School me on sway bars - hollow vs solid
 

At the autocross meet earlier this month a couple of competitors were having a discussion which I was just passively listening in on.
One was mentioning to the other that he can get a different sway bar and still stay in class and specifically mentioned that the best choice is a hollow front sway bar.

What (if any) are the practical advantages of the hollow sway bar?

Equal stiffness and less weight

What Pat said.

Torsion/Sway bar stiffness is proportional to the 4th power of the bar's diameter, and because of this the stress distribution is such that the outside of the bar is contributing dramatically more to the stiffness than the metal on the inside. The exact center of the bar is theoretically contributing nothing to the stiffness of the bar, but extra metal weighs more than air. Hollowing it out gets you most of the stiffness with a lot less weight.

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