Sway Bar Rates

[Track Junky]

I'm in the process and planning to relocate my front sway bar to the top of my frame rails. In order to do that I need to know what my existing sway bar rates are so that when I go to a splined bar I know what size bar and length of arm to go with. Also going to drill 3 holes in the arms at 1" apart for adjustability.
I called Hellwig, DSE, Hotchkis, and Global West and this is what they gave me.

Hellwig 1 1/8 Tubular 600 lbs/in
Hellwig 1 1/8 Solid 720 lbs/in
DSE 1 1/8 Tubular 1532 lbs/in
Global West 1 1/8 solid 1279 lbs/in
Hotchkis 1 1/8 Tubular 750 lbs/in

[Flash68]

Does that make sense that Hotchkis' tubular has a higher rating than Hellwig's solid in the same diameter?

[Motorcitydak]

75% of the torsional (twisting) load is handled by the outer 25% of the material in a bar...but still usually a hollow bar has to be slightly larger in OD to equal a slightly smaller solid bar. Perhaps it has to do with the chemistry of the metal?

[Track Junky]

I was blown away at the numbers they gave me. I was expecting to see around the 450 lbs/in range.
If you go to Speedway Engineering's website the 1 1/4" x 42" solid bar is 498 lbs/in with a 10" arm.
I realize that the bars I listed only have about a 6 1/2" arm but regardless of that the rates I was quoted seems huge.

[Track Junky]

Now it should be stated here what sway bars essentially do, even though I know you may already know this. What a sway bar does is counteract the action of body roll during cornering by transferring spring rate from the inside wheel to the outside wheel in a corner. This means that you don't actually get any added spring rate; you just subtract it from one side and add it to the other. This has the ultimate effect of transferring load from the inside tire to the outside, which has the visual effect of compressing the suspension on the inside of the turn and expanding the suspension on the outside of the turn (thus limiting body roll). This is good mainly because it smoothes the speed of weight transfer during quick transitions and also limits the camber change experienced at the corners of the car through suspension travel. And of course, using this concept one can dial in the amount of total loading on the outside tire by varying the effectiveness of the sway bar (stiffer bars equal more transfer). And the beauty of all this is that it mostly only occurs during cornering, so our straight line spring rates are not affected. The other thing Ok, so hopefully now you all understand this concept. This is the most important part though, so if anything is still fuzzy read this again until you get it. Also, here's an example of how this works:

-For this example we will use a sway bar with a roll stiffness of 250 lbs.
Left front static load: 1000lbs
Right front static load: 1000lbs

-lateral weight transfer in a right hand turn
Left front: + 500lbs
Right front: - 500lbs
Total weight transfer: 1000lbs

-load transfer of sway bar(which is 250 lbs):
Left front: +250lbs
Right front: -250lbs
Total weight transfer: 1000lbs

-total effective cornering load for this example:
Left front: 1000 + 750= 1750lbs
Right front: 1000 - 750= 250lbs

-without sway bar
Left front: 1000 + 500= 1500lbs
Right front: 1000 - 500= 500lbs

[Track Junky]

Does that make sense that Hotchkis' tubular has a higher rating than Hellwig's solid in the same diameter?

None of those numbers make sense to me. Look at the hollow DSE as opposed to the Global West solid.

[Track Junky]

75% of the torsional (twisting) load is handled by the outer 25% of the material in a bar...but still usually a hollow bar has to be slightly larger in OD to equal a slightly smaller solid bar. Perhaps it has to do with the chemistry of the metal?

Could be, but those numbers I was quoted seem high. According to Speedway Engineering, they test the bars by twisting the bars 5* which he told me equated to 1" of bar lift.

Doug at Global West was the last of the manufacturers that I talked to and he told me he tested the same way.

Another thing about the bars I listed is that the manufacturers dont tell us wall thicknesses for the hollow bars.

[Sieg]

This software may be worth the money:

http://www.speed-wiz.com/

http://www.speed-wiz.com/calculations/suspension/anti-roll-bar-calculation.htm

I have no first-hand experience

[Track Junky]

Thanks Sieg, neat software and inexpensive.
In order for me to achieve the rate of my currently installed DSE sway bar with a relocated splined bar with 10" arms I would be to go to a 37 1/2" long bar.
Something doesn't seem to jive. Dont see how the rates could have such a large spread.

[Vegas69]

Are some manufacturers using combined and others individual values.(Both sides vs. one)?

[Track Junky]

Thats what I was thinking. When I talked to Speedway Engineering they told me that they twist one side 5*. Global West told me they did it the same way. I'm going to have to get more information on Monday.

[David Pozzi]

They are using different methods of calculating rate.
Here is a free online calculator: http://www.auto-ware.com/calcs/swaybar.htm
The Hotchkis hollow bar is .156" wall, Hellwig hollow is .188" OD is 1.125 but the powder coat can add .020" which you don't want to count.

I recall Speedway rates with a flat 5deg twist which will be 1" with an arm length of 11 3/16" only, the other arm lengths listed are useless numbers. 1st gen Camaros have a very short arm. Some calculators use 1" arm movement on each arm, so your calculated rate is double. It's best to take the dimensions and re-calculate them using one formula or online calculator. The bent hollow bars are not Chrome Molly steel, the Hellwig solid is and so is the Speedway hollow. I think the Modulus of elasticity is different between the two but most online calculators have the modulus Pre-entered so you can't change it.

[Track Junky]

Dave, Standard OEM bar shape tough to figure how to measure. When I measure length of bar on the Global West and DSE bar do I measure from outside to outside of straight or take it to the outside of the 22.5* bends.

[David Pozzi]

I use the inside of bend to inside of bend. I don't think of bar rate as an accurate number, just as a way to compare one bar to another. There are too many unknowns, like bar mount flex, end link flex, frame flex. Then the bar has a motion ratio that translates to wheel rate, so the bar rate at the wheel is maybe half.
changing from splined bar to splined bar is easier to compare. The Global West and DSE numbers might be inch pounds per degree or per 5 degrees, hard to say.

I can tell you I have used the Hotchkis hollow and it's about right, the Hellwig is one step stiffer but it will take more rear bar to get the car balanced assuming a front tire if 275 & rear if 335. If tires are more equal the Hellwig works OK.

Try using this HTML sway bar calculator. The original web calculator is no longer active but I saved a copy of it and it works pretty well. Great for comparisons. I would reload the page when entering new bar dimensions, it sometimes can give wrong results if you jump in and change the numbers, but I'm on a Mac with Firefox, so maybe it's my computer.
Note keep the slider for motion ratio to the right at 1 to 1 unless you know your sway bar motion ratio. http://www.mediafire.com/?jteoqxvspc4ozq0
This is a free download hosting site, so it will have popups, sorry.

[Track Junky]

Thanks Dave. I agree the numbers are ball park but none of those numbers make sense to me.

I have a Global West bar and a DSE bar. I did feel like I got a touch loose going to the hollow DSE bar but still not sure what to make of it.
If I were to take Global Wests and DSE's numbers seriously I'd have to say going to a bar with more lbs/in up front made me lose which means I got more grip up front with more weight transfer.

[Dave@Hellwig]

Track Junky. I think we talked last week about rates. We use SAE formulas to calculate the spring rates we give out. The rate I gave you includes a 20% reduction to account for compliance in bushings, end links and frame mounts. This factor has correlated fairly well between real world testing and calculated rates. The rate of our 1-1/8" tubular bar without any loss is 750 lb/in.

[Track Junky]

Thanks Dave@hellwig. I do remember us discussing the compensation for reduction. Your input was very informative and I appreciate your help. :thumbsup: