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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Let's Have a Sway Bar Discussion!



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      09-06-2008, 12:03 PM   #1
Mr. 5
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Let's Have a Sway Bar Discussion!

I'm confused!
Although I might know about tuning and performance mods, I will admit that I know absolutely nothing about sway bars.
I've been reading a lot around here about sway bars, but I'm still trying to find the science behind all of it.

My questions are the following:

What is overkill?
Hotchkis makes a 32mm front and a 16mm rear, when stock is 26.5mm front and the rear is 13mm.
I noticed that UUC makes them now but is this only for the XI?

The M sport package makes a 14 mm sway in the rear and I was thinking of getting it, but would the Hotchkis be that much different?

What about sound?
I don't want my car squeaking all over the place.
Do I have to worry about that?

I would appreciate some experts to chime in on this and explain their experiences.
Thanks!
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      09-06-2008, 12:09 PM   #2
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I personally dont think they are necessary to upgrade if you get the right suspension in the car.
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      09-06-2008, 12:13 PM   #3
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I rode in my friends E92 with just H&R sways and it was a big difference in
body roll. They cant be adjusted like UUC and Hotchkis, but they are 250$ cheaper.
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      09-06-2008, 12:21 PM   #4
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Quote:
Originally Posted by S4to335 View Post
I personally dont think they are necessary to upgrade if you get the right suspension in the car.
Well, the reaosn why I'm asking is because I actually like the sport suspension on my car. I do a lot of freeway driving and I don't want to be bumping around everywhere.
I think I'm going to upgrade to the performance suspension which use the same springs as sport, but that's about it.

If I can upgrade the way the car feels throughout the turns without messing with the feel in a straight line then I'll be happy.

Quote:
Originally Posted by umcool911ok View Post
I rode in my friends E92 with just H&R sways and it was a big difference in
body roll. They cant be adjusted like UUC and Hotchkis, but they are 250$ cheaper.
This is where you got me. what do you mean they are adjustible?
I thought you just put the sway bars on and then that's it.
If you're saying that they need to be adjusted for the proper conditions then I'm not for it at all.
I want something that I can install and never look back.

How the heck would you adjust it anyway?
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      09-06-2008, 12:37 PM   #5
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I have the UUC sway bars on my front and rear (e92). They do make a huge difference in body roll and does not affect anything in a straight line... they basically just keep the car from tilting around corners, keeping you more level.

They are adjustable in that you can change the stiffness of the front and rears (more stiffness in front gives you more understeer, less stiffness gives you more oversteer -- the vice versa is true for the rear sway bar). The way this works is that the ends of the sway bar are angled at about 90 degrees and on the outside of the bend there are 3holes (on the front sway bar... there are only 2 holes for the rear). The holes are spaced about 1cm away from each other so that the first hole is closer to the bar's axis and the last hole is further away. The further away you attach the endlinks from the bar, the easier the bar can be bent (due to torque being increased as a function of radius away from the bar). Therefore, the further away you attach the endlinks from the bar, the softer the bar will behave. The closer you attach the endlinks to the bar, the stiffer the bar will behave... i know it's confusing by typing, but if you have any questions, feel free to post up or PM me and I'll do the best i can to clarify!


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      09-06-2008, 01:20 PM   #6
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my understanding of how sway bars work, in addition to what skim said, is that they essentially "tie" your suspension together. what happens in a corner is that, as one side of the car compresses, it will pull the other side to keep it more level through a turn. the possible effects are a gain in grip, thanks to the more balance of the cornering forces on the tires, or lift in the opposite tire(s) if the sway bars are too stiff
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      09-06-2008, 01:22 PM   #7
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my understanding of how sway bars work, in addition to what skim said, is that they essentially "tie" your suspension together. what happens in a corner is that, as one side of the car compresses, it will pull the other side to keep it more level through a turn. the possible effects are a gain in grip, thanks to the more balance of the cornering forces on the tires, or lift in the opposite tire(s) if the sway bars are too stiff
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      09-06-2008, 01:31 PM   #8
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Quote:
Originally Posted by Mr. 5 View Post
Well, the reaosn why I'm asking is because I actually like the sport suspension on my car. I do a lot of freeway driving and I don't want to be bumping around everywhere.
I think I'm going to upgrade to the performance suspension which use the same springs as sport, but that's about it.

If I can upgrade the way the car feels throughout the turns without messing with the feel in a straight line then I'll be happy.


One can adjust the amount of body roll with spring rates(this is what most of the racers do) and use only anti-roll bars to fine tune the balance, but that also means a bumpy ride on the rough surfaces.

The other option is to limit body roll with a balanced set of anti-roll bars. Ride quality is retained in this case. However, one can go too far with anti-roll bar that is too large and casue either end of the vehicle to loose traction. In the case of the E9x cars, adding a too stiff rear anti-roll bar only can cause the inner rear tire to lift and loose traction, and that is bad news especially without a good LSD.

Hope this helped!

Harold
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      09-06-2008, 02:10 PM   #9
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Originally Posted by HP Autowerks View Post
One can adjust the amount of body roll with spring rates(this is what most of the racers do) and use only anti-roll bars to fine tune the balance, but that also means a bumpy ride on the rough surfaces.

The other option is to limit body roll with a balanced set of anti-roll bars. Ride quality is retained in this case. However, one can go too far with anti-roll bar that is too large and casue either end of the vehicle to loose traction. In the case of the E9x cars, adding a too stiff rear anti-roll bar only can cause the inner rear tire to lift and loose traction, and that is bad news especially without a good LSD.

Hope this helped!

Harold
Well, are the Hotchkis roll bars too large?
What is considered to be too large?
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      09-06-2008, 02:11 PM   #10
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I noticed that you said noise was an issue.

My experience with the UUCs on my 335 Coupe SP is that they do tend make clunking sounds and have come loose a few time.

In their defense, They were very early units and I think I just got an off set of bushings. It's not the install as I've had 2 extremely reputable guru-types install and recheck.

I do track the car about 14 days a year so that can be a little hard on the suspension and cause the loosening.

The performance difference is really nice and I think you would be very happy

Although it's not a giant difference in handling it is definite; flatter cornering with a little better turn in.

This is my experience only.
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      09-06-2008, 02:28 PM   #11
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If you are going to be mostly street driving you could
just do the h&r sways and forget about it since they do not need
to be adjusted.
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      09-06-2008, 05:12 PM   #12
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The Hotchkis bars are hollow (lighter!), so the diameter/thickness may not comparable to the OEM or H&R bars. Even with solid bars thickness is not a perfect measure because different alloys have different compressive/tensile properties. Most manufacturers will provide some estimate of change relative to OEM.

If you are sticking with BMW springs & dampers I would probably stay with the M-sport rear sway. If you want something tighter, the Hotchkis sways w/ Bilstein PSS10s are a serious option.

If you go the latter route then you might want to consider a Hotchkis chassis brace and a front strut tower brace to keep the chassis rigid enough to handle the stiffer suspension.

My wife is usually more agreeable about mods like this than trying to argue for a tune to go quicker...
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      09-06-2008, 06:54 PM   #13
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I have H&R sways on my car...worth every penny and I've to say it made much bigger difference than getting the Eibach Prokit/Koni FSD. H&R sway bars are the same size or similar to what M3 use, although that doesn't mean much since M3 have LSD and we don't.

Many people say H&R's size (27mm F 20mm R) is overkill but IMO that's not the case at all. BMW designed all non-M cars to have natural understeer so it's safer for street driving, while all M cars are perfectly balanced for performance, that's why they have much thicker rear sway bar.
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      09-06-2008, 07:02 PM   #14
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Also, H&R's are 250$ less than the UUC or Hotchkis don't know why. Maybe
because of adjusability?
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      09-06-2008, 07:43 PM   #15
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i have heard from my frd with a E46 M3
changing sway bar might actually damage the sub frame or whatever it calls
this is what happen to my frd....the subframe is bent or damage due to the sway bar
so do we have to worry about this problem as well?
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      09-06-2008, 07:57 PM   #16
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Quote:
Originally Posted by Kit523 View Post
i have heard from my frd with a E46 M3
changing sway bar might actually damage the sub frame or whatever it calls
this is what happen to my frd....the subframe is bent or damage due to the sway bar
so do we have to worry about this problem as well?
If you find a reliable installation shop, your fine. But I would definately do your homework, because it's not an easy install.
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      09-06-2008, 08:10 PM   #17
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The guy at our BMW dealership found a way to do it without dropping the
rear subframe!!

All that needs to be done is have the sub frame just loosened and have the
sway bar angled up just right. No need to drop the sub frame
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      09-06-2008, 08:39 PM   #18
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Quote:
Originally Posted by umcool911ok View Post
The guy at our BMW dealership found a way to do it without dropping the
rear subframe!!

All that needs to be done is have the sub frame just loosened and have the
sway bar angled up just right. No need to drop the sub frame
really ? i am planning to get adjustable sway bar
this is a really good news to me
coz i have been worrying about the subframe problem
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      09-06-2008, 08:51 PM   #19
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Quote:
Originally Posted by umcool911ok View Post
The guy at our BMW dealership found a way to do it without dropping the
rear subframe!!

All that needs to be done is have the sub frame just loosened and have the
sway bar angled up just right. No need to drop the sub frame
I was actually planning on doing the install myself.
I was hoping to borrow my buddy's lift, so I think I should be fine.

Can someone explain why the rear is harder to install than the front?
I've heard this before.

What's funny is how some websites state that it's easy to install.
Now, I'm pretty handy, but this does not sound like an "easy" installation.
To me, an easy installation is something like replacing an air filter or doing an oil change.
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      09-06-2008, 08:58 PM   #20
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Quote:
Originally Posted by Kit523 View Post
really ? i am planning to get adjustable sway bar
this is a really good news to me
coz i have been worrying about the subframe problem
I don't think Advance dropped the subframe when they installed mine, they did it in less than 3 hours with 2 guys.
i never heard of anyone report subframe problem caused by sway bar, maybe a torn bushing or something like that. and what happens to E46 is pretty irrelevant since the chassis and suspension is different.
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      09-06-2008, 09:03 PM   #21
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Mr. 5 The rear is just harder because it requires more work because
of the rear subframe having to be loosened. The front is pretty much straight forward
and nothing is really in the way.
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      09-06-2008, 09:06 PM   #22
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Right now I'm trying to decide on what sway bars to get. I liked the feeling of my friends H&R's with stock suspension, but what if I want to adjust them if I start to track
my car, which I'm not sure if I am going to because I don't have any kind of cash to replace anything on it really, being a teenager means all the crap on my car has been payed for by me, well except for the car of course.

The H&R's are the thickest sway bars though and the cheapest.
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