There is so much wrong with this i have drawn a diagram for your benefit:
Situation A: you want to move your raider 12 inches straight forward. you pick a point on your tank (in this case the very front) you then measure twelve inches and then move said tank so that the same point (the front of the tank , is placed at the end of the tap measure or 12 inch mark depending on which way round your holding the measure)
Situation B: exactly the same except using a central point on the tank, you measure from this point and too this point.
Situation C: This is where you wish to pivot your tank. In this diagram i have included Situation A to show how you in-fact gain nothing by your technique of pivoting during the move and then returning to facing forward. heres a break down:
If you choose to pivot your raider, you lose two inches as your width is shorter than your length and you measure in the direction your traveling so from the side of the raider you move twelve forward then pivot back to facing forward re-gaining that two or so inches. so thats -2 (to start your move) +plus 12 during the move and then +2 from the pivot giving you a total of 12.
The same applies if you start your move say forward 6, then pivot, then sideways 6 then pivot again, because by pivoting you reduce the length of your vehicle.