I just bought some used S-Runner anti-sway bars to put on my truck, thanks AFP520!!
I was wondering how much stiffer the new bars will be so I did some calculations. For those that don't care about the calculations, jump to the bottom of this post for the result.
S-Runner bar diameter:
27.7mm front
22.2mm rear
My truck's bar diameter:
27.0mm front
No stock rear bar, but the Hellwig bar is 19.2mm
I was thinking the front bar wouldn't be too much stiffer, however I recalled from long ago engineering shool that in the equation that was needed, the bar diameter is raised to the 4th power. Therefore a small change in diameter makes a big change in torsional stiffness.
Here is the equation:
k=GJ/L
k=spring rate of the bar
L=length of the bar
G=Modulus of Rigidity of the material
J=polar 2nd moment of inertia (depends on the material shape)
in the case of a solid round bar, J=(pi*d^4)/32
Therefore k=(G*pi*d^4)/(32*L)
Assumptions
1) The material in all the bars is the same. This is a safe bet for the OEM bars, and I believe the Hellwig bar is also spring steel (Addco bars are supposedly not spring steel, so G will be lower for those bars, so they aren't as stiff as you think).
2) The lengths are nearly identical, s-run front bar vs. 2wd front bar, and s-run rear bar vs. hellwig rear bar; good assumption for the two OEM front bars, but not so good for the S-runner rear bar compared to the Hellwig bar, but close enough for me.
3) My measurements are accurate. The paint on the bars is pretty thick, so my numbers could be off if the paint thickness varies from one bar to the other, and small numbers make a big difference in this calculation.
So I end up with an equation where the only difference from old bar vs. the new is the bar diameter, which is raised to the 4th power.
Result (trust me):
S-Runner front bar is 11% stiffer than my OEM bar (may not be noticeable)
S-Runner rear bar is 79% stiffer than the Hellwig bar and infinitely stiffer than stock!!
It's gonna be a while before I get the rear bar mounted, since I need to figure out how to mount it to the rear axle housing.
I was wondering how much stiffer the new bars will be so I did some calculations. For those that don't care about the calculations, jump to the bottom of this post for the result.
S-Runner bar diameter:
27.7mm front
22.2mm rear
My truck's bar diameter:
27.0mm front
No stock rear bar, but the Hellwig bar is 19.2mm
I was thinking the front bar wouldn't be too much stiffer, however I recalled from long ago engineering shool that in the equation that was needed, the bar diameter is raised to the 4th power. Therefore a small change in diameter makes a big change in torsional stiffness.
Here is the equation:
k=GJ/L
k=spring rate of the bar
L=length of the bar
G=Modulus of Rigidity of the material
J=polar 2nd moment of inertia (depends on the material shape)
in the case of a solid round bar, J=(pi*d^4)/32
Therefore k=(G*pi*d^4)/(32*L)
Assumptions
1) The material in all the bars is the same. This is a safe bet for the OEM bars, and I believe the Hellwig bar is also spring steel (Addco bars are supposedly not spring steel, so G will be lower for those bars, so they aren't as stiff as you think).
2) The lengths are nearly identical, s-run front bar vs. 2wd front bar, and s-run rear bar vs. hellwig rear bar; good assumption for the two OEM front bars, but not so good for the S-runner rear bar compared to the Hellwig bar, but close enough for me.
3) My measurements are accurate. The paint on the bars is pretty thick, so my numbers could be off if the paint thickness varies from one bar to the other, and small numbers make a big difference in this calculation.
So I end up with an equation where the only difference from old bar vs. the new is the bar diameter, which is raised to the 4th power.
Result (trust me):
S-Runner front bar is 11% stiffer than my OEM bar (may not be noticeable)
S-Runner rear bar is 79% stiffer than the Hellwig bar and infinitely stiffer than stock!!
It's gonna be a while before I get the rear bar mounted, since I need to figure out how to mount it to the rear axle housing.