[sanddrag]

Torque is directly proportional to current. For a certain motor, their will be a certain stall torque for which their is a stall current. The stall current for the FIRST drive motors is usually well above what the breakers can supply before tripping. So, you want to design your drive system around not tripping your breakers. When your motors are drawing about 40 amps, whatever torque they are making (determined by the curve graph), should translate through your drivetrain into (at least) just starting to make your wheels slip. Now, how much force does it take to make the wheels slip? Your guess is as good as mine. The main case in point is that you want the wheels to slip before the breakers trip.