Is it worth upgrading the rear sway bar?

[BumpinAlpine]

After reading up on the E46 suspension, a lot of people on the forums mention that upgrading the rear sway bar increases understeer. I was looking at upgrading the front sway bar to the Hotchkins 30mm bar and wondering if I should just leave the rear bar alone.

[wertyu78]

After reading up on the E46 suspension, a lot of people on the forums mention that upgrading the rear sway bar increases understeer. I was looking at upgrading the front sway bar to the Hotchkins 30mm bar and wondering if I should just leave the rear bar alone.

A stiffer rear sway bar typically induces more over-steer, as the rear end of the car will rotate faster.

[johnrando]

That's what I would have thought, oversteer with a bigger rear bar, but I've read many a post that says it induces understeer.

[wertyu78]

That's what I would have thought, oversteer with a bigger rear bar, but I've read many a post that says it induces understeer.

There are likely other factors contributing to the understeer, and perhaps, even a placebo effect.

General rule of thumb - larger rear bar, less roll = faster rotation. That's physics :)

you just reminded me, time to upload those photos from earlier this year.

[wertyu78]

There are likely other factors contributing to the understeer, and perhaps, even a placebo effect.

General rule of thumb - larger rear bar, less roll = faster rotation. That's physics :)

you just reminded me, time to upload those photos from earlier this year.

If you suffer from understeer.... there are a ton of options:

add negative camber, add toe out, add positive camber, stiffen front bar, etc. etc. etc. etc.

[derbo]

30mm front bar, stock M3 rear bar. Feels awesome. :D

[BMWCurves]

30mm front bar, stock M3 rear bar. Feels awesome. :D

Don't you have to modify the M3 rear sway bar to get it to fit on our cars?

[san]

Don't you have to modify the M3 rear sway bar to get it to fit on our cars?

I think derbo has m3 rear suspension on his Zhp...


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[slater]

Don't you have to modify the M3 rear sway bar to get it to fit on our cars?


I think derbo has m3 rear suspension on his Zhp...

yep, you need the entire M3 rear subframe assembly (with diff, axles, etc) to run the M3 rear swaybar.

i just upgraded the front to a stock M3 bar (26mm) with poly bushings and have the stock rear bar on at the moment. the front turns in much nicer. i will be putting a 20mm stock rear swaybar from an E46 vert on shortly.

peter

[Simmsled]

yep, you need the entire M3 rear subframe assembly (with diff, axles, etc) to run the M3 rear swaybar.

i just upgraded the front to a stock M3 bar (26mm) with poly bushings and have the stock rear bar on at the moment. the front turns in much nicer. i will be putting a 20mm stock rear swaybar from an E46 vert on shortly.

peter

This combination, I've heard, is a great "OEM+" upgrade.

Definitely review it!

[slater]

This combination, I've heard, is a great "OEM+" upgrade.

Definitely review it!

will do, but will be hard as i will have new springs, dampers, bushings, etc. :)

peter

[BADCLOWN]

on my old silbergrau ZHP, i had F/R H&R sways (no other mods on the car) and that thing handled on RAILS

[JeffSaysThings]

I've seen some confusing or downright wrong information floating around here regarding sway bars. Needless to say, suspension tuning is complicated and there are lots of variables that influence one another.

That being said, increasing front roll stiffness will usually increase understeer.

When I bought my car, it had a bimmerworld (ground control) front sway bar with the stock rear bar and fat rear tires (265 width). It understeered like a pig in steady state cornering. I recently installed a H&R rear bar (22mm I think?) and it really helped the car rotate. The car is more neutral (still understeers a little) in steady state cornering and will rotate with the throttle.

My previous owner did a lot of auto-x I think he chose the above setup because having a soft (or no) rear sway bar helps the car get power down without an LSD. As for me, I remedied the situation by installing an LSD AND a stiffer rear bar! The car is SO much more fun as a DD. :mwah

[NoVAphotog]

I've seen some confusing or downright wrong information floating around here regarding sway bars. Needless to say, suspension tuning is complicated and there are lots of variables that influence one another.

