you sure about that… torsional stiffness is typically a constant. 0,0 intercept… So you can make a solid bar behave in exactly the same manner as a hollow bar… it’s just a matter of cross section design… But you aren’t going to get it to behave as anything other than a linear spring… however, like i said before, this is strictly for torsion… bending is another story. A hollow bar will be “stronger”, but from a performance standpoint, they are more or less alike…