911 Front Strut Brace; Triangulated Better?

Hi everyone,

I am in search of a front strut tower brace for my 72 911T; and in my search, I have become curious about the engineering principles of triangulation.

I understand the principle to triangulation, now I want to know from knowledgeable 911 owners: "which is better as far as application, for the front end of my 911?"

Triangulated Front Strut Bar

or

Single Bar Type Strut Bar

Please give feedback...........


chris

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chris collier
collier@iglou.com

72 911T
(RS wannabe)

An interesting question that I would like answered also.

Does anyone know what the strut brace looked like on the factory RS rally cars cica '72-'73?

A couple of shops have recommended I buy a stut brace as I have an early car.
Both times the mechanic was not actually sales oriented their outfits did not sell braces, they had seen the benefits while aligning cars.

Both people seem to think a good solid brace going from tower to tower was enough (& worthwhile). The main problem being wing movement (inwards apparently) altering the alignment with time.

Basically their recommendation was for a simple brace to combat wing flex & accept that the alignment will change whilst conering due to movement in the upper thrust bearing etc.. Hence the more complicated braces were probably not worth the extra money.

I have since bought a simple Sparco brace that is basically a 1.5in. dia. Dural pole with adjustable eyes that mount to one of the upper thrust brng. bolts via a simple (strong) U bracket.

I think the cambermeister product is good but comes out at around twice the price by the time it's shipped to Europe and I'm not entirely sold on the bent brace.

But yes, both sources of advice said the majority of braces were trying to solve a problem that wasn't there.

My car is in bits at present, I'll let you know in a couple of weeks if the brace is worthwhile.

JG
'76 2.7S


[This message has been edited by Jon Green (edited 01-08-2001).]

Someone asked me to keep an eye out for aluminum tubing, next time I'm at Boeing Surplus. I'm still trying to make it ther, but will definitely look for the tubing.

This 'someone' suggests that a very adequate tower brace can be made for pennies, and I tend to agree. A track instructor told me that the tower brace has been one of the very most effective modification to his early SC tack car. go figure. I'll be looking for the tubing, to which ends can be welded.

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'83 SC

Would 'anyone' have a design that is proven to be effective?

I would be interested in what an adequate desined strut bar would look like.

I do have access to some very talented fabricators.

chris

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chris collier
collier@iglou.com

72 911T
(RS wannabe)

It's a really simple device. It just has, like, washers welded to the ends so it cann attach to the tops of the strut towers. It would be nice to also have a length adjustment so you can 'preload' the towers with tension. I don't have a specific design to look at, but 'someone' may have an idea, as this was his/her idea.

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'83 SC

If someone were to collaborate with me on a good solid design; I would be able to out-source the parts and have them manufactured for a very reasonable rate.

Anyone willing to help me with this, would of course be compensated in the form of parts.

chris

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chris collier
collier@iglou.com

72 911T
(RS wannabe)

I think I would want to use Chrome-Moly or Titanium tubing for the brace, and the large, 5/8" or 3/4" spherical rod ends won't be cheap, unless you can find surplus rod ends, too! Maybe Boeing pulls from the 737 rudder jackscrew recall????

I believe the factory bars are shown in Paul Frere's Porsche 911 Story. Or, maybe, Barth's Porsche Book.

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Warren Hall
1973 911S Targa

Does anyone have access to the exerpts from either of these two sources?

chris

I believe the factory bars are shown in Paul Frere's Porsche 911 Story. Or, maybe, Barth's Porsche Book.
[/B][/QUOTE]



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chris collier
collier@iglou.com

72 911T
(RS wannabe)

I'll look for the contact information for 'someone,' and get them into this loop. I'm in, too, because this thing won't weigh much and soem folks I know have sworn by them for handling reasons.

And with a large amount of respect, fully due, I'd say I think the jackscrew problem was with the MD-80, which is now being called the Boeing 717. I'm not sure they ever found the mysterious 737 tail ghost.

