Sway Bar Spring Rates and Calculations

Al (Blizazer) was trying to decide if he should go back with the stock Blazer bar (33mm) or keep his Helwig (1.25").  The only real determination we were planning on using was the higher spring rate, but my quick google search really didn't turn up much of value since the two bars are made from different materials.  Obviously a thicker bar of the same material will have a higher rate and control the sway better, but like I said that isn't the case here.

Anyway I dug into google and found a couple good resources that I liked.

A good simple overview that was easily understood I found here:

Swaybar Design
By Scott Mueller

He doesn't go into the material portion, but it definitely helped me wrap my head around the concepts.

And then the all out mathematical equatiosn I found here:

Sway Bar Calculations by Michael J. Iacchei

From that I can determine that all things similar the diameter, shear modulus and elastic modulus are the primary contributors to the spring rate of a sway bar.

Still digging for a good source for the modulus.

We're going to have to know not only the type of material, but the grade as well before we can say for certain. I can say however, that a chromoly bar, like the helwig, is the better choice, from my side by side comparisons, on vehicles, the chromoly isn't noticeably stiffer, but it controls rocking and snaps back to flat better and faster. The corner exit is notably quicker and smoother.

The "ZQ8" bar on the S10 seems to give me the same feeling.  At least in the winter it puts the truck straight again with just a gentle flick of the wheel.

I can tell drop a bunch of info on the stock bar material once I'm back at work tomorrow.  IIRC it is heat treated SAE 1090 spring steel that is air cooled during the annealing process.  They also gave a hardness and grain size spec 

Only info I know on the Helwig is from their site.  4140 Chromolly.

How wide are to 2wd bars? I ask because I've found everything from 1.125" up to 1.5" adjustable rate sway bars.

stock bars are 1 1/8" IIRC, thickness (diameter)

If you find any more 1.5 inch bars or any adjustable bars scoop them up, they're not a stock item so worst case you could resell them for a lot more than any yard is going to get from you.

math is stupid. just hang a weight and measure deflection. even better if you can measure force transferred to get an idea of the efficiency too (probably not great)

perfect time to make use of your project frame.

rig frame securely to steel table, jig one control arm with scale under balljoint (cinder block with scale on it below balljoint. <-- this is at ride height arm angle

install swaybar.

hang weights off other side control arm balljoint.

measure deflection at weighted balljoint. take note of mass used and force the other side scale reads. do this at multiple masses.
plug into excel, matlab, whatever you want.

output aux spring rate and efficiency.

repeat for other swaybar.

obviously leave shocks and springs off for this test

Done!

How wide are to 2wd bars? I ask because I've found everything from 1.125" up to 1.5" adjustable rate sway bars.

Here is a listing of all the different stock sway bars, diameters, and vehicles they came on.  I did the research for it and can say it is quite accurate.

http://protourings10.com/index.php?topic=75.0

Ryo, I actually was thinking that direction would be much more accurate, but was trying to turn up some numbers without going through the effort, since I was trying to make a quick sale of the bar Al didn't want.  Took too long anyway and missed out on the sale, so I may just end up doing that since the the frame is ready for such a test.  No springs or shocks at the moment.  Just need to finish bolting the driver side back together.

For everybodies information here is the material called out for the stock sway.  Would be interesting to see how close calculations could come to the tested rate.

Steel Forging SAE 1090 Modified (Manganese 0.8-1.1%, Grain Size ASTM 5-8)
Heat treat by controled air cooling from forging temperature to obtain surface and core hardness of 302-363 HB.

mild steel huh, id be suprised if the calcs are within 20% of actual, based on how nonideal the geometry is

Hmm, testing you say.

We do have 2 33mm bars on hand, we could see what the variation between the two is.

what was the manufacturing method for these stock bars?
cast into shape then holes punched? cast with holes?
im just assuming cast. no bending

If they are made out of spring steel, I'm guessing they start out with a 33mm steel stock, heat it, and put it in to a die or a jig. If you notice the end links on most sway bars, the are a welded on piece.

Harley, I was actually asking how wide (end link to end link) are the 2wd s10 bars. But, after looking around, i found out that these adjustable rate bars are a different shape than the stock 2wd bars.

Artos, or Harley, maybe both of you would know, but Check out the options on this page

http://www.howeracing.com/c-511-stabilizer-anti-sway-bars.aspx

Go in to the 93 and up adjustable rate bars (3 thicknesses), original design sway bars (3 thicknesses), and then the mack daddy of them all the splined bar. the original design bars look like they could work on a 2wd s10. The splined bar has a shit load of combinations to make it work.

(From Howe website)
Allows you to run a splined sway bar on a offset Howe chassis. This splined sway bar assembly will fit Howe XL, M, SS, ES, and Finishline chassis. May be moved on the frame to adjust arm length and rate.

As far as manufacturing I'm with Schlaker.  I'm guessing they heat it up, bend it, heat it all the way up to annealing temperature and then let it cool in a controlled environment.

For the width the drawings measure 690mm (27.2in) between the outside of the mounting points.

Looks like the adjustable bars use a simple clamp for the end link that you can slide up and down the lever arm of the bar.  That makes a lot of sense.  Although I could still be looking at it wrong.

With the width of the stock bar (32in before it bends around the wheels) those all seem to wide.  Even the splined version.  For several reasons I think it is best to keep the bar as narrow as possible anyway; clearance, weight, and spring rate are all advantages of a shorter bar.  The narrower/shorter the bar the higher the spring rate will be at the wheel, which is nice because that encourages us to make the decision for more clearance and less weight.

thats only assuming the lca endlink location is constant.
you move that point further outboards on the control arm, your motion ratios change and wheelrate gets higher.
but as usual, clearance is the major issue on our trucks.

Yep that will change it too.  Just looking at the numbers using as rigid of arms as can be had and mounting to the suspension as far out as possible a narrow bar is the choice.  That is if you get to design your own.

Someone had said the more vertical to the LCA the end links are, the more consistent and efficient the bar will work. I lengthened my end links, got them straight at ride height, and i actually noticed a difference. They were too short since the energy links and bushings and there was a lot of bind. Now, my front end stays down thru the center and into acceleration coming out. (with the help of my shocks)

I'm going to rebuild the rear shocks to slow down the rebound on accel because i had a little too much weight on the front which made the rear want to become the front.

I think I'm going to do the change to 2wd like Daveman, because I'm running fantastic coil overs shocks but, with no room for the coils up front, I'm still using torsion bars for springs.

I might wind up scrapping the ZR2 all together, because i just bought an 86 Monte SS that I've been working on for my buddy for a couple years. I'm deeply conflicted by this.

Any pics of the lower control arms at ride height?