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      09-01-2017, 03:43 AM   #1
Lancelot
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Anti-roll (Sway) Bars Options study

I've put together a table of the available ARBs for our platform, BMW has quite a lot of options depending on engine, suspension, M Sport, M Adaptive or standard.

In a nutshell:
- 6 cyl get weaker front bars than 4 cyl engines
- M Sport has slightly stronger bars front and rear
- 440i LCI have stronger bars (same as M235i) than non-LCI 435i
- Xdrive have weaker front bars but same rear bars.

Aftermarket:
I've tried the H&R but they're too stiff on the rear.
I've now put on the M235i bars now and they're too weak on the front.
The sweet spot is probably the KW or Eibach, which I might try next.
(I always put bars in pairs because they're designed as pairs)

Some vendors (Hotchkis, Dinan) have hollow bars so you can't directly compare diameters with plain, non-hollow bars, hollow bar will be weaker than plain for same outer diameter.

Hope this helps...
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      09-01-2017, 11:33 AM   #2
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Quote:
Originally Posted by Lancelot View Post
I've put together a table of the available ARBs for our platform, BMW has quite a lot of options depending on engine, suspension, M Sport, M Adaptive or standard.

In a nutshell:
- 6 cyl get weaker front bars than 4 cyl engines
- M Sport has slightly stronger bars front and rear
- 440i LCI have stronger bars (same as M235i) than non-LCI 435i
- Xdrive have weaker front bars but same rear bars.

Aftermarket:
I've tried the H&R but they're too stiff on the rear.
I've now put on the M235i bars now and they're too weak on the front.
The sweet spot is probably the KW or Eibach, which I might try next.
(I always put bars in pairs because they're designed as pairs)

Some vendors (Hotchkis, Dinan) have hollow bars so you can't directly compare diameters with plain, non-hollow bars, hollow bar will be weaker than plain for same outer diameter.

Hope this helps...
While that is true, a slight increase in the size of a hollow cylinder results in a much stronger structure than the solid. 1" vs 1.125 hollow, the hollow was something like 128% stronger at 70% of the weight. Also, with the way circles work, a few more mm in diameter with a hollow structure may not be as light as you are thinking. There's a dramatic increase in circumference.
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      09-01-2017, 12:21 PM   #3
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Indeed, for those who are more math inclined the stiffness is calculated as a proportional to (D^4 - d^4) where D = outer diameter and d = inner diameter (and d = 0 if the bar is plain), while the weight is proportional to (D^2 - d^2).
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      09-05-2017, 03:16 PM   #4
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Interesting thread. So any idea which is stiffest? I would assume it's between H&R (28,20mm solid) versus AFE (32,29mm hollow).
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      09-06-2017, 02:41 AM   #5
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Quote:
Originally Posted by DSH7 View Post
Interesting thread. So any idea which is stiffest? I would assume it's between H&R (28,20mm solid) versus AFE (32,29mm hollow).
To be able to answer the question there is one last parameter: the lever arm length. Basically if the arm is shorter the bar is made stiffer.

And to make it a little more complex, most aftermarket parts are adjustable at the front, sometimes at the back like Dinan.

I'll try to update this table with the info I can find on this to try to paint the full picture.

Data I have for the 6 cylinders:
- KW and Eibach have front lever arm lengths 250 and 270mm (two way adjustable each side = 3 possible settings - Short/Short, Short/Long, Long/Long)
- H&R have lever arm lengths 250 and 265mm for the 6 cylinder version

All 3 are 150mm at the back.
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      09-06-2017, 06:54 PM   #6
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Is it difficult to put a front bar on these cars? (Xdrive). I know in my Mini Cooper, it would involve dropping entire front subframe.
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      09-07-2017, 08:13 AM   #7
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Yes BMW has adopted the same architecture on the F2x/F3x subframes, so quite a pain indeed, although my shop has done that quicker last time, altogether I was there for 5 hours for 2 anti-roll bars, rear subframe bushings, intercooler and downpipe.
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      09-07-2017, 09:20 PM   #8
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I just got my car on Tuesday (2017 f31) and am on the lookout for whatever the consensus is on a good anti roll bar setup to tame the xdrive body roll. Coming from a Mini and then a Focus ST, it was actually kind of alarming..
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      09-08-2017, 03:23 AM   #9
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The difficulty with bars is finding the right balance between taming roll and keeping suspension independence: with bars that are too stiff, potholes and similar bumps will upset the entire car balance, instead of leaving the single wheel / damper absorb the shock, it will be transmitted to the entire body.

Springs and coilovers do not have the same inconvenience so it's a better place to start in my opinion, and if not enough then use bars as a stage 2.
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      09-08-2017, 08:25 AM   #10
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do you have to drop the exhaust to install front an rear ARBs on an xdrive? (435)
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      09-08-2017, 08:45 AM   #11
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Quote:
Originally Posted by Insane435 View Post
do you have to drop the exhaust to install front an rear ARBs on an xdrive? (435)
Yes for the rear but that takes literally 5 minutes.
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      09-08-2017, 09:37 AM   #12
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Quote:
Originally Posted by Lancelot View Post
Yes for the rear but that takes literally 5 minutes.
5 mins for normal people, my exhaust barely fits (xdrive problems) I cant imagine how much work i would be adding to realign the whole damn thing.
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      09-08-2017, 10:04 AM   #13
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Quote:
Originally Posted by Insane435 View Post
do you have to drop the exhaust to install front an rear ARBs on an xdrive? (435)
Quote:
Originally Posted by Lancelot View Post
Yes for the rear but that takes literally 5 minutes.
Dropping the subframe is the most challenging part. That takes a bit of time.
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      09-19-2017, 09:18 AM   #14
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Is there a good DIY out there for dropping the rear subframe?
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      09-19-2017, 09:44 AM   #15
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Quote:
Originally Posted by AshlandTE87 View Post
Is there a good DIY out there for dropping the rear subframe?
I found the Dinan install guide for their anti roll bars to be good
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      09-29-2017, 02:37 PM   #16
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Quote:
Originally Posted by Lancelot View Post
I found the Dinan install guide for their anti roll bars to be good
I'll second this, just installed a set of Megan Racing sway bars on my 335. The Dinan instructions are excellent, but make no mistake the install is a huge pain in the ass. The rear is relatively easy, but maneuvering the front bar into place took some time.
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      09-30-2017, 08:45 AM   #17
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Quote:
Originally Posted by Niart906 View Post
I'll second this, just installed a set of Megan Racing sway bars on my 335. The Dinan instructions are excellent, but make no mistake the install is a huge pain in the ass. The rear is relatively easy, but maneuvering the front bar into place took some time.
You had access to a lift and transmission/diff jack right?
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      09-30-2017, 09:47 AM   #18
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Doesn't the type and condition of the swaybar bushings have some degree of impact on the bar performance (i.e. Rubber vs polyurethane, etc)?
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      10-02-2017, 11:46 AM   #19
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Quote:
Originally Posted by Lancelot View Post
I found the Dinan install guide for their anti roll bars to be good
Thanks! Yeah, it does look pretty comprehensive upon review.
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      10-12-2017, 02:41 PM   #20
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Trying to figure out which ARBs to put on my xdrive, you think the 440i LCI bars would work/help with body roll?
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      10-12-2017, 11:31 PM   #21
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Yes or m135i/m140i ; probably best to start with springs or coilovers.
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      10-12-2017, 11:57 PM   #22
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Already have Dinan springs and shockware, body roll still there.
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