[kessler89]

on my wl FSB 27-29 which is 27? if the bar is on the car and you're looking at it from the front bumper, which setting is 27? front or rear hole?


thanks

[Turninconcepts.com]

rear hole

[sti robot]

The holes further out from the center of the bar itself make it less stiff. Think of it as a spring and it'll make sense.

[Turninconcepts.com]

Originally Posted by sti robot

The holes further out from the center of the bar itself make it less stiff. Think of it as a spring and it'll make sense.

the front bar can look a little confusing.

[allwheelsdriven]

yes closer to the bumper is stiffer

[sciolist]

Okay, here's a related question:

Obviously lengthening the moment arm from the bar's primary neutral axis to the attachment point results in a 'softer' bar. The relative stiffness of this bar is expressed in terms of nominal diameter (27mm vs 29mm). The idea is that changing the moment arm's length produces the equivalent stiffness of a bar with a different diameter.

In order for this to make any real sense, there would have to be a standardized moment arm length, though. The bar only has one nominal diameter. What if we compare another bar with the same diameter and a different lever arm? It's going to have a different stiffness.

It's easy enough to compare a hollow bar to a solid bar with conventional section modulus formulas, but what's the convention for the lever arm length?

There's no problem having adjustable bars with different diameters, but when you start equilabrating them in terms of diameter, there has to be a convention for the moment arm.

[Turninconcepts.com]

Originally Posted by sciolist

Okay, here's a related question:

Obviously lengthening the moment arm from the bar's primary neutral axis to the attachment point results in a 'softer' bar. The relative stiffness of this bar is expressed in terms of nominal diameter (27mm vs 29mm). The idea is that changing the moment arm's length produces the equivalent stiffness of a bar with a different diameter.

In order for this to make any real sense, there would have to be a standardized moment arm length, though. The bar only has one nominal diameter. What if we compare another bar with the same diameter and a different lever arm? It's going to have a different stiffness.

It's easy enough to compare a hollow bar to a solid bar with conventional section modulus formulas, but what's the convention for the lever arm length?

There's no problem having adjustable bars with different diameters, but when you start equilabrating them in terms of diameter, there has to be a convention for the moment arm.

And that starts to get into the problem of there being no real published "rates" for aftermarket sways, just effective diameters. It's been a sore spot for a long time.

I've had an idea for some time to make a test rig and test as many bars as I can get to give us all real world lb/in units, but have not had the time to work on it.

[sti robot]

Originally Posted by Turninconcepts.com

And that starts to get into the problem of there being no real published "rates" for aftermarket sways, just effective diameters. It's been a sore spot for a long time.

I've had an idea for some time to make a test rig and test as many bars as I can get to give us all real world lb/in units, but have not had the time to work on it.

Yup, I agree. To do a real comparison you would need spring rates for each sway at each position. Diameter is relative. There are other things that change the spring rate of the bars including how the metal mixture (alloy) used, how thick the walls are, hollow vs solid, etc.

[sciolist]

The other variable is material.

I agree that the easiest (and most conventional) approach would be to work in terms of rate, just like with any other spring.

To the extent that it says anything about rate, the diameter is really a nominal specification. Generally useful, but not very inclusive.

In the context of setting up a car, the bars' adjustability is more important than having an absolute quantified rate. In terms of procurement though, it would sure be nice to know the true rate of at least one of a given bar's settings.

[sciolist]

I don't think so. All you really need is a Modulus of Elasticity for the material, Section Modulus for the bar and the length of the moment arm.

It would be easier to just work in terms of rate delivered to the pick-up, though. For example, when I go from a #625 front spring to an #850 front spring, I'm not all that concerned about the precise metallurgical content or stock diameter in what Eibach sends me - really just the rate... and of course length and diameter for fit.

Originally Posted by sti robot

Yup, I agree. To do a real comparison you would need spring rates for each sway at each position. Diameter is relative. There are other things that change the spring rate of the bars including how the metal mixture (alloy) used, how thick the walls are, hollow vs solid, etc.

[Turninconcepts.com]

Don't forget how a bar is heat treated. That also affects stiffness.


See, and all of this would be much easier if we had a chart that said something like this:

Bar.........Postion1.....Position2.....Position3
X7-42R.....185...........212.............225
B47W9......155..........163.............172
ID-10T.......5.............92..............847

The test rig would be really easy to build, maybe a little costly since I want the base to be 1/2" steel plate. I've been thinking about the test itself as well. Here's what I'm thinking:

For each setting on the bar - be it fixed or adjustable
1 reading at 1" of load
1 reading at 2" of load
1 reading at 3" of load

Linear distance between each point to see if rate is linear with the bar.

[sciolist]

That's built into the Modulus of Elasticity number.

Originally Posted by Turninconcepts.com

Don't forget how a bar is heat treated. That also affects stiffness.

I agree that charting the data would be very helpful.

[kessler89]

sweet, thanks guys, i got the bar put on today, now i'm waiting on the rear, it should be here tomorrow cant wait, i figured a good starting point would be 27f/24r and then adjust from there

[Web_Foot_STi]

Sad thing is I understand all of this...

[NewShockerGuy]

Question.

How do you know which hole to put it in first (KEEP IT CLEAN...lol :-p)
As far as handling goes... If you have it at the highest setting for the front what happens as oposed to the least?

Reason I am asking is I am going to be getting some things installed soon and would like to know how the car would handle differently from STOCK form?

Thanks,
-Nigel