Grab 98' swaybar + lower arms to fit 91 ?

[N1446]

Will the lower arms on the rear of a 98 gtwagon swap directly to the 91 ss ? -to install the rear swaybar from the 98 i need the lower arms with the brackets correct ?

- just need to know what to grab along with the swaybar -

[Legacy777]

Yes the lateral links should work. Not sure about the bar, someone else can chime in.

[N1446]

ok i know from the sticky section the bar is a 16mm on the 98 , and i m lowering the car a bit so i m taking out the 18mm to compensate for the lower stance , i m on the right track i believe > i m a novice on the physics of the sway vs ride height

[beatersubi]

A swaybar of a given size will work the same regardless of ride height. Lowering a car, and thusly the center of gravity, will make it roll less to begin with. The swaybar will continue to work the same once it does.

[jamal]

keep the 18mm bar.

Lowering a car, and thusly the center of gravity, will make it roll less to begin with. The swaybar will continue to work the same once it does.

It's actually the opposite. Lowering the car moves the roll center down, and farther away from the center of gravity. That gives the car more leverage over the roll resistance, which creates MORE body roll.

[N1446]

ok if i understand correctly , lowering the hight of the ride lowers the center of gravity + the suspension is to get "tighter" with the use of a shorter / sportier lowering spring - in turn , shouldn t the stiffness of the spring w/c the lower center of gravity / ride height / ability to tilt , lessen the amount>?<of sway between the L&R posts ?[/i]

[skid542]

One thing to understand on Subaru's, we tend have a fairly high roll center compared to other vehicles. *my understanding at least

So while most people tend to lower the car and at the same time put stiffer springs on the car, it does roll less but that's really a result of the stiffer springs and not the actual lowering. Lowering your car, and all other things being equal, it will roll more.

And I don't mean to sound like a turd about this by anymeans - but Jamal knows his stuff on this one . Hopefully though he'll provide a little more indepth overview of why this is the case (though I think he may have covered this in a sticky somewhere... maybe?)

[beatersubi]

keep the 18mm bar.

Lowering a car, and thusly the center of gravity, will make it roll less to begin with. The swaybar will continue to work the same once it does.

It's actually the opposite. Lowering the car moves the roll center down, and farther away from the center of gravity. That gives the car more leverage over the roll resistance, which creates MORE body roll.

The best mod for decreasing roll and weight transfer, then, is stock height springs w/ higher spring rates and larger dia swaybars?

[jamal]

That, and a roll center adjustment kit like the whiteline one.

The suspension has what's called a roll center. Depending on ride height and roll angle, this roll center will move around. There is a roll center for the front and rear, and if you draw a line through them you get the roll axis of the car.

The roll center and roll axis are important because they are the point that the car tries to roll about. The lateral force generated by corning will act through the center of gravity around the roll center, creating a roll couple. Move the center of gravity and roll center farther apart, and you have more leverage to create body roll.

Lowering the car does lower the center of gravity, but it lowers the roll center proportionally lower. That means, that given the same roll resistance, a lower car will have more body roll. Sucks, doesn't it? That's why people put such massive swaybars on subarus for track and auto-x, despite the drawbacks.

[N1446]

ok .. in regards to the roll center , I have one more question

- if i add a brace between the top posts of the suspension plus lower the resistance on the bar from 18 > 16mm and lower the car while increasing the spring rate ; will this box-in the positive roll center ? I m aiming at a forgiving setup , one that gives in for the turn , yet holds at the same angle through it > i suspect with the 18mm bar the car is not about to flex very much - too stiff - and want to skidd out eventually and effect the "flikability" concidering the weight of the car -

i m convinced too stiff will be tooo badd

[skid542]

I'm not quite sure what you mean about boxing-in the positive roll center?

However, putting in a front strut tower brace is always a good idea. Putting in a lower control arm brace is also always a good idea (performance wise).

I really don't think you should be giving up your 18mm sway bar. 18mm is stiff, but it's not that stiff. There are a lot of people running larger bars.

And while you are right, too stiff often is bad if not done properly. It's usually worse if it's a daily/street driven car. However, until you get up into the 300-400+ lb range in spring rates you're going to be fine.

For reference, I'm running 245lb springs on all four corners on STi struts (this lowered me around .5" or so, not much). Stock front sway bar, adjustable rear (have it around 19mm), and stiffer endlinks. I also have a front and rear strut bar. Additionally I am running the Whiteline RCA kit. The car is stiff, handles well, takes bumps okay (you can feel them though) and is comfortable enough to be my daily driver.

What type of driving are you trying to set the car up for? I'm assuming since you're wanting to lower it, this is not for rally but instead street/tarmac?

[N1446]

i m saying box-in meaning bracing the suspension at the top posts with the struts/springs on either side and the sway bar connecting the bottom end together ; creating more of a trapezoid shape - containing the roll center from shifting with the distribution of weight
-
i am setting for tarmac / street performance ; fast transition through the S without loosing it super early in the turn w/c 18" 35series rim/tire
-
looking for moderate-low roll at 3-4" height

[jamal]

the roll center is just an imaginary point, of which the location is determined by projections through the strut towers and control arms. You can't prevent the suspension from moving so you can't prevent the roll centers from moving. But, there are things that can be done to reduce how far the roll centers move.

Here's a paper that is as far as I know modeled off of subaru front suspension, and shows the effects of lowering the car and adjusting camber plates:

http://zzyzxmotorsports.com/library/str ... 070918.pdf

more roll stiffness, camber plates, and a roll center kit are the best way to raise the roll center and reduce motion.

18mm isn't even close to being a stiff bar. I'm on 22mm front and rear adjustable bars, along with sti struts and springs, which are 225lb/in front and 195r. It's a pretty good combo for my performance all-season tires, but for on-road usage and sticky tires it could be stiffer (even though I do have less weight and more roll stiffness than a stock sti). I intend to pick up some racecomp engineering black springs and a roll center kit to further reduce roll.

[beatersubi]

The info in that link is very informative, thanks.

[N1446]

yess thankyou for that

[jamal]

One thing to keep in mind is that the paper only discusses the roll center, and not the other things that happen when you move the front strut tops. It's my understanding (and Robi's) that by increasing the SAI you decrease the dynamic caster gain. Unfortunately that's a whole other paper that needs to be done by someone with that software. Maybe I should call up zyzzx.

Anyway, the simple answer is that more negative camber and more roll stiffness will pretty much always be beneficial. This is also a reason why crappy shocks/coilovers are so popular.