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      04-17-2014, 01:32 PM   #1
sBox
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Front/rear sway bar questions on stock M-Sport

So I have a 2012 128i M-Sportwith 4k miles. Don't need another ticket with a 135i. My driving record is longer than most newspaper's A section. Bought it from a dealer with 453m a month ago, I am the first owner and I have warranty . Love the balance, but hate the body roll. Now that that's out of the way...

I'm doing the suspension first, before tire/rim fitment. The car will be tracked 3-5 times a year, with the occasional autocross, but it is a daily driver. M-Sport stock springs/struts, etc.

I'm replacing the front control arm bushings and the rear subframe with PowerFlex ones. My question is with sway bars. I've read a lot of this forum including the TC Kline article. A lot of folks are upgrading the front but not the rear sway bar. Is there a reason not to upgrade the rear with an adjustable at the same time with a stock differential? What set did you choose?

Next, I'm expecting NVH but what are your experiences with additional noise and/or creaking with non-OEM bar(s)?
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      04-17-2014, 04:32 PM   #2
128Convertibleguy
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Quote:
Originally Posted by sBox View Post
So I have a 2012 128i M-Sportwith 4k miles. Don't need another ticket with a 135i. My driving record is longer than most newspaper's A section. Bought it from a dealer with 453m a month ago, I am the first owner and I have warranty . Love the balance, but hate the body roll. Now that that's out of the way...

I'm doing the suspension first, before tire/rim fitment. The car will be tracked 3-5 times a year, with the occasional autocross, but it is a daily driver. M-Sport stock springs/struts, etc.

I'm replacing the front control arm bushings and the rear subframe with PowerFlex ones. My question is with sway bars. I've read a lot of this forum including the TC Kline article. A lot of folks are upgrading the front but not the rear sway bar. Is there a reason not to upgrade the rear with an adjustable at the same time with a stock differential? What set did you choose?

Next, I'm expecting NVH but what are your experiences with additional noise and/or creaking with non-OEM bar(s)?
Sway bars are extremely tricky. The front and the rear do very different things, especially on a car with McPherson struts on the front. The front bar and the springs provide the vast majority of the roll control. The rear bar is largely for tuning the handling balance. It generally provides about 5% of the amount of roll control as the front, and only a couple of percent of the total roll control.

NVH is also tricky here. The contribution of the bar to those over two wheel bumps is minimal. One wheel bumps are another story.

People (not just BMW guys) muck about with sway bars a lot without understanding exactly what they do and how they do it. Not the best idea. That also means any advice you get here may be questionable. Including my post. <grin>

Bottom line. If you love the balance now, I'd be very wary of changing the rear bar.

Last edited by 128Convertibleguy; 04-17-2014 at 04:38 PM..
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      04-17-2014, 06:20 PM   #3
Kgolf31
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^ Basically summed it up.

BMWs are very weird. Typically if someone says, swap the front bar for a thicker one....People freak out and say you're going to cause more understeer.

BMWs will not do this (well, they will a bit).

A front bar will transfer weight to the rear wheels for traction. This helps power down. With added camber, you will not notice and negative effects...however, you may/may not experience some extra understeer. It is the nature of the game.

If you swap a rear bar, you're not essentially transferring that weight from the rear tires to the front. Now you're compromising rear traction and you'll probably have a bit more trouble putting power down. In addition, get on the power too early and you may see the rear end wave at you when you start spinning. A rear sway bar will make the rear end more loose and it will tend to want to come around.
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      04-18-2014, 10:22 AM   #4
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Years ago when I was modding my E46 a very knowledgable shop owner/auto tech/BMW guru advised that I put in a front sway bar but not a rear sway bar. I did as he advised and it was one of the best mods ever. The car really flattened out and understeer pretty much disappeared. Later on I added a rear sway bar because I found a used one for a good price. The ride quality really went down after that and I didn't even really feel a difference in the handling/body roll.
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      04-18-2014, 10:41 AM   #5
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My car as is dives far too much mid-corner and overwhelms the outside front tire, it needs to be flatter. Part of that is my fault running such a staggered setup for max rear grip (225/265). I’ll be doing the E93 M3 front sway and adding in a bit more camber (currently at -1.2 up front). Can you get to more like -1.5 with just M3 arms/tension rods? Maybe I’d need to add camber plates….The work never ends.
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