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Suspension & Braking Forum by BimmerWorld
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Old 04-19-2013, 10:15 PM   #1
jlgone
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Help with sway bar settings

I am installing TMS (H&R) sway bars on my e46 330 convertible with OE sport springs and Koni FSDs. This is for a daily driver, not track.

The non-M convertibles have thicker sways than coupe or even ZHPs with factory sport convertibles using 24mm Front and 20 mm Rear; the difference in the rear is 20 mm for vert and 18 mm for non-M coupe, presummably due to more weight in the rear. The TMS sways will be 3 mm thicker than stock in the front but only 1 mm thicker in the rear. TMS are adjustable and they recommend installing the front on firmest (of 2 possible settings) and the rear on the middle firmness (of 3 possible settings). Given that my vert rear sway diameter will only be increasing by 1 mm I am thinking I should set the rear on full firm as well. I am assuming TMS's recommendation is for coupes which would be going from an 18 mm to 21 mm bar, so the full firm should keep things relatively the same for my convertible.

My only reservation is the autocrossers often use a thick front bar and stock rear bars or even no rear bar. On the other hand, UUCs are 26 F 24 R and Dinan 24F 22 R so their rear is relative thick vs the front - so who is right??? Should I try to mimic the factory relationship between F and R by setting the relatively thin rear bar to firm, or set the rear in the middle setting per TMS recommendations?? I just want the best handling street set- up.

Thanks for any advice!!
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Old 04-19-2013, 11:12 PM   #2
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If it's only 1mm larger, you can go ahead and set it to the firmest, otherwise you may not feel much difference in the rear. Autocrosser need it softer to avoid lifting the inside wheel on turns, but for street (to me) firm feels better because it reduces sway and improves turn in. Have fun!
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Old 04-20-2013, 10:23 PM   #3
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Should I set the front to softer setting and the rear to firmest? I never understood why some bars are much thicker in front (eg, h&r and Eibach 27 F 21 R) and UUC and Dinan were about the same thickness front and rear.

Should I have the front stiffer for the street?
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Old 04-21-2013, 09:05 PM   #4
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The front doesn't have to be on the firmest setting because the diameter is 3mm larger already. It's pretty easy to change the setting, so you can experiment with that. The science behind swaybars is tricky, bigger bar on the front can help traction in the back.
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Old 04-22-2013, 12:27 PM   #5
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It sounds to me that you and others here really need to read up on what the function of the sway bar is and how the sizes impact handling. You are asking the questions AFTER buying the bars! Basically the OEM sizes are set up for understeer. That is large front and small rear bar. The H&R 27/21 maintains this factory understeer. YUCK! I have factory front and H&R 21 rear for neutral handling on my ci and have tried a few different suspension setups. Recommend H&R for factory understeer and UUC for otherwise OEM struts/springs and a set up like Dinan or mine for say Bilstien sports and stiffer H&R springs. So, that being said I would go soft front and stiff rear with thos bars. Try different settings and see where you like it!
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Old 04-22-2013, 07:45 PM   #6
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I actually did quite a bit of research before buying. Fitment limited my choices.

All of the sway bars are designed for coupes; convertible have different bars from the factory and info on aftermarket suspensions for convertibles is difficult to find. There are support braces in the rear and the rear of the car is heavier.

Hotchkis won't fit a convertible (confirmed directly with Hotchkis) and UUC have questionable fitment even on coupes (tabs reported to hit axle shafts) and, unlike the H&R/TMS which have teflon bushings, UUCs require lubrication.

I picked TMS (same as H&R but cheaper) since I have faith in their knowlegde of BMW 3 series and I was able to verify the fit without problems from other vert owners.

My confusion is based on conflicting messages across many threads, including this one - Stiffer front or stiffer rear?!? TMS says stiffer in the front so that's still where I'll go with the front, especially since most people say the front bar matters more for handling. Given the back is only 1 mm thicker I will go full firm in the rear.

