flyingscot

iTrader: (2)

does anyone happen to know the stock swaybar rate in pounds(lllbs)
i think they are 25mm front and 23mm rear but i need the poundage at 5 degrees of twist if anyone has that info,thanks in advance

killerpenguin21

iTrader: (20)

im also very interested in this info, as well as if anyone may have calculated for any of the popular aftermarket bars.

BEKevo

iTrader: (2)

Wouldn't that be torsional rate? I searched for quite a bit and could not find any info..

Im interested in knowing this as well.

BEKevo

iTrader: (2)

What is the OEM sway bar made out of ? 4130 chromoly?

killerpenguin21

iTrader: (20)

most papers ive read assume bars are just mild steel. there is a formula:

500,000 D^4
K (lbs/in) = -------------------------------------
(0.4244 x A^2 x B) + (0.2264 x C^3)


B
-----_________________
A| /----------------------------\ C
| /------------------------------\

A - Length of end perpendicular to B (torque arm - inches)
B - Length of center section (inches)
C - Length of end (inches)
D - Diameter bar (inches)

then use:

WHEEL RATE = K * Mr ^ 2

but there are many factors you have to take into account like the mounting point flex etc. but i do think you could at least get a ball park figure to help you combine a bar/springs to get pretty close to what was desired.

realistically there is a whole bunch of other stuff that needs to be figured too like roll center and spring frequency...its a giant can of worms.

flyingscot

iTrader: (2)

im not sure what any of that means,math was never a strong point,what would be a ball park range for lets say a 25mm rear bar?im thinking the stock bar would be around 500 llbs

alleggerita

An identical 25mm bar is 18% stiffer than a 24mm bar...

killerpenguin21

iTrader: (20)

the stiffness calculations are separate from all this.

BEKevo

iTrader: (2)

ahhh.. I remember this formula... You can figure out the swaybar rate in ftlbs, while not being mounted. But this information would be fruitless, as killerP pointed out. There are so many variables that affect the "swaybars" rate (ie mounting points, spring rates/frequencies etc.. )

Iowa999

iTrader: (1)

A lot of other values are needed for this (and I'm in the process of collecting said values for Evo Xs right now, as [bad] luck would have it).

Besides the 4 basic measures of the swaybar, itself (i.e., the A, B, C, & D from the Fred Puhn formula), you need the motion ratio of the bar as it attached to the car. Then you'll be able to calculate pounds/degree.

Out of curiosity, why do you want pounds for 5* of roll? The more typical ways to describe the effects of bars is to either add their effect to that of the main springs to compute the total wheel rate in single-wheel bump and/or to compute the amount of body roll for a particular lateral g. The latter, of course, requires even more missing information, such as cg height, track, etc, but is one of the ways that people talk to each other, as in, for example: 3.5* of roll at one g.

Iowa999

iTrader: (1)

Besides A, B, C, & D from the Fred Puhn formula, you only need to know the swaybar's motion ratio to calculate the effect on single-wheel bump. This all assumes infinitely stiff bushings, which is, of course, nonsense, but there aren't as many other variables as you seem to be suggesting.

Again, assuming infinitely stiff bushings and no play in the end-links, once you have the effective K for the bar from Puhn's formula, you multiply by the square of the motion ratio and add this to the wheel-rate K from the main springs.

BEKevo

iTrader: (2)

Interesting note on Puhn's formula ^ thanks for the correction

---Side note: IOWA999 i love the 15" braids!! looks great on the X. Looking for a set myself.

Iowa999

iTrader: (1)

You're welcome. Swaybar math is both simple and complicated. The simple way to look at swaybars is that they are twice as effective against body roll as they are against single-wheel bump. So, if you want to stop the car from rolling so much but want to keep the suspension somewhat compliant, you use a lot of bar relative to the amount of spring. The complicated way to look at swaybars is to actually calculate the final wheel-rate for single-wheel bump when both the bars and main springs are included, as well as calculate the amount of roll for a given lateral g (or the amount of weight transfer required to roll the car one degree, if you prefer).

The reason why I have been so interested in the complicated approach is two-fold. First, I've been trying to figure out if it would be possible to create what might be called a multi-purpose duffer-mobile: rallycross with the swaybars detached and autocross with the swaybars connected. I'm worried that this will end up such a compromise that the car will stink at both, but I really want to try it for Ss & Gs.

Second, I cannot for the life of me figure out why no formula for desired initial damping ever includes the effect of the swaybars on single-wheel bump. The reason for wanting to know this relates to the above duffer-mobile. If I get shocks that are correct for, say, 4K springs on a rough surface, how badly will said shocks be when large swaybars are added for tarmac?

Dallas J

iTrader: (1)

Material is irrelevant because most steels are all just about the same modulus of elasticity, though if you want numbers look up spring steel. It most likely what youll find the bars made from.

Absolute numbers are nearly useless (to 99.99%) of people. You are better off looking at change in stiffness. Roughly speaking, you can get it by:

Diameter change: 1 - Dold^4/Dnew^4. (Larger Diameter is stiffer, results in positive number)

Leg length change (If my math is correct): 1 - Anew^2/Aold^2. (Longer leg, softer bar) (This also assumes B is more than several times the length of A & C, and the results will be off a couple percent of the overall change depending on several bar specific factors).

Iowa999

iTrader: (1)

I totally agree that you can use the 500,000 constant for pretty much any material. I also agree that diameter (D in Puhn's formula) is raised to the fourth power. And I also agree that Puhn's formula is for standard-type swaybars made from one piece of bent bar with a body length (B to Puhn) that is very high relative to the other lengths. However...

Lever-arm length (A to Puhn) is the one that is squared. Leg length (C to Puhn) is actually cubed.

edit: I just noticed that you wrote "Anew" and "Aold," so we are not disagreeing about what power to use for A. It's merely a labeling disagreement. The correct name for A is "lever-arm length" or "effective lever-arm length"; the term "leg length" is used for C.