sway bar sizing

[simonasaur]

Ive got a 91leg that i want to get a sway bar for. I was wondering what size you guys run, is there signifigant difference in just 1 or 2mm, is whiteline the only supplier for our cars, does the bar make that big of a difference, would a front sway bar promote the car to dig in corners like a rear promotes the tail to step out????

Lots of questions, any knowledge would be appreciated, thanks.

[Legacy777]

I would say whiteline is the main supplier of aftermarket sway bars for our cars. There may be others, but I'm not real sure of them.

The size of bar is really dependent on your current suspension setup, and also how you want your handling to be like.

On a stock suspension car, bumping up 2mm or so would probably give you more neutral handling and less body roll. In my original setup, I went from the stock 16mm bar in the rear to a turbo legacy 18mm bar. That improved body roll and handling. When I installed my whiteline springs I noticed there was more understeer and the car wasn't as neutral. I upgraded to a 20-24mm whiteline bar. I'm running it in the 20mm spot right now, and I'm very happy with the handling.

[scottzg]

A larger rear sway bar will increase lateral road holding and allow more lift off oversteer. A switch from a 18 to a 20 is a 52% increase. Something worth considering is that the swaybar is essentially a big spring, so it may not be prudent to put a giant bar on worn struts or gr2's that are already being worked by even stiffer aftermarket springs. Add this to the fact that many of us are running more front biased impreza suspension (sheepishly raises hand) and those poor struts might be a bit overworked. Flame away.

[simonasaur]

Thanks for the replies guys.
I dont know what flame away means, sounds like a homosexual referance to me

Ive been asking around and so far every one says i should get a white line adjustable bar. Sean over at rallitek was explaining what "adjustable" means and he also explained how it was esentally a spring.

Im running hks springs with wrx stock struts and a rear upper strut brace. Im super happy with my set up right now, but i just got some 18" today so anything to decreace the rubbing will be awesome. Oversteer is a good thing!!!!!!

[BAC5.2]

A sway bar won't decrease the rubbing... The right wheel/tire and suspension will decrease rubbing.

[simonasaur]

Thanks for that enlightening post

[JasonGrahn]

Thanks for that enlightening post

Don't mock. He's very correct in most aspects. True, a larger rear sway bar will lessen the tendency for the rear of the car to squat to one side or the other while corner, but unfortunately, most rubbing occurs on the front wheels. Ride height adjustment and the correct wheel/tire combination solves this to a large effect.

And if course, it's posts like yours just above that make board members not like other board members. A somewhat better response could have been "Please enlighten, as I do not agree wholeheartedly."

[JasonGrahn]

A switch from a 18 to a 20 is a 52% increase.

Thats a good link scott, but it doesn't look like it takes into account wire types used for manufacture nor design; whether the bar be hollow or not.

[BAC5.2]

I read somewhere that hollow bars are akin to a 1mm smaller solid bar. I.E. a 19mm hollow bar is about as stiff as an 18mm solid bar, but it's a lot lighter.

My neighbor has a 26mm rear bar on his Taurus. That thing is monster. He's got a 24mm going in up front. He lifts a tire when he pulls into his driveway, pretty funny actually.

Jason - What do you think sway bars do for straight line traction? I know super stiff bars are bad for snow traction, probably due to the ability of each wheel to move independently of eachother.

Simonasaur - Don't like my input, don't listen to it. If you rub in the rear under compression, you will still do so. A head on hit at a speed bump, a swaybar isn't going to decrease the suspension travel much at all. While you MAY rub less in the turns (and I stress MAY, as sway bars do their best work on smooth surfaces, a turn on a bumpy road where the outside hits a bump, the inside lifts for a split second with the stiffer bar), in straight on hits, the sway bar isn't going to do a whole lot.

Also, like Scott said, a big bar can overwork the struts. So coupled with rubbing, you now have a hella bouncy ride.

SO, like I said. If you want to decrease rubbing, you should first worry about your wheel/tire choice and your ride height. THEN worry about band-aiding minor rubbing with big sway bars.

What is your wheel/tire choice and specs?

[JasonGrahn]

Jason - What do you think sway bars do for straight line traction?

Front and rear sway bars or anti-roll bars are designed to reduce body-roll during turns. They have no influence on the suspension when wheels bounce in unison (straight lines). They only come into play when they are twisted, that is, when vertical movement on one side of the bar exceeds the vertical movement on the other side, as when the body rolls or only one wheel goes over a bump. In addition to reducing body-roll, sway bars also reduce the adhesion limits of the side-by-side wheels that are being acted upon. This allows sway bars to be used as suspension tuning devices. By varying the stiffness of the front and rear sway bars you can influence the oversteering or understeering characteristics of a car.