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'83 SC

Wasn't it the 737 that crashed outside of Pittsburgh? The best guess had something to do with sub-freezing temperatures and their effects on a hydraulic servo valve, as I remember.

Back to the topic, though, put me down for a grassroots-Pelican-board-designed-and-manufactured strut brace. I know there's a lot of debate about the effectiveness of these, but for a low enough cost, it seems like it couldn't do much harm.



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Jack Olsen
1973 911 T (3.6) sunroof coupe

I'm taking my 911 to a friend who can design and manufacture them. He used ot work with team Lotus and the Saturn teams also. I can get him to quote them in Qty. I believe the key is to hold the top of the strut still, preventing the rubber top bushing from flexing. Otherwise, go with spherical top plates ($$$$). Everone that is intersted, please email me with Qty and an acceptable price point. I'll coordinate and get back to each and every one.

PS. We're also going to look at heat exchangers, as I have a 3.2 and on the border of SSI pipe diameter, and I don't want to pay B&B prices.

email. Smatre@steeplechase.com

I'd like to see some collaboration between the great engineering minds on this board before we jump into manufacturing it. What are the problems with existing strut braces, and how can we make an improved one for pennies on the popular ones' dollar?

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Jack Olsen
1973 911 T (3.6) sunroof coupe

I agree that it is better to measure twice and cut once. In other words, let's "engineer" and challenge each other's ideas before we get a purchase together.

I am excited about the prospects, I just would like to have some good brain-storming before the fabrication gates open up.

chris

First thought:

Are we trying to keep the strut towers parrallel, allowing them the move; or are we hoping to eliminate pivot points in the bar, and hopefully decrease overall movement of the towers all together?

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chris collier
collier@iglou.com

72 911T
(RS wannabe)

I don't have the Frere book, I think it would save some development time to look at the factory brace.
They built the car in the first place!

Basically I'm sort of doing what you guy's are planning to do, I've bought a pre-fab brace bar though(for a ford or something) & making some brackets.

Luckily I have a friend who is a machinist at a local marine engineers, so bushes, fixings etc. are not a problem.

Not convinced that bracing the shock tops is the way to go. I'm sure it does move but the rubber top is there for a reason I'm sure. It would be easy for the factory to stiffen this up, so why haven't they? You have to consider the make up of the shock too.
It is simply a damper and not really designed to be used as a brace to preserve the steering geometry.

Basically I'm applying a bit of feedback from strut to strut by linking the camber adjustment bolts on the inside of the wing.
When one moves so does the other one.

The alignment shop agree too.
If it helps I'll produce some drawings of what I have done & post them up, it could be food for thought.

Being a engineer I am more than aware of the fine line between improvement & actually causing a different problem with your fix.

The brace I bought is tubular & quite beefy.
I really think the brace bar should be box section as the loading is compressional.

The mounting brackets I've seen, generally, seem to be too flimsy.

Can't wait to get my car back together & post some driving impressions.

JG

I mentioned bracing the strut tops becasue I read an interesting article in the Automotion catalog. Copied below

******************************************
The 911 is one of the most enduring designs in automotive history. Yet one design weakness has been discovered as tires have improved: the front suspension can lose its proper camber under hard cornering, reducing car control and cornering ability. Cambermeister solves this problem and provides advanced handling for your Porsche.

For years the myth prevailed that 911 front shock towers collapse inward under hard cornering. Many products flood the market based on this mistaken theory.


But the design people at Weltmeister did their own independent testing.


Using a precision tell-tale dial indicator that measures to within one-thousandth of an inch, they built a testing device to record shock tower movement under load. Tests at Laguna Seca, Sears Point and dozens of autocrosses revealed a surprise.


Shock towers do not collapse inward!


Rather, the shock towers spread apart under hard cornering. As you can see from the diagram, the cornering force from the tire's contact with the road, up through the strut, acts like a lever pulling the top of the struts apart. This forces the front suspension alignment to change to positive camber, reduces the tire contact patch, and causes a dramatic reduction in cornering ability.


