[KenWittlief]

if you dont like castors then the next best thing is to have steerable wheels, like a car or wagon.

4 wheel drive with tank/skid steer is hidious - the amount of power and energy you waste dragging a drivewheel sideway is tremendous - in this years game, as other have pointed out, if you dont want to use castors, use a couple blocks of nylon instead, and have most of your weight balanced over your drive wheels.