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

Bernie Benz b.m.benz at prodigy.net
Thu Feb 1 11:08:22 EST 2001

> From: "Smith, Kirby A" <kirby.a.smith at lmco.com>
> Date: Thu, 01 Feb 2001 10:45:53 -0500
> To: "'Bernie Benz'" <b.m.benz at prodigy.net>, C1J1Miller at aol.com
> Cc: 200q20V mailing list <200q20v at audifans.com>, audi-20v
> <audi20v at rennlist.org>, s-car-list at yahoogroups.com
> Subject: RE: [s-cars] Strut braces, here we go again!
> 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
> bushing.
> 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?
One is only halving strut top deflection with a perfect strut brace, not
removing it.  If you believe that deflections below the axle line are
relevent to this discussion, go research it and enlighten us.
> 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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