[EricH]

Think of it this way:

Your center of gravity is right above your middle "dropped" wheel. (I don't much care how far up it is; that's your choice.) So far, so good, right? Now, you accelerate forwards. Your CG is a little bit slower than the drive frame to respond (law of inertia--it takes a little bit to get the motion up there), and you rock onto your back wheels. You'll stay there until you stop. When you stop (accelerating backwards), the CG again takes a bit to figure out, "Oh, I need to stop!" and goes into the front section. You rock onto your front wheels. The rebound sends you onto your back wheels. Repeat until the CG stops moving. But...

You may be moving again already, or you may be trying to acquire a game piece. This prevents the CG from settling. Worse, the CG bouncing around could potentially throw off your attempts to pick up the piece. In a typical game where speed in acquiring and unloading is important, this can adversely affect scoring potential.

Having the CG on one end or the other WILL NOT stop the rock. It will, however, make it settle much faster.

It's like a seesaw-- sure you can balance it on the middle. Give it a light tap, and it leaves the middle. So you have to work to return it to level. Add a little more board to one side to keep one end down, and you don't have to work as hard to return it.

Oh, and you can easily have a 6WD that turns without bouncing or drop. Stick omni wheels on one end.