BMW 1 Series Coupe Forum / 1 Series Convertible Forum (1M / tii / 135i / 128i / Coupe / Cabrio / Hatchback) (BMW E82 E88 128i 130i 135i)
 





 

Post Reply
 
Thread Tools Search this Thread
      08-06-2015, 12:21 PM   #1
E90ALLMANUAL
Private
13
Rep
90
Posts

Drives: E90/328i/no sunroof
Join Date: Dec 2013
Location: Alabama

iTrader: (0)

Rear sway bar disconnect

Has anyone disconnected their rear sway bar for autocross duty? Did it reduce understeer or it was too loose?
Appreciate 0
      08-06-2015, 09:09 PM   #2
lowside67
Second Lieutenant
90
Rep
221
Posts

Drives: 2011 BMW 128i
Join Date: Apr 2015
Location: Vancouver, Canada

iTrader: (0)

Disconnecting the rear swaybar will decrease rear roll stiffness which will likely have the exact opposite effect of what you are describing. Less rear roll stiffness most likely equals more understeer/less loose.

Mark
__________________
Appreciate 0
      08-07-2015, 01:24 AM   #3
spxxx
Boost
spxxx's Avatar
343
Rep
2,493
Posts

Drives: 135i M-Sport
Join Date: Feb 2014
Location: Valley of Silicon, CA - United States

iTrader: (7)

Quote:
Originally Posted by E90ALLMANUAL
Has anyone disconnected their rear sway bar for autocross duty? Did it reduce understeer or it was too loose?
No sway bar would generally cause more understeer
__________________
E82 1M Clone "Racecar"
E46 M3 "Driveway Car"
E92 M3 "Street Car"
Appreciate 0
      08-07-2015, 10:44 AM   #4
alpho
New Member
8
Rep
26
Posts

Drives: AW 135i
Join Date: Mar 2015
Location: Illinois

iTrader: (0)

Disconnecting the rear sway bar makes no discernible difference from the stock bar. Connecting a bigger bar with no LSD will make it more twitchy, slower.
Appreciate 0
      08-07-2015, 03:02 PM   #5
E90ALLMANUAL
Private
13
Rep
90
Posts

Drives: E90/328i/no sunroof
Join Date: Dec 2013
Location: Alabama

iTrader: (0)

Is this real life experience or are you guys assuming?

When I had my Miata, disconnecting the rear sway bar made the car rotate better. I know they are different cars but they are both RWD.
Appreciate 0
      08-07-2015, 04:11 PM   #6
YarkoDrives
Private
6
Rep
65
Posts

Drives: 135is 98FS, 128i, 335xi,
Join Date: May 2015
Location: CO

iTrader: (1)

I'm going to run a few events with one rsb end link removed.

135i oem open diff.

I have a very loose alignment for autocross. 0 toe in rear. BMW Performance Springs and fsb.

the back end is manageable, but not quite predictable.

1. there's a limit where the backend comes out more suddenly than it's slip had indicated up to that point. (oem rear arms/bushes don't help but they should feel linear). the oem endlinks could be to blame.

2. sometimes I get snap oversteer (in the opposite direction from load). this is very much a symptom of having a rsb. (this may be aggravated by EDL/yaw sensor overload/safety)

Removing the RSB should help with both of these:

more roll in the back should solve 1. by giving a sooner but linear feel up to the limit of traction (or to the trailing-arm deflection:bind:snap).

should solve 2 by letting the inside wheel stay more on the ground, though it will have less weight on it.

Last edited by YarkoDrives; 08-07-2015 at 04:22 PM.
Appreciate 0
      08-07-2015, 05:13 PM   #7
YarkoDrives
Private
6
Rep
65
Posts

Drives: 135is 98FS, 128i, 335xi,
Join Date: May 2015
Location: CO

iTrader: (1)

last event with a RSB. snap oversteer, as I tried to correct out of the spin at end of video.

Appreciate 0
      08-07-2015, 10:17 PM   #8
fe1rx
Lieutenant
465
Rep
547
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by YarkoDrives View Post
last event with a RSB. snap oversteer, as I tried to correct out of the spin at end of video.

