under the tires isn't close.
That has got to be the worst discription ever of an open diff and 4wd.