I know super stiff bars are bad for snow traction, probably due to the ability of each wheel to move independently of eachother.

You know this? how so?

Also, like Scott said, a big bar can overwork the struts. So coupled with rubbing, you now have a hella bouncy ride.

The heartier a suspension is built (ie; the less slop it has) the more it allows the struts and springs to do what they are designed to do - therefore the suspension would work betta. Of course, this is only to a degree and depends on the suspension design.

[Legacy777]

I'll concur on the rubbing issue. I had to work with rubbing issues when I was looking for wheels. Back in the day you couldn't find any wheels with more then +40mm of offset. I had one guy say, just don't go fast around turns......it doesn't work that way.

Hollow anti-sway bars, actually are pretty cool. The reason they are almost as stiff and strong has to do with the hoop stress. The amount of stress/forces in the bar get larger towards the outside of the bar. Since the inside portion of the bar does not support/resist as much stress as the outer portion a hollow bar is only slightly weaker then the a solid one.

[scottzg]

My neighbor has a 26mm rear bar on his Taurus. That thing is monster. He's got a 24mm going in up front. He lifts a tire when he pulls into his driveway, pretty funny actually.

you can't compare a swaybar from one manufacturer (or even model, often) to the next because on a different car the lever arm of the bar could be a different length, altering the effective rate. Just like how adjustable bars work.

Im running hks springs with wrx stock struts and a rear upper strut brace. Im super happy with my set up right now, but i just got some 18" today so anything to decreace the rubbing will be awesome. Oversteer is a good thing!!!!!!

A non-sti subaru will never on-throttle oversteer in any practical application.
Uprated springs on 'stock' struts from a car that has a heavier front weight distribution(and less weight in the rear). Do you really want more spring in the back?


The wider front track on the wrx sedan is the reason the wrx rear bar is wider. What is true on the wrx rollbar-wise is not true on a legacy. The wrx wagon has the smaller bar because it doesnt have the wide front track.

[scottzg]

Also, like Scott said, a big bar can overwork the struts. So coupled with rubbing, you now have a hella bouncy ride.

I didn't say that! while the bar has a significant effect on cornering, a swaybar upgrade has a negligable effect on ride quality. They only affect the suspension in transition. Sure, drive over a human head at 25mph and it will be less pleasant (if that's possible) but the minor bumps from imperfect roads will feel exactly the same.

[BAC5.2]

Add this to the fact that many of us are running more front biased impreza suspension (sheepishly raises hand) and those poor struts might be a bit overworked.

hehe, you DID say that...

Overworked struts means they have insufficient damping. Insufficient damping = bouncy ride.

Hitting uneven bumps (pot-holes, for example), is where the decrease in ride quality comes from with sway bars.

I wasn't comparing the Taurus bars to Subaru bars, I was simply telling a tale about super stiff bars.

Jason - When the wheels hop in unison, it wouldn't do anything, but if you unload to one side (like open diffs tend to do), how will a sway bar handle 1 wheel trying to pogo away while the other... isn't pogo-ing away? That's more what I was getting at.

I meant to change the "know" to "heard". Proof read Phil. Proof read .

[scottzg]

Add this to the fact that many of us are running more front biased impreza suspension (sheepishly raises hand) and those poor struts might be a bit overworked.

hehe, you DID say that...

Overworked struts means they have insufficient damping. Insufficient damping = bouncy ride.

You made an incorrect inference from my statement. You get a bouncy ride from struts that are too soft for the springs. When one wheel goes over a bump, the swaybar only acts half as much (if that) as it would in cornering, and taxes the struts less. So, with big bars and stock strut assemblies, you have adequite dampening for bumps, and are oversprung when cornering. No bouncy ride, but i wouldn't want to drive it.


Oh, and 18"s will lessen the amount of dampening the tires do, further stressing the struts.

[BAC5.2]

How do you figure the sway bar only acts half as much when you hit a bump?

When one side compresses, and the other is unloaded, that's exactly what happens when cornering, the body just isn't rolling over it's center. The suspension is doing the same thing. That's hitting a pothole. Hit a bump with one wheel. Normally, that side would compress, and leave the other side fairly static. The car will roll over the bump smoothly, the body not getting much out of shape. Throw a huge bar on the car and drive over the same bump. NOW, you've limited the ability of the lifting wheel to act independently of the static wheel. Both sides of the car are more closely linked together, so the car humps over the bump (body following the contour of the road) instead of just rolling over it.

