Your tractive effort TE must just exceed the limiting friction on the driven axles. Then you must ensure that there is sufficient tractive effort to evercome the rolling resistance and gradient resistance. Wind resistance is not usually considered for plant.

TE is motor torque multiplied by the overall gear ratio & divided by the wheel rolling radius.

Then you plot the tractive effort against road speed to produce cascade curves which indicate the vehicle's performance in sympathy with the motor's speed/torque characteristic. There should be a separate curve for each gear ratio on the main cascade curve plot with overlaps during the hot shifting of automatic boxes. Don't forget the retardation!

Good luck. ■