That being said, increasing front roll stiffness will usually increase understeer.

When I bought my car, it had a bimmerworld (ground control) front sway bar with the stock rear bar and fat rear tires (265 width). It understeered like a pig in steady state cornering. I recently installed a H&R rear bar (22mm I think?) and it really helped the car rotate. The car is more neutral (still understeers a little) in steady state cornering and will rotate with the throttle.

My previous owner did a lot of auto-x I think he chose the above setup because having a soft (or no) rear sway bar helps the car get power down without an LSD. As for me, I remedied the situation by installing an LSD AND a stiffer rear bar! The car is SO much more fun as a DD. :mwah
Interesting, what'd you do about the tires...and the pig? [emoji14]

[Vas]

Bacon

[rkneeshaw]

I've seen some confusing or downright wrong information floating around here regarding sway bars. Needless to say, suspension tuning is complicated and there are lots of variables that influence one another.

That being said, increasing front roll stiffness will usually increase understeer.

When I bought my car, it had a bimmerworld (ground control) front sway bar with the stock rear bar and fat rear tires (265 width). It understeered like a pig in steady state cornering. I recently installed a H&R rear bar (22mm I think?) and it really helped the car rotate. The car is more neutral (still understeers a little) in steady state cornering and will rotate with the throttle.

My previous owner did a lot of auto-x I think he chose the above setup because having a soft (or no) rear sway bar helps the car get power down without an LSD. As for me, I remedied the situation by installing an LSD AND a stiffer rear bar! The car is SO much more fun as a DD. :mwah

This is great feedback.

I think there is a lot of confusing information on the topic but what you posted is pretty clear.

I would propose that "balance" is best measured in steady-state cornering, not how the car turns as you chuck it into a corner which can be very subjective and depends a lot on driver inputs as much as suspension components.

I've always been very confused by reports that a larger M3 front bar alone helps reduce understeer, because its counter to conventional wisdom. Normally a larger bar in the front will increase understeer, and a larger rear bar will increase oversteer.

I've also been confused as to why companies like Eibach, H&R, Turner, hotchkis, etc all create a sway bar kit (front and rear) that increase the stock bar sizes by pretty much the same amount. If our cars really need a larger bar for proper balance, I would think you would see only a marginally smaller rear bar and a much larger front bar in these kits.

What size is your ground control bar up front?

[derbo]

This is great feedback.

I think there is a lot of confusing information on the topic but what you posted is pretty clear.

I would propose that "balance" is best measured in steady-state cornering, not how the car turns as you chuck it into a corner which can be very subjective and depends a lot on driver inputs as much as suspension components.

I've always been very confused by reports that a larger M3 front bar alone helps reduce understeer, because its counter to conventional wisdom. Normally a larger bar in the front will increase understeer, and a larger rear bar will increase oversteer.

I've also been confused as to why companies like Eibach, H&R, Turner, hotchkis, etc all create a sway bar kit (front and rear) that increase the stock bar sizes by pretty much the same amount. If our cars really need a larger bar for proper balance, I would think you would see only a marginally smaller rear bar and a much larger front bar in these kits.

What size is your ground control bar up front?

I think the problem is that it seems the internet wants to put it as a rule of thumb that stiffer front bar = understeer, stiffer rear bar = oversteer. suspension tuning is a fine art and it's almost a black art where the information is never transferred well on the internet. With a stiffer bar in rear, yes you do increase oversteer, but you also decrease high speed cornering stability. In an AutoX car, it doesn't matter too much as they don't get that fast in the parking lot. On a street car where there are numerous different types of situations, I think the anti-roll bar needs to be sized properly but not be too large.

My car has 448/560 spring rates with a 30mm front H&R sway bar and the OE M3 rear sway bar + LSD. My camber is set to -3 in the front and -2 in the rear. With a larger front bar, I felt a better stability during high speed corners (over 70mph corners) at the track. However I noticed for slower speed corners like hairpins on a mountain road, it does have slightly more understeer. I granted have a track car so I'll take that compromise any day.

[05Imola]

I installed the TMS sway bars this week. I installed the front seat bar first with adjustable links. The car immediately felt flatter but the car understeered a lot at lower speeds. I installed the rear a few days ago with adjustable links again. Car is so more balanced. I have it on the middle hole and I might make it softer for the winter. Car still has some roll but that's because I'm running an H&R Touring cup kit. Perfect balance for street in my opinion

[johnrando]

There are likely other factors contributing to the understeer, and perhaps, even a placebo effect.

General rule of thumb - larger rear bar, less roll = faster rotation. That's physics :)

you just reminded me, time to upload those photos from earlier this year.
Yes, post those pics. I'd also like to do some rear suspension work sometime with you.

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[BumpinAlpine]

Thanks for all the input.

I have a set of BavAuto Sway bars which are solid bars 27mm front and 23mm rear and they are non adjustable. Suspension wise, I'm running the Koni FSD/Eibach Pro kit.
The BavAuto bars helped reduce some roll but I feel like I could do better. I am considering in keeping the rear bar as is at 23mm and getting a Hotchkis 30mm bar up front.

Any thoughts on this?

[terraphantm]

I've always been very confused by reports that a larger M3 front bar alone helps reduce understeer, because its counter to conventional wisdom. Normally a larger bar in the front will increase understeer, and a larger rear bar will increase oversteer.


What the conventional wisdom misses is that the E46 (and pretty much any car with a macpherson strut front suspension) has a crap camber curve. So the more the spring compresses, the more positive the camber becomes. A stiff front bar will limit that suspension travel, and reduce how "positive" the camber goes.

[Simmsled]

What the conventional wisdom misses is that the E46 (and pretty much any car with a macpherson strut front suspension) has a crap camber curve. So the more the spring compresses, the more positive the camber becomes. A stiff front bar will limit that suspension travel, and reduce how "positive" the camber goes.

Nail on head.

Where the understeer comes in is after the fat front bar saturates the front tires and grip goes to the meat on the rear wheels.

While those front tires have grip though... Racekor

[RedAtom]

Great thread, I am thinking of upgrading the stock bars on my ZHP to M3 front and vert rear sway. Has anyone here run this setup and can provide some feedback on feel?

Thanks all!

[slater]

Great thread, I am thinking of upgrading the stock bars on my ZHP to M3 front and vert rear sway. Has anyone here run this setup and can provide some feedback on feel?

Thanks all!

i run that combo, but i made a lot of changes at once. hard to quantify, sorry.

[BMWCurves]

Great thread, I am thinking of upgrading the stock bars on my ZHP to M3 front and vert rear sway. Has anyone here run this setup and can provide some feedback on feel?

Thanks all!

E46 M3 front sway bar and E46 330Cic rear is one of the options I have played with as well. I think I would prefer the moderate upgrade compared to a more aggressive set of sway bars like UUC (http://store.uucmotorwerks.com/swaybarbarian-sway-bar-set-for-1999-2005-e46-330-328-325-323-all-variants-except-xi-p54.aspx) (Front: 27mm/Rear: 23.8mm), TMS (https://www.turnermotorsport.com/p-339019-e46-323325328330ici-turner-motorsport-frontrear-2721-sway-bar-upgrade/?pdk=AQEB) (Front 27mm/Rear: 21mm), Hotchkis (http://www.hotchkis.net/product/1999-2006-bmw-e46-sport-sway-bars-from-hotchkis-sport-suspension/?mk=31&yr=2005&md=181&sm=1117) (Front: 30.2mm/Rear: 25.4mm), etc.

Stock sway bar sizes for the ZHP are front 23.5mm, and rear bar is 18mm, I believe. Someone can correct me if I'm wrong.
I'm not sure what the stock E46 M3 sway bar sizes are, or the rear of a non-M E46 vert.

[704sw]

I'm not sure what the stock E46 M3 sway bar sizes are, or the rear of a non-M E46 vert.

I think the M front is 26.5 so everyone just calls it 27? That's what I'm looking at up front, with a Cic rear or a 21 non-adjustable.

[RedAtom]

Those sound pretty good. I am not looking to get too aggressive just have the car stay a little flatter in the curvy bits.

