[200q20v] RE: [s-cars] Strut braces, here we go again!

Smith, Kirby A kirby.a.smith at lmco.com
Thu Feb 1 10:45:53 EST 2001

The tower-to-towe brace on my 90q made a (slightly) detectable improvement.
I can imagine tower archtectures such that even though they are made of
steel, will have a larger deflection at a given load than a hard rubber

If one removes strut top to strut top deflection with a strut brace as
described, reducing camber change due to bushing deflection, what about the
bushings locating the bottom of the strut.  I think one needs to know just
what is happening at each end before camber changes can be understood?

Kirby A. Smith   New Hampshire USA 
1988 90q Titanium gray, 192 kmi 
1988 90q Stone gray, 210 kmi 
1995 S6 Pearl effect, 92 kmi, A'pexi boost controller, Hoppen Stage 1 

> -----Original Message-----
> From:	Bernie Benz [SMTP:b.m.benz at prodigy.net]
> Sent:	Thursday, February 01, 2001 03:07
> To:	C1J1Miller at aol.com
> Cc:	200q20V mailing list; audi-20v; s-car-list at yahoogroups.com
> Subject:	[s-cars] Strut braces, here we go again!
> The ultimate goal any strut brace device is to minimize strut rod latteral
> movement relative to the ball joint, i.e. to minimize camber change caused
> by latteral cornering forces.  To understand the effectiveness of any such
> device, one must differentiate between a strut to strut brace and a tower
> to
> tower brace, and analyize how each differently affects strut rod latteral
> movement in a MacPherson strut suspension design.  The Benz Brace is a
> strut
> to strut brace, most others (all others, to my knowlege) are tower to
> tower
> braces.  
> The latteral cornering force exerted by the strut rod is first exerted on
> the compliant rubber bushing between the rod and the tower, causing
> deflection therein, and is then passed on from the bushing to the tower,
> causing tower deflection.  In the ultimate corner, this maximum latteral
> cornering force is transmitted only from the outside strut rod (inside
> wheel
> off the ground) to its rubber bushing, causing a maximum deflection of
> this
> bushing, and thereon to the outside tower, causing a maximum deflection of
> this outside tower.  Thus the total outer strut rod movement causing
> camber
> change is the sum of bushing and tower deflections.  Further, realize that
> stiffness of the welded steel tower is orders of magnitude greater than is
> the compliant rubber bushing, i.e. bushing deflection is much greater than
> tower deflection
> A tower to tower braced system divides the tower deflection between both
> towers but retains in full the larger deflection of the outside bushing,
> and
> thus results in only a small camber change improvement over the unbraced
> condition.  Further, because of the high stiffness and resultant small
> deflections of the towers, to be effective in dividing tower deflection
> forces between the two towers a tower to tower brace must be extreemly
> stiff.  None are, most having bolts, brackets, and bends.  IMO, they serve
> only as cosmetic window dressing and a lighter wallet.
> Contrast this with a strut to strut braced system, in which the brace
> divides the latteral cornering force equally between the two strut tower
> systems, bushings plus towers.  The resultant movement of the outside
> strut
> rod is half of the same unbraced system, and considerably better than the
> tower to tower braced system because, by design, the t to t has excluded
> bushing deflection, whereas the s to s has included bushing deflection in
> the dividing process.
> Think about it!
> Bernie.
> .     
> > From: C1J1Miller at aol.com
> > Date: Wed, 31 Jan 2001 14:39:44 EST
> > To: <b.m.benz at prodigy.net>
> > Cc: <200q20v at audifans.com>
> > Subject: Re: [200q20v] Re: Strut Brace
> > 
> > In a message dated Wed, 31 Jan 2001  2:15:46 PM Eastern Standard Time,
> Bernie
> > Benz <b.m.benz at prodigy.net> writes:
> > 
> > << Chris, from a strength of materials perspective a bent tube is
> useless as a
> > load bearing column, including all of the S4 stock and aftermarket tower
> to
> > tower braces.  Further, the brake fluid reservoir is not in the way of a
> > straight strut to strut brace.
> > 
> > Bernie
> > 
> >>> 
> > 
> > Nah, just make the walls of the tubing thick enough.  Again, deflection
> is
> > very small; forces are fairly small.  Without the brace, the car is
> _almost_
> > stiff enough.  You're not trying to withstand _all_ the forces, just add
> > strength to the existing structure.  Point taken, though; if the bar is
> bent,
> > you're using a spring to keep the struts apart...
> > 
> > Again, simplest (for a strut tower brace, not Bernie's style, but the
> S4/6 or
> > V8 style) would be to use Audi's parts, including the brake fluid
> reservoir.
> > Haven't tried to swap it, but expect it would be a swap...  Anyone have
> both
> > cars?
> > Chris
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