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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > RSB: 14mm vs 15mm vs 20mm



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      09-03-2010, 09:40 AM   #1
StealYourFace
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Question RSB: 14mm vs 15mm vs 20mm

I have a 2006 300i ZSP... The car has a 3.64 LSD rear.

I am retaining the stock springs, I have a set of the bmw perf shocks waiting to go on. At the same time I will also be doing M3 front control arms.

The final part of the equation is the rear anti roll bar. I don'ty know whether I should go with the 14mm m sport bar, the e93 15mm bar or the M3 20 mm.

I do auto cross, and am looking to help the car rotate even better.

I don't want the car to be nervouse on the street... I want to be able to let somebody use my car if its raining and not worry about the tail coming around on him

Lay it on me folks
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      09-03-2010, 06:42 PM   #2
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Quote:
Originally Posted by StealYourFace View Post
I have a 2006 300i ZSP... The car has a 3.64 LSD rear.

I am retaining the stock springs, I have a set of the bmw perf shocks waiting to go on. At the same time I will also be doing M3 front control arms.

The final part of the equation is the rear anti roll bar. I don'ty know whether I should go with the 14mm m sport bar, the e93 15mm bar or the M3 20 mm.

I do auto cross, and am looking to help the car rotate even better.

I don't want the car to be nervouse on the street... I want to be able to let somebody use my car if its raining and not worry about the tail coming around on him

Lay it on me folks
If you have the OE front bar, I'd stay with the 14 or 15. If you have a larger front bar, then you might try the M3 20mm bar. That's my $0.02.
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      09-03-2010, 11:59 PM   #3
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If you're autocrossing go with 20mm. Also take out the wheel/tire stagger. I've been saying that in a couple of threads now but it's really important. It'll still be fine on the street. If you're worried about other people just tell them to leave DSC on.

I have 245/255 front/rear tires and 15.8mm rear sway. It works great on the track but it would probably plow everywhere on an autocross.
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      09-05-2010, 07:34 AM   #4
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Rear sway is an expensive job. I would suggest springs for a number of reasons. If autocross is really a priority, I would give Hotchkis and also Harold @ HPAutocross a call to see what they recommend. IMO the 20mm rear anti-sway bar is not appropriate by itself for the 335, because it just amplifies the problems with the open differential. The 330 does not have the same level of torque, but you still are going to be unweighting the inside rear wheel.

Although I am a big fan of planning out an entire system and installing the whole thing one time (saving on labor and alignment in addition to having no weak links), in your case I suggest you try the M3 front control arms first, and some sticky tires. You can adjust under/oversteer balance with tire pressure, although that does not sound as sexy as a bigger rear sway.
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      09-05-2010, 08:37 AM   #5
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Quote:
Originally Posted by stressdoc View Post
Rear sway is an expensive job. I would suggest springs for a number of reasons. If autocross is really a priority, I would give Hotchkis and also Harold @ HPAutocross a call to see what they recommend. IMO the 20mm rear anti-sway bar is not appropriate by itself for the 335, because it just amplifies the problems with the open differential. The 330 does not have the same level of torque, but you still are going to be unweighting the inside rear wheel.

Although I am a big fan of planning out an entire system and installing the whole thing one time (saving on labor and alignment in addition to having no weak links), in your case I suggest you try the M3 front control arms first, and some sticky tires. You can adjust under/oversteer balance with tire pressure, although that does not sound as sexy as a bigger rear sway.
I am definately doing the M3 front control arms.

I won't change the springs because it snows here and I don't want the car any lower.. and I drive about 20,000 miles a year so comfort is more important to me that the 6 or 8 auto x events I do.

My car does not have an open differential, I have a 3.64 lsd rear in it.
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      09-08-2010, 12:28 PM   #6
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Bump, anyone more input?
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      09-08-2010, 01:28 PM   #7
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Bump, anyone more input?
The only way to know for sure, is test. Because swaybars are the least impactful variable in the equation plus how they affect handling depends heavily on a lot of other factors, I would get all three bars, test and see which one works the best and gives you the best time on the autocross course and which one is the most stable on daily street driving, then find the best compromise and sell the rest.

There is absolutely no way to even start to GUESS which bar would yield the best result. And there are a lot of other variables that you can adjust that will yield more grip elsewhere AND gives you the freedom to "rotate."

Lastly...This is why they make "adjustable" swaybars.
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      09-08-2010, 04:10 PM   #8
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The only way to know for sure, is test. Because swaybars are the least impactful variable in the equation plus how they affect handling depends heavily on a lot of other factors, I would get all three bars, test and see which one works the best and gives you the best time on the autocross course and which one is the most stable on daily street driving, then find the best compromise and sell the rest.

There is absolutely no way to even start to GUESS which bar would yield the best result. And there are a lot of other variables that you can adjust that will yield more grip elsewhere AND gives you the freedom to "rotate."

Lastly...This is why they make "adjustable" swaybars.

I couldn't agree more, you can't guess. I know some people have used the 14 as part of the same suspension that I am going with and was wondering if anyone else had experience with the 15 or 20.
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      09-08-2010, 05:39 PM   #9
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I couldn't agree more, you can't guess. I know some people have used the 14 as part of the same suspension that I am going with and was wondering if anyone else had experience with the 15 or 20.
While you COULD potentially take a pretty good educated guess based on someone else's set-up, there are too much variables to consider, especially when TIRE and tire pressure will play a bigger part as to how the car will react, plus you just can't trust anyone's knowledge level on most of these forums to even remotely be capable of assessing the balance of a vehicle anyway.

If I were you, and I am not so that accounts for Jack and sh*t...And Jack just left town. I'd get the shocks installed with the OEM rear bars, test and tune until you get the right tire size/pressure down along with the right alignment setting to get as neutral as you possibly can within the rules/hardware confinement, THEN if you still need more front end bite, think about the next size up sway bars. Otherwise all you're doing is chasing a wild goose.
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      09-08-2010, 09:20 PM   #10
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What about M3 subframe bushings
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