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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Stock Anti-roll bar specs anyone?



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      03-07-2006, 07:58 PM   #1
ksfrogman
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Stock Anti-roll bar specs anyone?

I've searched the forum, but have come up short of finding the specs for the stock anti-roll bars on the e90.

Apparently Eibach and H&R offer anti-roll bars with different specs. Here are my questions:

1) Does anyone know what the diameters of the stock front and rear anti-roll bars are? If not, would someone with a micrometer mind measuring this?

2) Are the stock anti-roll bars solid or tubular (i.e., hollow)?

3) Most difficult question: Does anyone have the formula that shows the mathematical relationship between bar diameter and stiffness? If memory serves me right, a slight increase in diameter gives an exponential increase in stiffness.
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      03-07-2006, 08:11 PM   #2
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Well, I found something that essentially is something like this. Correct me if I am wrong.

Let Q = stiffness in lbs/inch
C = Constant
D = Roll bar diameter
L = Length of bar
A = Length of lever arm

Q = C * D^4/[L*A^2]

So stiffness is directly proportional to diameter ^4
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      03-07-2006, 08:11 PM   #3
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So far, this is what I dug up...
Front 26.5mm

Rear 13mm


I would guess the bars are hollow, but I don't know.

EDIT: Whoops, only the diagrams showed up...oh well, go to realoem and see for yourself...

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      03-07-2006, 08:24 PM   #4
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Thank you. This is real interesting. This is what MarkE90M3 posted for the aftermarket diameters:

Anti-roll bars:

Eibach: 28mm / 15mm (part # 2085.320)
H&R: 27mm / 20mm (part # 33211-1)
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      03-07-2006, 08:30 PM   #5
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Oh my! The H&R's will ROCK! The e90 must have a strong frame! With only a slight increase on the front, and a big one in the rear, the car will turn on a dime! Now I want a set of H&R's!

The Eibach's are sooo conservative, but that's whey we have a choice!

Danny

Quote:
Originally Posted by ksfrogman
Thank you. This is real interesting. This is what MarkE90M3 posted for the aftermarket diameters:

Anti-roll bars:

Eibach: 28mm / 15mm (part # 2085.320)
H&R: 27mm / 20mm (part # 33211-1)
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      03-07-2006, 08:37 PM   #6
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if I remember my schoolin correctly

stifness goes up to the to the third power as diameter of the bar changes

a small diameter change can be a HUGE stiffness change
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      03-07-2006, 08:40 PM   #7
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I just ordered a set of H&R Sport Springs along with the anti-roll bars. I plan to have them installed next Tuesday.

I didn't think I'd be "mod-ing" much of anything on this nice car, but here we go. I must control myself!
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      03-07-2006, 09:04 PM   #8
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Quote:
Originally Posted by ksfrogman
I just ordered a set of H&R Sport Springs along with the anti-roll bars. I plan to have them installed next Tuesday.

I didn't think I'd be "mod-ing" much of anything on this nice car, but here we go. I must control myself!
Why don't you compete the upgrade with some shocks? Seems logical to me!

Danny
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      03-08-2006, 12:37 AM   #9
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Quote:
Originally Posted by HRC
Why don't you compete the upgrade with some shocks? Seems logical to me!

Danny
This is a consideration. However, every car I added performance shocks to became very stiff riding. I'm not going for broke on the performance handling if it significantly compromises ride quality. I don't want my e90 to ride like a go-cart.
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      03-08-2006, 12:54 AM   #10
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Quote:
Originally Posted by ksfrogman
This is a consideration. However, every car I added performance shocks to became very stiff riding. I'm not going for broke on the performance handling if it significantly compromises ride quality. I don't want my e90 to ride like a go-cart.
get the adjustable shock. like koni. let me know if you want them i can get them for $590 from my friend. the install of course would be free. since you are installing your springs they can change them out for you. just give me a call....
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      03-08-2006, 12:59 AM   #11
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Quote:
Originally Posted by longtran
get the adjustable shock. like koni. let me know if you want them i can get them for $590 from my friend. the install of course would be free. since you are installing your springs they can change them out for you. just give me a call....
Yea, get Koni's! I've had the sports cranked out to max and all my cars felt good, a little stiff, but good (even on my preludes)! Turn them down to halfway and it's like riding stock, but better!

Danny
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      03-08-2006, 01:02 AM   #12
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Quote:
Originally Posted by longtran
get the adjustable shock. like koni. let me know if you want them i can get them for $590 from my friend. the install of course would be free. since you are installing your springs they can change them out for you. just give me a call....
What are you doing to me? I'm turning into a mod-man freakazoid.

Let me sleep on the idea of the shocks.
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      03-09-2006, 03:20 AM   #13
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How much are those Front/Rear anti-roll bars cost?

Thanks
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      03-09-2006, 05:48 AM   #14
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Quote:
Originally Posted by Thavee
How much are those Front/Rear anti-roll bars cost?

Thanks
$500 front+rear installed, but the install will be done the same time the springs are put in, otherwise i understand the labor cost would be more expensive.
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