Rennline Strut Brace - DUAL 2-point vs 3-point

[Wickd89]

Hi Guys,
I need your help picking an upper strut tower. I have narrowed it down to two units from Rennline (great machining, light, solid, and they follow the Porsche factory connection points for the 3 point setup).

What should I get??
I like the "DUAL" 2Point system, but would consider the 3Point system if you guys think it is worth the extra space and effort.

Here is the link to the two options (DUAL 2-point vs. 3-point).

Please speak from experience.........
If you have either unit, it would be great to hear from you as well!


http://rennline.com/product.php/sid/5/aid/172/auto/Porsche/prodid/112

[Wil Ferch]

The dual two point still only reinforces the topside-plane... and does nothing to prevent a "rectangle" ( frontal elevation view) from becoming a parallel-o-gram. Only an added triangulated member can prevent this.

You need to decide how "good" you want to go. The top strut ( either single or dual mount) does some good...the triangulation goes further with the negative of more trunk space intrusion.

Don't forget...rubber is softer than steel ....and the top shock mounts are still encased in rubber ! do you want to go even further and add top mono-balls ??

See Chuck Moreland's Elephant Racing web site for details on this concept....with animated pictures.

- Wil

[Wickd89]

Speaking from an engineering standpoint, these combined components have 6 degrees of freedom (3 axis, x,y,z)

The regular bar - addresses only 1 axis.

Dual Bars -address 2 axises (but the second one is not as critical and "may not" be an issue)

The Triangle setup - addresses 2 axises (probably the two more important axises)

Hard to decide.....

[Wil Ferch]

Not too tough to decide...my "hint" was that the top rubber mounts will deflect way before the metal of the shock towers ever will.....

-Wil

[911pcars]

MHO. The early 911 chassis were not particularly rigid compared to the latest versions, even compared to some mundane late model sedans. Therefore, anything one can do to add rigidity to the basic structure is a plus for handling. Try this. Park the car so the front end straddles a steep driveway at an angle with the rear end on a relatively level surface (basically putting more load on one corner). See if the front doors open and close easily.

Here's our version of a triangulated strut bar using a single strut bar WM as a basis.



Sherwood
www.seinesystems.com

[Wil Ferch]

Sherwood:
I agree in principle.
Triangualtion is "better". I think I said the same thing. The question a user must ask is how much ( and where) of an improvement does he want or need..and then...will the best answer structurally fit the bill for street usefulness....like reduced trunk space. We also must bring up the relative usefulness of the various incremental steps we can take. As much as the towers gain strength is this arrangement ( and triangle is better than a simple cross-bar)...we can't overlook that the top rubber-encased shock mount will deflect under cornering load much before any of this stuff has an effect.

However I will admit that my own car with a triangulated system and rubber bushes....does indeed feel much different and stiffer during driving than before.

- Wil

[911pcars]

"However I will admit that my own car with a triangulated system and rubber bushes....does indeed feel much different and stiffer during driving than before.
"

Wil,
Mine too.

Sherwood

[Bill Verburg]

I would take my cue from what the factory did

[randywebb]

The car BIll posted appears to have rubber encased shock mounts, hence probably not coil-overs(?)

I think we need to distinguish the effects on rubber encased conventional suspensions vs. the all metal ones that some run on the track. The latter usually have coil-overs as some of the 'later' factory cars did.

[911pcars]

30+ gallon plastic tank?

Sherwood

[randywebb]

note the dual fuel pumps also...

but back to the strut...

[Bill Verburg]

that car is a factory RSR circa 1973, every factory installed brace since has been the same type, except the 934, which used an X to the front corners of the trunk.

[911pcars]

I have my doubts the existence or absence of compressible rubber strut bushings will mitigate the effects of a flexible chassis, otherwise, chassis rigidity isn't really a factor. But that isn't the case is it.

Sherwood

[randywebb]

I will let you and Wil argue that - there are two ways to do this:
1 - model it based on engineering (including a verbal model, if the difference in effects is so large that quantification is not needed), or
2- measure (including subjective driving comparisons)

I'm not sure when the factory switched to metal monoballs. I know the RS didn't have them, not sure about the '73 RSR, 3L RSR, or 934...

[Wickd89]

All great comments fellas!

Has anyone used Rennline tower braces??

[911pcars]

Originally posted by Wickd89
All great comments fellas!

Has anyone used Rennline tower braces??

I don't see any inherent drawbacks with most of the aftermarket strut bars besides cost, However, I prefer more than one mounting bolt to the chassis. The factory bar uses a weld-on bracket, two less things to potentially loosen, but welding isn't exactly DIY, something many owners prefer.

Sherwood

[spuggy]

Huh. I was just looking at the Ruf SC strut tower kit earlier today.

It looks very similar to the factory setup Bill shared, weld-in brackets and all:

http://www.rufautomobile.de/content.php?seite=shop/produkte.php&details=137

[Wickd89]

Nice brace but I was hoping to not weld or drill; since I an primarily a weekend canyon carver (at best).
thx...

[Dixie]

I have tracked my car with, and without, a strut bar. Personally, I think you can't tell a difference in rigidity. But then again, I'm not running monoballs.

So why did I buy a brace? So I could crank in some extra camber.

So why did I buy the dual setup? It was the same price as the single bar. I found out that the second bar actually makes it harder to crank the towers in.

[Wil Ferch]

Hey Rob:...cover that positive battey terminal !!! ...

- Wil