Look at a Jeep, for reference. When one crawls over a rock and one side tucks up while the other drops, that's the same exact motions of body roll. That's why sway bars are a NO-NO for off-roading.

Oversprung when cornering. What happens with an oversprung (underdamped) car? BOUNCY! And when turning no less! So now you have that nice benefit of having an underdamped, over sprung, when trying to negotiate bumpy turns. Your contact patch will be inconsistant, and the car's limit is severely dropped. Bad for handling. You can't disagree with this.

I agree with Scott here, 18's not lonly lessen the damping provided by sidewalls, but lots of 18's are pretty heavy. Increase in unsprung weight means worse action of the suspension.

[entirelyturbo]

Just to put some input in here, I noticed hardly any ride quality changes when I put an 18mm Turbo rear swaybar on my Legacy (nothing else changed). I think it feels firmer back there now, but nothing unpleasant.

[Legacy777]

How do you figure the sway bar only acts half as much when you hit a bump?

I don't know if half as much was just an amount he threw out there, but the anti-sway bar will not work as much when going over a bump, compared to cornering. This is true because there's going to be less wheel travel when going over a bump, compared to cornering, hence less force transferred through the anti-sway bar to the wheel that didn't travel over the bump.

[scottzg]

Yea, i just threw the number out there, but it's probably pretty close.

Josh has most of it, the other part is that when cornering weight transfers to the outside, so the inside wheel "drops down" and loads the swaybar. This doesn't happen over bumps.

Trust me.

[BAC5.2]

I'm afraid I can't trust you on your opinion that sway bars don't harm ride quality. Weight transfers ALL of the time in a car. You don't think weight transfers when you hit a bump?

Let's go to my Jeep example. Jeepers run no sway bars on the trail. Why? They limit articulation. Body roll is desired on the trail. Drive up onto a rock with one tire, and it will neatly tuck up underneath the truck, allowing the lifted tire to remain planted. Leave the sway bars ON, and when you lift a tire over the rock, the wheel does NOT tuck neatly under the fender, the bar is loaded, and the body leans over (removing weight from the higher tire and loading the grounded tire).

When you hit a bump, the wheel that hit the bump loads the bar.

Now, I'm not saying that the bar is AS effective over bumps as it is in turns, but it IS effective, and that's the point. Swaybars decrease ride comfort over un-even bumps (angled speed bumps, pot holes, diagonal washboard bumps, etc.).

While a fairly extreme bump, picture what the car would be doing if it had a sway bar. See how the body is relatively level, and the drivers side tire is neatly tucked away, and there is weight on it? With a sway bar, the bar would desperately try to keep suspension inputs the same and it would be INSANELY loaded, trying to pitch the body back to parallel with the axle. This happens, the drivers side tire becomes unloaded. Like I said, extreme situation, but it illustrates my point of weight transfer over bumps.




You will feel the difference going from an 18mm bar to a 22mm bar. It will feel EXACTLY the same on the highway and cruising and right-angle bumps, but over potholes and uneven terrain, there will be a significant stiffness increase. Like Subyluvr noticed. Not uncomfortable (no one said it WOULD be uncomfortable) but a difference, and a noticeable one.

I also found these pictures:

Same rock. Rear has no sway bar. Front has swaybar connected. Both ends are leaf sprung, and the shocks are the same length, so travel should be similar.

Look at the front tire on the rock. Looks pretty unloaded. Notice the nose pitching over. Sans sway-bar, you could probably stuff the whole setup another inch or so.



And the same shot from the other side. See the front grounded tire? The rear has no sway bar. Stuffs up nicely, doesn't it?



Part of the problem IS the rock being so big, but if the front sway bar was disconnected, the lifted tire would have much more weight on it.

No rear bar, disconnected front bar:

[scottzg]

You're missing the point. I'm saying relative to the amount of spring they provide. I'm done with this.

[BAC5.2]

I was unaware that was your point, I didn't see you mention anything about the relationship between ride-quality and springiness of swaybars. But, it's stupid to argue about anyway. I'm done with it too.

[simonasaur]

Seems that people on this forum who post alot really have a tendency to get at each other. We are all here because we have common likes, right. Thanks for the usefull info from those involed. Im pretty sure Ill go with the adjustable whiteline. I drive in the snow during the winter alot so adjustable might be the way to go. Im also thinking of selling the 18's since they rub with my car as low as it is. Maybe Ill save them for my next subaru.
Peace
Sam