antilag_200

iTrader: (49)

Quite the arguement happened on one of my local forums regarding increasing the length of an endlink, to basically preload your front sway bar... I did some good old fashioned mathematical analysis of the member and came up with the following concept

So here is the install
Here is the stock end link vs the whiteline piece.

it was a good thing that I took care of this, as the stockers were completely messed up.

after some rough measurements of the stock links, I figured that I would add an additional 10mm to the whiteline endlinks. This "should" preload the swaybar a little bit more than what comes in the car from the factory.

Here is the finished product, nice and easy.

and a good shot , showing the whiteline tierod ends


Now for the theory
by loading the bar statically , you are increasing the torsional force of the bar in relation to the control arms. Kind of like bending a tube, The more you bend it, the harder it is to deflect, until you go past the yield point. So in my mind, yes you are effectively making a bar of a given diameter have a higher rigidity just by increasing the length of the endlink, which would be the same as just increasing the diameter of the sway bar. Makes sense ?

Here is a quick moment and shear diagram which would make it a little easier to see how I envision a sway bar working with extended links


If my moment and shear diagrams are correct, then by increasing the length of the endlink, you increase the cantilever at the edge, which in turn, increases the moment, which "should effectively increase the rigidity.

Still with me folks , last but not least the static equilibrium forces illustrated


page two


Please feel free to disprove what I have illustrated above. I am just trying to get other peoples thoughts and math behind a rather simple concept. Maybe its not that simple

rawkus

iTrader: (16)

I have no clue about any of the math above... and I really don't like learning, but I have a few thoughts...

What do you mean by "preload" the sway bar?

You state that you added approx 10mm length to the end links to increase preload, but if you add an equal amount of length to each end link, you do not add any preload.

A sway bar is a torsion spring that connects the driver's and passenger side suspension. You CAN increase preload by binding the sway bar, increasing the length of one end link while decreasing the length of the other. But increasing or decreasing end links the same amount side to side does not increase preload.

The reason being is that the sway bar rotates. Looking at your diagram is appears you think that a sway bar mounts solidly to the crossmember (which is does to some extent), but the sway bar can rotate within its bushings.

I guess in theory you could increase preload by pointing the sway bar straight up when the suspension is normally loaded, this would mean that when the suspension is compressed by a bump or loaded by a turn, the end links would bind and not allow the bar to rotate, but I would think you would have all sorts of other issues and it is easier to increase spring (wheel) rate by get stiffer springs.

Maybe you are talking about something else... in which case, ignore my previous statements!

Dan

antilag_200

iTrader: (49)

Thank you for your thoughts, what I provided is a simple analysis statically (dynamic behaviour is in no way being analysed currently), So when I say preload the swaybar, I have illustrated it in the diagrams by the vertical force only in relation to changin the vertical length of the endlink.

Now in response to your sway bar rotating in a bushing... it will do that in an extreme case for sure , or your bushings are really worn out.

rawkus

iTrader: (16)

I reread this and you are right as long as by preloading the bar you mean, increasing the length of one end link in comparison to the other end link. One problem is having bind on the bar when the car is static which can create more wear and tear on the end links. I am sure there can be other issues, maybe someone else can chime in with more experience.
Dan

KevinD

iTrader: (56)

^what he said. if you lengthen both sides, you didn't do anything because it rotates inside the mounts.

if you lengthen one side, and shorten the other (i guess you could call this preload), you in effect will be enducing a roll on the rear suspension statically. you will have uneven suspension characteristics if you did that.

when corner balancing a car, your sopposed to disconnect the sway car all together, get ride heighs correct, then reconnect the bar such that there is no "load" on the bar.

the easier way to make the bar stiffer is to use a thicker bar, or shorten the sway bar arm length where the endlink connects.

rawkus

iTrader: (16)

Sway bars are designed to rotate within your bushings. Think about it, they are only meant to increase spring rate when one side of the suspension is compressing and not the other. If you hit a speed bump on both front wheels at exactly the same time then sway bars have zero (or damned near zero) effect on the spring rate of each individual wheel. But if you hit a bump with only one wheel, the sway bar will increase the spring rate on that wheel because it is connected to the other suspension and will try and compress it.

If a sway bar wasn't meant to rotate, it would be useless, you would just increase spring rate by changing the main spring on that corner of the suspension.

Dan

rawkus

iTrader: (16)

Thanks for the help Kevin, but one question for you. How would you have uneven suspension characteristics? The sway bar has an equal, but opposite reaction on both ends, just because there is bind in the bar it wouldn't load or unload one side more then another... am I wrong?

Dan

antilag_200

iTrader: (49)

Ok that does make sense that the bar rotates, now if we look at just the bushing that the sway bar is in , that would be exerting a vertical and horizontal ( in the plane of the car) force, which is what would reduce the roll. Effectively acting like a larger sway bar. ( I am trying to look at this from a summation of forces in the X, Y direction)

KevinD

iTrader: (56)

the bar is a spring when twisted. when you have an equal but opposite reaction one side to the other, one side will have more K, the other less K. remember the total K is the bar K plus the main coilover K. since obviously we want balance, you want the combined K of the sway bar and the spring on each side to be equal. the only way to do that is to have no preload in the bar.


for example, you are pulling Gees, car starts to roll, when it rolls, it begins twisting the bar. the twist of the bar from the outside wheel increases its K(which statically would be the same thing as increasing the length of the end link)and it decreases the K value of the inside wheel effectively is compressing it.

and since this one is a hard one to visualize, i may have my K values backwards

Dallas J

iTrader: (1)

The only way to pre-load a sway bar is to essentially pre-twist it in one direction which is what you would be doing if you adjusted one end link and not the other. This would give you more roll resistance in one direction and less in the other.

In the end though, if you dont have your car corner balanced then worrying about sway pre-load is sort of a moot point. In fact if the corner weights are off you may even have slight improved performance from a preload.

As far as being able to preload the bar to act like a larger bar in both directions, no. Gotta make a physical change for that.

hotrod2448

We do this in oval racing. You are pre-loading it in one direction. It is not the same as increasing bar diameter and keeping the bar neutral. What about when you have to turn the other direction?

KevinD

iTrader: (56)

when you have to turn the other direction the car rolls twice as much

hotrod2448

That's why we just go left.

4bangn

so for the average driver, in plain english please, what is the point of this

rawkus

iTrader: (16)

Thanks Kevin and Dallas! That clarified it for me instantly.

Dan