That was power oversteer, i.e. due to aggressive throttle input. It occurred right after an aggressive gear shift broke the rear traction.

Oversteer is not your problem, understeer is. You are driving at very high front slip angles and are overdriving your car. It only oversteers when provoked.

I have tried disconnecting the OE rear bar on a skid pad (logging lateral g, and steering angle to get understeer gradient). With fairly stiff springs on coil-overs I could not detect any difference with the bar disconnected. With softer springs, more of the total roll stiffness comes from the bars, so it might make a small difference in your case, but it would be moving your handling more towards understeer in that case, which won't help the root problem.

Beware when disconnecting one end link, the bar may rub on the drive shaft boot at certain roll angles and one-wheel bump conditions.
Appreciate 1
      08-07-2015, 10:33 PM   #9
The Wind Breezes
Major
397
Rep
1,329
Posts

Drives: 135i N55 DCT
Join Date: Apr 2015
Location: USA

iTrader: (0)

One thing I notice is you're not yet used to steering the car with the throttle. Even a stock car will easily do what you demonstrate if driven improperly at the limit. A tip: excessive steering wheel input will actually increase understeer beyond the point where more wheel doesn't cause the car to turn in more.
Appreciate 0
      08-08-2015, 11:38 PM   #10
Kgolf31
Brigadier General
Kgolf31's Avatar
365
Rep
4,569
Posts

Drives: 2007 Z4MC, 2012 128i
Join Date: Sep 2008
Location: Ohio

iTrader: (4)

19mm bar. No issues

Appreciate 0
      08-22-2015, 06:59 AM   #11
katsooba
First Lieutenant
katsooba's Avatar
52
Rep
318
Posts

Drives: bmw 135i
Join Date: Apr 2012
Location: Israel

iTrader: (0)

Kgolf that a heck of an attack mode! you're on fire
__________________
135i N55 / KW V3 / JB4 S2 + MHD Flash / CP-E 5" DP / CP-E charge pipe / CP-E 7" FMIC / M3 Subframe Bushings / Powerflex Diff and rear shock mount bushes / M3 front control arms / M3 Rear control arms / MFactory LSD / KW 28mm front antiroll / Eibach rear 15mm bar

Last edited by katsooba; 10-16-2015 at 11:19 AM.
Appreciate 0
      08-24-2015, 11:22 AM   #12
chris82
Brigadier General
chris82's Avatar
United_States
391
Rep
3,167
Posts

Drives: around town (Philadelphia)
Join Date: Aug 2012
Location: a black coupe

iTrader: (6)

Garage List
2008 BMW 128i  [5.00]
take it off and see what you like better
Appreciate 0
      08-26-2015, 10:05 AM   #13
E90lova
New Member
4
Rep
29
Posts

Drives: E46
Join Date: Jul 2013
Location: Boston

iTrader: (0)

Quote:
Originally Posted by E90ALLMANUAL View Post
Has anyone disconnected their rear sway bar for autocross duty? Did it reduce understeer or it was too loose?
This is an E30 thing. I tried this on my 86 325e and it actually made the car very neutral but also comes with loose rear end as well. Felt like I had soft sidewall rear tires. What I did with that same car that is safer was 15x7" rear with 195s and 15x8 front with 205s with the rear sway intact. That wider stronger tire in front made the car neutral and faster in corners. :thsumbsup:

Last edited by E90lova; 08-26-2015 at 10:16 AM.
Appreciate 0
      08-28-2015, 09:24 PM   #14
z3papa
Captain
United_States
90
Rep
752
Posts

Drives: 11 E92 M3 ZCP, 07 335i
Join Date: Oct 2009
Location: Bloomington IL

iTrader: (2)