Last edited by jlgone; 04-22-2013 at 08:10 PM.
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Old 04-22-2013, 09:49 PM   #7
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You'll find the setting you like most once you play with it. The reason why I
love swaybars is because you can improve handling/reduce body roll without
making the ride firmer, i.e. changing springs and shocks.
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Old 04-22-2013, 10:18 PM   #8
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Swaybars and how they are set are relative to the driving conditions and speed at which the car is driven. Set bar feel for the most common conditions you encounter and you'll be happy. There is not a one size fits all, hence the different bar sizes. Driver style and weight also greatly contribute to the bar required. If you straight line brake the bar setting will be different than if you tend to trail brake.

Long story short, asking people what you should do may or may not get you close, but only you can set it for you.
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Old 04-22-2013, 10:42 PM   #9
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Who told you that autocrossers use no rear bar?

I have my uuc bars set on full stiff rear and medium front I believe. I'm not impressed so I'm going to have to adjust them soon. I need more oversteer and have no accomplished that yet.
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Old 04-22-2013, 11:27 PM   #10
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There are many confusing posts on sways. Some say the front strut suspension geometry benefits from a stiff bar, with the rear reducing underteer as it gets stiffer. Perhaps I was mistaken and it was track cars rather than auocross where they didn't use any rear bar. Others say stiffen the rear with a soft front to eliminate understeer.

The TMS bar is considerably thicker in the front vs rear (27 F 21 R) and TMS still recommends full stiff in front and middle setting in the rear, which should give MORE oversteer than stock ( the opposite of what you 'd think if you you only thought of eliminating understeer ). There must be some truth to the point of a stiffer front bar helping Reduce underteer in the e46?

I will follow TMS recommendation of front stiff and also add stiffness to the rear finitially, then see what happens if I soften the front.

Last edited by jlgone; 04-23-2013 at 07:03 AM.
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Old 04-22-2013, 11:54 PM   #11
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Stiffer front bar will increase under steer. Simple as that.
Away bars do not increase overall grip. They fine tune the in turn characteristics of the car.
Refer to this to understand what does what.
http://store.uucmotorwerks.com/artic...ybar_setup.htm

I'm still not convinced that adjusting them will eliminate my understeer which sucks. But I'll see after I adjust them.
There's no need to have oversteer for road use btw. Don't seek that. For road use I'd want as little understeer as possible with no oversteer.

My e30 has almost neutral handling with a hint of oversteer and sweet Jesus that handling is amazing. It has stock sway bars. I think it's the way the rear trailing arms are designed.
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Old 04-23-2013, 01:25 AM   #12
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Originally Posted by peytonracer4 View Post

My e30 has almost neutral handling with a hint of oversteer and sweet Jesus that handling is amazing. It has stock sway bars. I think it's the way the rear trailing arms are designed.
Was? Ein e30 ohne Übersteuern?
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Old 04-23-2013, 06:05 PM   #13
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Quote:
Originally Posted by peytonracer4 View Post
Stiffer front bar will increase under steer. Simple as that.
Away bars do not increase overall grip. They fine tune the in turn characteristics of the car.
Refer to this to understand what does what.
http://store.uucmotorwerks.com/artic...ybar_setup.htm

My e30 has almost neutral handling with a hint of oversteer and sweet Jesus that handling is amazing. It has stock sway bars. I think it's the way the rear trailing arms are designed.
Please stop you're making me want to buy an E30!
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Old 04-23-2013, 06:06 PM   #14
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Was? Ein e30 ohne Übersteuern?
Warum?
Ist das nicht moglich?
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Old 04-23-2013, 08:05 PM   #15
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Not sure how you could say sway bars don't increase overall grip. You're distributing the cornering force more evenly from the outside to inside tires, so it should definitely increase grip. The downside is that your independent suspension becomes less independent...hence why cars like the MP4-12C are going to active dampers that adjust on the fly, eliminating the need for sways altogether. Our cars don't have that.

Front sway should make understeer more prominent, but that's not necessarily the case in my experience. Probably something to do with the relatively uncommon Macpherson front and multi-link or trailing-arm rear suspension designs on BMWs. Setup tips for cars with 4-wheel double-wishbone setups need not apply. Different animals.

Plenty of autocrossers ditch the rear bar to keep the inside tire from lifting mid-turn...lots of cars also unload the diff when that happens, if it's open or a Torsen-type. BMW LSDs are clutch type, so this happens less...though it still slows you down.

If you're serious about going fast, play with settings until you find the perfect neutral for your driving style. In a DD that doesn't see any angry driving, who cares? Put them on, set it and forget it.
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Old 04-23-2013, 08:08 PM   #16
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You say you want the best handling street car?

But you state that you car is daily driven and not on track. Doesn't the "best handling street car" aspire to be a race car? It is all in how much you are willing to sacrifice to get to the next level, and the next.

Also, I autocross heavily and very competitive. Top 3 in one of the fastest classes in my BMWCCA chapter. There a quite a few people and people that are faster than me that delete the rear sway bar. Deleting the rear sway bar in itself will cause more body roll, but we delete the rear sway bar and add linear springs with quality dampers, springs usually around #500. The purpose of this is to increase traction throttling out of a corner. You give gas out of a corner, it transfers the weight to the back of the car where you need it to power out faster and much earlier. The car almost "squats".

This however is not ideal for a street car. Autocross suspense settings and racetrack suspension settings are not even similar. You have to figure out what you want. Do you want autocross handling or race car handling?

If you want race car handling, I would start with firm on front and middle on rear. If they are adjustable, then you can tweak it to your liking after you drive it around for awhile. I have no experience with a convertible so maybe there is some wisdom to starting out with firm in the rear since you do have more weight over the rear axle.
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Old 04-23-2013, 10:56 PM   #17
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I might have found the answer as to why H&R and Eibach have relatively thinner rear sway bars vs UUC, Hotchkis, etc. They are TUV approved and apparently that means they have to fit the rear stock mounting brackets without modification. Since the thicker "American made" bars won't fit on a vert it's somewhat of a mute point, but that would explain the fundamental differences between manufacturers in size ratio front to rear.

As for whether I want a racer or autocrosser, actually I don't want either. I want a compliant ride with better than stock handling on average quality roads, not a race car that excells on the track but handles worse than a stock suspension on imperfect roads. I didn't want to lower it so that meant I couldn't go with firmer spings. Hopefully the OE sport springs, Koni FSDs and thicker sway bars will give me an ideal street set up ( that obviously would not be as good as other set-ups on the track or for autocross). I'll report back as soon as they 're installed.
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Old 05-01-2013, 08:32 PM   #18
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I set the front and rear sway bars at full stiff and it was great - helped considerably with body roll and less understeer.

The Koni FSDs with OE sport springs and stiffer sways turned out great set up for a daily driver. It rides better with my 18s than the stock sport suspension did with 17s, and handling is considerably better than stock as well; the FSDs did what Koni promised they'd do.

It was a little strange at first because you are more isolated and don't feel every little pebble or imperfection in the road, but "road feel" is only good up to a point. The car is much smoother to drive and I am more confident and feel more control since the car is more planted and stable - I find myself driving considerably faster since I am accelerating through the gears rather than worrying about every man-hole cover ahead of me. It is much more enjoyable and I highly recommend this set up for daily drivers.

Last edited by jlgone; 05-01-2013 at 08:32 PM.
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Old 05-01-2013, 08:49 PM   #19
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Sounds great! I agree, 17"s are perfect, bigger wheels actually slow you down because you worry about potholes more. Enjoy!
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Old 05-11-2013, 11:06 PM   #20
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Sways are mostly a waste. They add spring rate and should be used to fine tune your suspension setup. So if you haven't done the tuning and setup...you're wagging the dog.

But I would think you would want the front softer and the rear stiffer for auto-x.
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