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Old 10-28-2007, 09:04 PM   #1
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Sway-bar size...?

What's the size (thickness) of the stock front sway-bar on a '98 Box?

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Old 10-28-2007, 09:46 PM   #2
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I believe that S-spec RoW 030 front sway bar is 24mm thick,the Eibach is 24mm thick as well. Ordering the RoW 030 sway bar with bushings is a lot less then the Eibach,just something to consider. Now for the front your best bet is 2.5L/2.7L RoW 030 sway bar,the Eibach rear sway bar is the same as the S-spec,which is smaller then the 2.5L/2.7L RoW.


You may want to take a look at
http://www.cb-racing.com/boxster_030.html
http://cgi.ebay.com/ebaymotors/EIBACH-ANTI-ROLL-KIT-SWAY-BAR-PORSCHE-BOXSTER-97-03_W0QQcmdZViewItemQQcategoryZ33592QQihZ015QQitemZ 250152670518QQrdZ1QQsspagenameZWD1V
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Old 10-29-2007, 10:12 AM   #3
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Peer, from what I can determine and I am no expert at this is the front stock bar is 23.1mm and the rear is 18.5mm. I believe the '98 and my '02 still have the same size but more knowledgeable minds than mine can testify if this is true or not. Tomorrow afternoon I am having the S M030 front 24mm and rear 19.6mm base M030 installed. I will report back on the difference if detectable. I believe it will lean a little less not that it leans a lot now.

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Old 10-29-2007, 02:36 PM   #4
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Allen K. Littlefield wrote:
> Peer, from what I can determine and I am no expert at this is the
> front stock bar is 23.1mm and the rear is 18.5mm.

So the stock ones aren't that much thinner than the M030..?

> I will report back on the difference if detectable.
> I believe it will lean a little less not that it leans a lot now.

Yes, please do so -- I mounted some racing swaybars on my Eunos, which was one of the best upgrades I've ever done: http://ccrma.stanford.edu/~peer/roadster-swaybars.html

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Old 10-29-2007, 06:03 PM   #5
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Peer, from what I am told that much larger bars will make a difference. Some have posted the difference is remarkable. I will let you know what they do for me.

AKL
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Old 10-29-2007, 07:18 PM   #6
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Stiffness goes with the 4th power of radius. In other words, a little larger diameter makes a very large difference in roll stiffness.
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Old 10-30-2007, 12:34 PM   #7
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Quote:
Originally Posted by blue2000s
Stiffness goes with the 4th power of radius. In other words, a little larger diameter makes a very large difference in roll stiffness.

Lord have mercy, what a difference. I took a dogleg left and right turn at 60 on the way home from having the M030 bars installed and that little sucker din NOT lean at all. For the cost from Sunset out in Oregon, $235.00 including shipping for both bars and $170.00 installation, I would say that this is the most bang for your buck handling wise. I kept my 17" wheels and stock strut/spring set up and you can really feel the difference. Highly recommended if you like fast corners. What a difference a mm makes.
Down side is I found I really need a set of rear tires and I had not provided for that in the budget so some adjustments have to be made financial wise.

AKL
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Old 10-31-2007, 06:24 AM   #8
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Remember that while the M030 "S" bar is 24mm, it's also hollow. The 24mm Eibach bar is SOLID! Big difference in stiffness.

Front bars:
986 non-s standard suspension 23.1mm diameter 3.4mm wall thickness
986 non-s M030 suspension 23.6mm diameter 3.5mm wall thickness
986 S standard suspension 23.6mm diameter 3.5mm wall thickness
986 S M030 suspension 24.0mm diameter 3.8mm wall thickness
996 GT3 Bar 26.7mm diameter hollow
Eibach bar 24mm solid

Rear bars:

986 non-s standard suspension 18.5mm diameter 2.5mm wall thickness
986 non-s M030 suspension 19.6mm diameter 2.5mm wall thickness
986 S standard suspension 18.5mm diameter 2.6mm wall thickness
986 S M030 suspension 19.0mm diameter 2.7mm wall thickness

Yes the non-S M030 rear bar is the stiffest.
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Old 10-31-2007, 04:27 PM   #9
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Quote:
Originally Posted by John V
Remember that while the M030 "S" bar is 24mm, it's also hollow. The 24mm Eibach bar is SOLID! Big difference in stiffness.

Front bars:
986 non-s standard suspension 23.1mm diameter 3.4mm wall thickness
986 non-s M030 suspension 23.6mm diameter 3.5mm wall thickness
986 S standard suspension 23.6mm diameter 3.5mm wall thickness
986 S M030 suspension 24.0mm diameter 3.8mm wall thickness
996 GT3 Bar 26.7mm diameter hollow
Eibach bar 24mm solid

Rear bars:

986 non-s standard suspension 18.5mm diameter 2.5mm wall thickness
986 non-s M030 suspension 19.6mm diameter 2.5mm wall thickness
986 S standard suspension 18.5mm diameter 2.6mm wall thickness
986 S M030 suspension 19.0mm diameter 2.7mm wall thickness

Yes the non-S M030 rear bar is the stiffest.
The solid bar will deflect about 28% less for a given torque than the hollow one. But I wonder if you'd notice that difference if the car is barely leaning with the hollow bar.

So the solid bar would be a 1.549 on this chart:

http://www.cb-racing.com/boxster_030.html
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Old 11-01-2007, 04:33 AM   #10
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So slightly less stiff than the GT3 bar on full soft. Interesting.
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Old 11-01-2007, 05:27 AM   #11
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Quote:
Originally Posted by John V
So slightly less stiff than the GT3 bar on full soft. Interesting.
I don't know the thickness of the GT3 bar, but about 75% of the stress on a torsion bar is taken by the outer 25% of the radius, so the OD has a much larger influence on stiffness than if it's solid or hollow. So it makes sense that the GT3 bar, being so large in diameter, would still have a higher stiffness.
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Old 11-01-2007, 06:39 AM   #12
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The effective diameter of a tubular bar is calculated by raising the inner diameter and the outer diameter to the fourth power, then taking the fourth root of the difference between those two numbers.

The GT3 bar (26.7mm and 3.5mm wall thickness) on full soft is 67% stiffer than the standard 23.1mm bar. The 24mm solid bar should be 55% stiffer than the same bar.

Granted this assumes the 24mm solid Eibach bar has the same lever arms as the stock bars and this calculation neglects the bending effect of the lever arms, which could be significant with a tubular bar. The GT3 bar is bent differently than the stock bar (which is what allows it to be adjustable) but it does have the same length lever arms.


Last edited by John V; 11-01-2007 at 06:42 AM.
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