Originally Posted by mugenblacky16

First of all, it's not dynamics because swaybars are fighting a bending moment and torsion and the sum of all those forces is zero. Second, what do you mean, "wall thickness is not an issue"? Of course it's an issue. Your graph is just a picture of the shear load distribution. It doesn't mean ----! Torsion applied to a tube is calculated different to factor that the tube has much less cross sectional area, not to mention that tau average is way out at the mean radius. A solid bar with a torsion applied has a bigger cross section. For example, to find the max shear stress(tau) in a solid shaft you would simple find the polar moment of
inertia( J=pi/2(r)4 ) and calculate to torsion formula (Jmax = Tc/J ). Tau max units are given in force/size; i.e. lb.ft. Tubular torsion uses the same torsion formula, but J will = pi/2(ro4 - ri4), which gives you the cross sectional area of the tubing wall.

The tubing used doesn’t need to be tempered. Without getting too involved use same dynamic equations to figure out how much force the bodyroll will have in a given turn on at a given speed minus the pressure of the force of the spring(stiffer springs will lessen the force on the swaybars). You’re trying to find how much force is lifting up on the car’s inside(side on the inside of the corner) suspension. Take that force(sigma or n) and times it by the distance from the point the swaybar and control arm link to the point where the sway is parallel with the firewall(heading to the other side) (d ). Measure 90° back. This will give you your bending moment and torsion back at where the swaybar heads to the other side.

Calculated sigma max of your tubes bending moment and cross check that the tension and compression are this in the elastic region of the material you are using (modules tables for specific materials can be found on the web or in the back of your statics and mechanics books). Next, cross check that the torsion does not exceed the elastic zone. If you forces are so great that they enter the yielding or even the strain hardening zone then the stress on the bar is too much and the swaybar will permanently deform. Bigger, thicker, stronger(material used) will give you a higher moment of inertia and handle more torque(from bodyroll forces). Just like everything you have to do you homework to do it right. Homemade swaybars are definitely possible and would probably work well, but expensive namebrand bars are expensive for a reason. They give you functional performance in a perfect balance. If you don’t want to do all the math I would try and copy the specs of a namebrand bar and find a material that has the same or as close to the same elastic region on the stress-strain diagram.