Stan - these are hollow bars.....nothing like a 28mm solid!!
Not so,
being hollow does not significantly reduce their mechanical effect, it simply reduces the weight. The stock bar weighs 6lb, the RB tubular weighs 5.5lb. A 28mm solid bar would weigh around 14lbs.
Since a sway bar is essentially a torsion spring, it works on the resistance of the bar to twisting. The amount of resistance to twisting is governed by the diameter of the bar, and the effectiveness of that resistance increases the closer you get to the outer edge of the bar circumference.
Think long spanner compared to short spanner.
This is wrapped up by the area moment of inertia, or second moment of area.
I = (piDxDxDxDxD)/64
And can also be expressed as the polar moment of inertia.
J = (piDxDxDxDxD)/32
Which boils down to the larger the diameter, the more inertia. If you run a comparison from 0 to 28mm, you will see that at 14mm, I is 1885, at 28mm, I is 30,171. This is 16 times more resistance. Thus the inner 50% of a torsion bar does almost nothing compared to the effect of the outer 50%.
To get the total resistance of the bar, you seek the area under the curve from 0 to 28 for a solid bar and the inner dia to the outer dia for a hollow bar. For 0-28mm, a comparitive total is 184407, for 14-28mm 180025. So for not including the inner 14mm, you get 97% of the strength.
This is why when you go up in sway bar size, the effect of a 1mm increase is a substantially larger increase in stiffness.
After regurgitating that series of basic mechanical engineering from deep in my brain, i am off for a LLD (little lie down).
