where did you get that information? increase roll stiffness? a hollow tube is more susceptible to failure. for the same size diameter solid vs. a tube and the same amount of torque applied, the tube will have more torque applied to less material, giving the overall shear stress to be greater throughout the bar. the only thing beneficial of a tube is weight savings.If fitment or space is an issue than maybe we are barking up the wrong tree going after Racing Beat. Hotchkis is the only one I know that makes hollow bars. So here is a way to save weight and increase roll stiffness because a hollow tube ends up being twice the rate as a solid bar.
But who cares what size the bar is, as long as it performs better. Bigger is not always better.