The suspension roll motion can produce roll steer, which are functions of roll angle, thus producing extra lateral forces. This paper develops the total variance approach to analyze the effect of suspension roll on commercial vehicle handling dynamics. The side-slip angle unified transfer function, reaction time, transition time, damping ratio and total variance are introduced with the effect of suspension. The vehicle designers could use this approach to get optimization design parameters of vehicle without numerical calculation. For the two-axle commercial vehicles, the total variance approach is useful and could serve as an important tool for evaluating the effect of vehicle suspension roll on commercial vehicle dynamics.