Weltmeister's measurements showed that only 15% of the camber change could be attributed to shock tower movement. The other 85% took place in the rubber mounts for the top of the shock absorber!


To Weltmeister, the solution was apparent. First, the two shock towers must be firmly linked together. Second, the tops of the two shocks must also be tied into this structure. The Cambermeister design does it all--prevents shock tower separation or compression, as well as preventing 90% of the movement in the shock mounts.
*******************************************

It does make interesting reading, I saw this about a month ago which got me started on the whole strut brace thing.

I am sure the Weltmeister product is a very good emphirically engineered product.

The geometry changes under cornering are not quite as simple as the diagram suggests.
My colleages & I spent some time pondering this. And I have to be honest & say it's not too clear which effects are dominant or even important. The car chassis (body) flex is largely unknown.

I contacted two 911 alignment specialists & asked them 'after an alignment, 6 months later what's usually changed?'

I might get 2 sets of brackets made and weld one set to the dished washer on top of the shock & try the brace in different positions.

The factory brace placementis probably best. They have the best understanding of the system.

Although CAD simulation software exists today do not underestimate the engineering insight of 30 years ago.

I'll keep quiet now, promise.

Well, I'm not an engineer, but I'd like to stay in this game. It so happens I will visit Boeing Surplus tomorrow (with luck). This is not a reliable source of materials, but I may run into some tube titanium or something.

I agree that we should share information and consider the factory and Weltmeister designs. Measure twice, cut once. Talk this through.

I also understand that the strut tower tops move away from each other.

Perhaps the brace shoud hang onto the two fasteners on either side of the tower center, and shoudl also grab the center thing, only in a small rubber mount to allow some (but less than stock) freedom to this (center) thing. Can you tell I'm not an engineer? I bet not.

Just thought of something extra. Wayne's been pretty tolerant of us, but look where we're going now. We're building a parts co-op, perhaps even creating a vendor, or competitor. He'll lean over and tell Tom "The Board has decided to design and fab its own tower brace and they're talking about SSI knockoffs."

Not to worry, though. I don't think there's such a thing as an SSI that's not an SSI.
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'83 SC



[This message has been edited by Superman (edited 01-09-2001).]

I'm sure if it comes down to it, old_skul can host this BBS over at cheaterswayside.

My family's business (of which I am not a participant) is steel machining (specifically, electrical conduit fittings). I recall in the past having done some aluminum work as well. I'll see what kind of stuff we can do.

If the Weltmeister excerpt holds any truth (I haven't looked too deeply into it) then we're talking about the tensile strength of the "brace" bar. Any materials engineers out there who can give us a cost/benefit breakdown of steel/chrome moly/titanium/aluminum/other for tensile strength? What's the ratio of equal tensile strength for a steel/aluminum tube vs a titanium/chrome moly one? Titanium ain't cheap. Just look how many SR-71s the USAF could afford....

On that note we're also talking shear/torsional strength for the fittings to the actual towers. So I guess we have to look into that as well.

I haven't looked at either my shock towers or this Welt. product in the past so if I'm just blowing smoke please say so...

blue

Blue,

There is Titanium tubing suitable for bicycle frames, so it isn't that expensive, but I was specifically thinking of surplus, not retail prices! And, Titanium weighs about the same as Aluminum, and is almost as strong as steel ... the alloy variations don't really permit precise numbers.

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Warren Hall
1973 911S Targa

Heh...I thought about putting a "public" BBS up at the Gallery, but I rather enjoy using this version of the Universal Bulletin Board (UBB) that Wayne uses. (Actually, I don't know who his webmaster is.) And I don't want to take traffic away from Pelican; they do good business and have saved me a lot of cash, resulting in well over a thousand dollars worth of business from me alone.

But I don't think they'll care if we make our own shock tower braces. I'm patiently watching to see if someone offers one for sale for the so-called "pennies". I have some pennies, and no shock tower brace...

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Mark Szabo
1986 911 Targa 3.2
1987 Escort 5-speed 1.9
The Porsche Owners Gallery