Swaybar rates and how to figure (from old site)

[chicane67]

Author Comment
68LS1
Registered User
Posts: 148
(8/12/04 11:56 am)
Reply Sway bar rates....how do you figure it?
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What is the proper way to figure out the required sway bar rate? Is this a mathmatical deal or simply knowledge. I am running 500lbs springs in Alston adjustable coil overs up front. The LS1 and T56 weight around 700lbs. The subframe is from Scotts, not the factory piece. What should the rate be? Obviously the sway bar arm length (I'm talking about a swaybar like those by Speeedway Engineering) has a serious effect on the sway bar rate, but the sway bar size also affects the rate. Is the arm length determined more so by packaging needs or the spring rate you are looking for.

Hopefully that makes a little sense.

Thanks guys, Noel.
You can't stop here, this is bat country!

chicane67
Registered User
Posts: 215
(8/12/04 9:18 pm)
Reply | Edit Re: Sway bar rates....how do you figure it?
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R = (pi)(G)(d^4) / 50 (b^2)(L)

R = rate in pounds per inch
pi = 3.14
G = modulus of material (roughly 11,500,000)
d = diameter of bar
50 = constant
b = length of bar arm measured from center to center
L = length


If you give us some more information, I could probably get you in the ball park.

68LS1
Registered User
Posts: 149
(8/12/04 10:09 pm)
Reply What do you need?
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Holy cr@p. Ok Chicane, what other kind of info do I need to supply? I would certainly appreciate the help.

Thanks, Noel
You can't stop here, this is bat country!

chicane67
Registered User
Posts: 220
(8/12/04 11:02 pm)
Reply | Edit Re: What do you need?
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As your attorney, I advise you to rent a very fast car with no top.........

I would also like to know the shock valving rates for your shocks. Next I will need your rear spring rate and then I will need to know any other modification you have done to your chassis.....specifically any weight that you may have mooved around.....battery in the trunk, addition of roll bar...etc.

BTW, I think you a little too optimistic about the weight of your Ls1 and T-56 combination.......

But fill me in.

68LS1
Registered User
Posts: 150
(8/13/04 12:13 am)
Reply Re: What do you need?
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AAAhhhhh I see we have another Fear and Loathing fan.

....we'll need some Acapulco shirts, a tape recorder for special tapes, and of course, we'll need the cocaine....and we must arm ourselves, to the teeth. hahahahahahaha

Anyway, I will have to do some investigating when I get home. I'm offshore right now and will be for another 2 weeks. I really appreciate you input Chicane. How optimistic do you think I'm being on the weight of the LS1/T56?

Chill, Noel.
You can't stop here, this is bat country!

[Ralph LoGrasso]

Is it really worth going with a custom bar? The only thing stock on Fantom will be the sheetmetal really. I'm starting to wonder if I should do a custom bar, or just use the 1" Herb adams solid bar that I already have? Chicane?

[68ls1]

Speaking for myself, the price of the custom piece from Speeway Engineering is very reasonable and it gives me the ability get the rate I need, not the rate an aftermarket bar comes with. It will be easier for me to package as well.

[chicane67]

Ralph~ You may as well start with what you already have.......and tune from there. There is no reason to spend more money on another one, until you have put the first part through the ringer to see how it works.

Noel~ Great points. It is eaiser to change the rate of a bar designed to the likes of the Speedway bar. And yes, at times it is eaiser to package, not to mention that it is a cost effective way to have an adjustable bar....

[72SSAbody]

**Devil's Advocate**

The "G" value is a material property. Just to give everyone a heads up...materials used are generally proprietary info of the company making **cough cough**...ehhh...marketing!!...the product.

Thus keep in mind this will only get you in the ball park for spring rate.

**Devil's Advocate**

[airrj1]

Who let the Engineer in? :moon:

[chicane67]

Generally proprietary........

Generally, yes. However, metalurgy in specific to stay bars is considered in the "rough" figure for modulus. Solid type bars are so close in ~Rockwell~ the acceptable measure of uncertainty is scrubbed.....and honestly, they are not different enough in material to make any noted difference. Now "heat treat" on the other hand.......

Now as for hollow stay bars, that is a totally different animal. They have to be estimated/rated somewhat differently. Not to mention, that lever arm ratio and length have a greater influence on the actual tortional loading of the bar or center tube itself, depending on its design.

Mount location and ridigity have to kinda be thrown in here for thought as well. If you install a larger bar than what was run factory, you run the risk of ripping the 'mount surface' right out of the frame. This is actually a common occurance when someone installs too large of a stay bar and/or not enough front spring rate.

It is also more common on the rear suspension that utilizes a mount that is bolted to the frame rail and has the long/extended links to the bar itself. Considering that the rear suspension does not require a rear stay bar, you might be getting the picture of what can happen when you install something that isnt needed or required in the first place and that was designed as a bandaid fix from the get-go.

Spring....to vehicle load requirements

Shock....to compliment and dampen the spring effectively

and Stay bar to tune.

[David Pozzi]

Here is a handy bar rate calculator: http://www.stockcarproducts.com/pstech6.htm

I haven't tested it to see if it varies from the forumla results.
When you get a stiff bars the mounts make a large difference in actual rate transmitted to the tires.
David

[72SSAbody]

Now "heat treat" on the other hand.......



Sorry, I should have stated in my original post that material properties ment "after all processes have been completed in the product"....

Speaking of heat treatments. I've seen a couple of GM rear sway bars snap from an inproper heat treatment. The material would go into the plastic region and work harden itself to death.

:seizure: <~~How the drivers look when they tell me what it sounded like in the car.



Now as for hollow stay bars, that is a totally different animal. They have to be estimated/rated somewhat differently.


This should be pretty easy (that is, if I can remember from my materials design classes after a day of listening to V-Twins rumble in my ear all day). One of the most important aspects of calculating spring rate is your polar moment of inertia. When you do this calculation you're pretty much finding out the inertia of the bar plus factors from the material properties.

For a hollow bar you'll need to take (O.D.^4-I.D.^4) and then go on to plug the rest back into the equation.

You guys are actually making me want to break out the materials design book and check up on myself :comp3:

RJ,
Yep, I try to get away from engineering, but even after I do this: :help!: it keeps coming back.

Joe

[David Pozzi]

You can use the calculator I posted above, use the ID of your hollow bar as the OD entry in the calculator. Then calculate a hollow bar using it's actual OD, subtract the first bar rate from the second to get hollow bar rate.

It's not as elegant but it will work.
David

[BB69]

I have an Excel sheet at home that calculates hollow or solid bars given pretty much any geometry. Most cars don't have straight bars, and the bends affect the stiffness. I can email it if anyone wants it.

Ken