Thanks for the sound off guys!

[BMWCurves]

I think the M front is 26.5 so everyone just calls it 27? That's what I'm looking at up front, with a Cic rear or a 21 non-adjustable.

Ah, so the TMS sway bar set is basically that setup, just with adjustability? Interesting...

*wallet cries tears of sadness*

[Vas]

Tms is the same as h&r

[BMWCurves]

Tms is the same as h&r

Same as in the same part or the same size? And are the TMS the same as the ECS units seeing as ECS now owns TMS?

[704sw]

Ah, so the TMS sway bar set is basically that setup, just with adjustability? Interesting...

*wallet cries tears of sadness*

Yep. I'm only going with the OE M3 sway because I'm not worried about minor adjustability. Plus they're readily available for sub $100 in great condition.

And I think the Cic is 20 rear.

[slater]

Yep. I'm only going with the OE M3 sway because I'm not worried about minor adjustability. Plus they're readily available for sub $100 in great condition.

And I think the Cic is 20 rear.

correct, Cic rear is 20mm.

i got both M3 front and Cic rear on ebay for $100 shipped, combined. of course, i spent about $70 shipped on poly bushings, but still - that's good economics. ;)

[BMWCurves]

What seller magically had this combo for sale in great condition for $100, hmm? LIES

[RedAtom]

Used stock units are definitely cheap. Don't think it is not a factor in my decision!!!

Odd to see those two packaged together for so cheap though.

Wanna sell em? ;)

[Aeternalis]

Ooh. I've been waiting for a thread like this! When the time is right, I plan on moving to this setup:

25mm front stabilizer from the 3.0 Z4 w/ M Suspension (31351096364)
20mm rear stabilizer from the E46 CiC mentioned above (33556751267)

Just a touch more aggressive than stock to firm up the handling for my 100% street car. Also 100% Genuine parts.

Here's the bushings in case anyone else might be interested in it.

20mm - 33551096669
25mm - 31351096365

[slater]

What seller magically had this combo for sale in great condition for $100, hmm? LIES

different sellers... M3 front was $45 shipped, 20mm rear was $55 shipped. :)

[BMWCurves]

Thanks for the info, fellas :thumbsup

[Dave1027]

If it's reduction of understeer you're after, the easiest way to do it is to reduce (or remove completely) the rear toe in.

Also, I'm going to have to disagree with what terraphantom posted about front camber reducing when the spring compresses. Without a doubt, fornt negative camber increases as the spring compresses. That's why people who slam their cars usually end up with too much neg camber.

[704sw]

different sellers... M3 front was $45 shipped, 20mm rear was $55 shipped. :)

Well, sir, I didn't get as good of a deal as you, but I'm still pleased. $130 for both. Cic is local, M3 front bar I'm getting next weekend in DC when I'm up there for some playoff hockey.

[BMWCurves]

Well, sir, I didn't get as good of a deal as you, but I'm still pleased. $130 for both. Cic is local, M3 front bar I'm getting next weekend in DC when I'm up there for some playoff hockey.

Interested in your thoughts once they are installed. Thoughts on the sway bars, not like, your views on the futility of life or the screenplay you've been working on for the last seven years.

[704sw]

Interested in your thoughts once they are installed. Thoughts on the sway bars, not like, your views on the futility of life or the screenplay you've been working on for the last seven years.

Don't criticize my screenplay, alright? It's going to tug at the heartstrings of every man, woman, and child.

It's going to be part of a pretty big suspension overhaul, so I suspect my thoughts will be along the lines ofhttps://uploads.tapatalk-cdn.com/20170408/765e7add8e2a5787ef2784c339cf35fd.jpg

[BMWCurves]

Tug at their heartstrings...because it will cause cardiac arrest in anyone that reads/hears it? I jest...

Reminds me of the world's funniest joke though:


https://www.youtube.com/watch?v=WwbnvkMRPKM&t=13s

And now for something completely different: what are you refreshing your suspension with? Get out your best hammer, summon your inner Clarkson, and get to work:

http://i.imgur.com/WRVGIN1.gif

Okay, I think that's enough procrastination for me