Non U-bar Roll Bars

How does a manufacturer account for torsional rigidity in a bar which has kinks or bends? When deciding to go to a new bar, how can one calculate the difference needed to obtain the required results or verify that a manufacturer has taken this into account?

While they may calculate the result, they probably just test it. If you have a target bar rate, and it can be easily bench tested to verify the actual rate. Fine tuning is probably done with the arm length to the drop length.

As David said, it can be calculated - hopefully by CAD or somesuch as it would be a PITA to do it on paper as the tortional, twisting stiffness across the vehicle increases by the 4th power of the diameter, but the longitudinal links increase by the 2nd power - and there is a whole lot of sections where it will be a mixture of both.

Easiest thing, as David also said, is to try something that seems about right, from experience, and measure that and increase or decrease the diameter as required.

Because there's going to be differing stiffness rates throughout the bar, a rule of thumb when experimenting may be to use the 3rd power or, if you have the math, make 3 or 4 bars of different diameters, but the same shape, and calculate the correct power constant for that specific bar design.