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-   -   Strut Question (http://forums.pelicanparts.com/porsche-911-technical-forum/192617-strut-question.html)

JSDSKI 11-16-2004 09:18 PM

Strut Question
 
Bilstein shocks are inverted inside the front strut, right?

Is this the major advantage for using a Bilstein strut versus a Boge with a Bilstein insert ?
Just what is the performance difference between the Bilstein strut and a Boge (or Koni) strut with a Bilstein insert?

Aside from the magic go fast green color, that is....

djmcmath 11-16-2004 10:10 PM

Well, the Bilstein name is worth quite a bit, at the track, I'm told. Just like flashing the Porsche key-fob earns you whole seconds off your lap times, almost effortlessly!

(ahem) The question is one of unsprung weight -- with the insert upside-down, most of the mass becomes sprung, instead, which reduces transition uncertainty and helps keep the wheels on the road (generally considered a "happy place" for most wheels).

That's simplistic. If you wanted a real performance measurement, you'd have to take apart the insert to determine how much each part weighed. If you didn't feel like dismantling an expensive car part, you could estimate that it's maybe 65% on the one chunk, and 35% on the other. Then you could make an estimate as to the total unsprung weight for that corner, and you'd have something to relate that number to.

(sigh) I'm sure I'm only partially right, and that I've simplified out a lot of important variables. With any luck, we'll be able to draw out the gurus of the board (you guys know who you are!) for a great discussion of suspension dynamics. :)

Dan

Chuck Moreland 11-16-2004 10:17 PM

Bilstein inserts for boge struts are also "upside down".

The unsprung part for the bilstein strut is lighter, it's just a shaft. The unpsrung part for boge is a hollow tube and a bit heavier. But the guts are still sprung.

Bilstein struts themselves are sturdier than the boge counterparts.

JSDSKI 11-17-2004 07:42 AM

Carbon fiber / kevlar key fob - really light and effortless - almost turns itself

Thanks, guys.

Wil Ferch 11-17-2004 09:10 AM

Chuck:
Are you sure?...I believe Bilstein INSERTS in Boge housings work the same way...and have the same orientation...as other brand inserts into Boge housings....

??????

Wil

Oldporsche 11-17-2004 09:29 AM

I always thought that there was a little more to the design. The Bilstein solved two problems. It turned unsprung weight into sprung weight and also captured any aireation of the shock fluid in the top of the shock. The valving being in the bottom of the containment area thus always worked with fluid and not foam.

David Duffield

JSDSKI 11-17-2004 11:18 AM

So far we have three listed advantages to the Bilstein design:
1) unsprung vs sprung weight (slight advantage)
2) sturdier strut (better control of mechanical forces ?)
3) reduced fluid aireation (better control of damping ?)

But - no adjustment (unlike some Koni's)

Anything else?

randywebb 11-17-2004 01:01 PM

Heft a wheel with a tire on it. Now heft a brake rotor. The diff. above is pretty small in comaparison. There is a comparative analysis of this with a pie chart in my Light Wt. Excel file on Thom's web site if you want a visual on this.

Of course, it does not hurt (well....except that the wt. is now higher rel. to the roll ctr.)

But the sprun/unsprung item is minor issue -- the rel adv.s are better control of wheel movement.

JWest 11-17-2004 01:29 PM

Chuck is correct, the Bilstein insert for a Boge strut has a very large diameter rod (containing the unsprung shock innards) extending to the upper mount.

The lower portion of the Bilstein for Boge LOOKS like a conventional strut insert, but is hollow and very light because it contains only the thin pistion rod interally.


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