I saw this video recently and find it surprising. Being a Carpenter, I have some basic engineering knowledge in terms of construction materials. I find it very strange that a hollow bar can provide greater strength than a solid bar. If this is actually true, why hasn't anyone made hollow torsion bars? I like the idea of weight savings. I'd consider one of these if I could hear from someone that could explain in basic terms why a hollow member is stronger than a solid one. Is it in the metallurgy?