I've run a car with no rear sway bar all the time, no sway for all but high transition courses, and a stock rear sway connected all the time. When I went without, I generally had between -3.5 to -4.0 front camber, and tuned in as much total grip up front, and then compensated my car's tendency to to snap oversteer by disconnecting the rear sway. That worked great for all but the most transition heavy courses (think West courses last several years) at which you could click off lost time as the year seemed to lag behind the front. When I had a half and and half setup, i.e. one where it would adapt to whatever type of course you had, it was a compromise as you were always shifting setup from non-transition to transition oriented setups and this was as I was implementing a custom Blanton diff. Finally, when I got it to the point where my diff was completely tuned along with suspension, the rear OE sway was reconnected but maximized grip in the rear to that of the front. Rule of thumb, don't dumb down one end to make up for excess grip on the good end of the car.
__________________
2011.5 E92 M3 ZCP.
Appreciate 0
      08-31-2015, 12:56 PM   #15
Kgolf31
Brigadier General
Kgolf31's Avatar
365
Rep
4,569
Posts

Drives: 2007 Z4MC, 2012 128i
Join Date: Sep 2008
Location: Ohio

iTrader: (4)

Quote:
Originally Posted by z3papa View Post
I've run a car with no rear sway bar all the time, no sway for all but high transition courses, and a stock rear sway connected all the time. When I went without, I generally had between -3.5 to -4.0 front camber, and tuned in as much total grip up front, and then compensated my car's tendency to to snap oversteer by disconnecting the rear sway. That worked great for all but the most transition heavy courses (think West courses last several years) at which you could click off lost time as the year seemed to lag behind the front. When I had a half and and half setup, i.e. one where it would adapt to whatever type of course you had, it was a compromise as you were always shifting setup from non-transition to transition oriented setups and this was as I was implementing a custom Blanton diff. Finally, when I got it to the point where my diff was completely tuned along with suspension, the rear OE sway was reconnected but maximized grip in the rear to that of the front. Rule of thumb, don't dumb down one end to make up for excess grip on the good end of the car.
I still think the rear suspension on these are are x100 better than the past E36 and like suspension.

I think disconnecting an rear OE swaybar is not a good thing.

Proven example, IMO

Appreciate 0
      08-31-2015, 01:30 PM   #16
Ginger_Extract
California-bound
Ginger_Extract's Avatar
United_States
267
Rep
1,360
Posts

Drives: BMW 135i
Join Date: Jan 2013
Location: Los Angeles, CA

iTrader: (3)

Wow, positive rear camber under load, guess that rear bar is doing something after all. A rear bar is still on my shopping list, to increase low speed rotation.
__________________
Streets of Willow: 1:27.7 CW 11/15/15; 1:29.5 CCW 8/15/15 |||| Autoclub Speedway ROVAL (CCW): 1.52.6 - 12/2/17
Willow Springs - Big Willow (CW): 1:35.8 - 3/31/18 |||| Buttonwillow #13 (CW): 1:59.3 1/27/18
https://www.facebook.com/JakeStumphRacing |||| http://www.youtube.com/user/RaceMeMZ3
Appreciate 0
      09-01-2015, 07:37 AM   #17
z3papa
Captain
United_States
90
Rep
752
Posts

Drives: 11 E92 M3 ZCP, 07 335i
Join Date: Oct 2009
Location: Bloomington IL

iTrader: (2)

Quote:
Originally Posted by Kgolf31 View Post
I still think the rear suspension on these are are x100 better than the past E36 and like suspension.

I think disconnecting an rear OE swaybar is not a good thing.

Proven example, IMO

After all was said and done, my preference was to have the bar attached but wanted to explain the process of arriving at that conclusion.
__________________
2011.5 E92 M3 ZCP.
Appreciate 0
      09-10-2015, 07:13 PM   #18
Taskmaster
Major General
Taskmaster's Avatar
Japan
2084
Rep
8,286
Posts

Drives: E92 LCI Msport 6 Speed
Join Date: Nov 2013
Location: Florida

iTrader: (5)

Quote:
Originally Posted by Kgolf31 View Post
I still think the rear suspension on these are are x100 better than the past E36 and like suspension.

I think disconnecting an rear OE swaybar is not a good thing.

Proven example, IMO

I have a crush on your car
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


All times are GMT -4. The time now is 02:36 PM.




1addicts
Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST