Heavy vehicles exhibit limited directional performance and stability limits due to their large dimensions and weights. The liquid tankers are among the freight vehicles with relatively lower stability limits due to the special condition of their cargo that tends to shift in the longitudinal and lateral planes under braking/acceleration and turning maneuvers, when partly-filled. The objective of the present work is to derive an optimal geometry of the cargo tank to enhance the direction performance of the partly-filled vehicle combination during braking/acceleration and turning maneuvers. An optimal longitudinal section of the tank is identified to reduce the fore-aft load shift encountered during braking maneuvers. The identified geometry is coupled with an optimal lateral section, reported in the literature, to synthesize the tank that would yield reduced load shifts in the lateral as well as longitudinal planes