aftermarket strut tower brace comment

[Tmoose]

I was reading the June 2013 Car and Driver at the dentist's office. On page 36 / "upfront - TECH DEPARTMENT" Don Sherman talks about "the lab test rig that tells you everything you'd ever need to know about a car's chassis." Next to last paragraph says "Simon adds that he's never seen an aftermarket strut tower brace provide a measureable handling benefit."

Since so many of them have hooks, kinks, jogs and bends I can easily believe that. Anything but a straight line relies on the bending stiffness of the strut cross section. And they tie strut to strut, so at most could double the stiffness, if the inner tower wasn't being asked to do anything else anyway.

http://www.challengertalk.com/forum...-vs-strut-brace-reality-strut_tower_brace.jpg

For sure the (factory) brace on 60s Mustangs did "something" as it was part of the Shelby set up that was a pretty effective race car in 1966 and 1967

http://www.ebay.com/bhp/mustang-export-brace

http://tuninghost.ro/wp-content/uploads/2010/01/021first66gt350bj.jpg

http://images.hemmings.com/wp-content/uploads//2012/11/ShelbytransAmmustang_03_2000.jpg

But that brace tied the shock towers not to each other, but into a portion of the firewall that was oriented parallel to the applied force, which satisfies the requirement for a successful load path as defined by the great Omer Blodgett.

http://modernsteel.com/Uploads/Issues/February_2013/022013_steelwise.pdf

" One must always provide a proper load path so the force can enter into the section that lies parallel "

Carroll Smith, Greenwood, Herb Adams and all the others make it pretty clear that most rubber bushings' compliance is often the primary "spring" in the deflection system anyhow.

 

[MikeHalloran]

Luckily for the strut-tower-brace business, the people who buy them don't care to know about any of that engineering type stuff.

... so the people who 'design' them have no need of real engineering skill, either.



An excellent discussion of related issues can be found in Phil Irving's "Motorcycle Engineering", where he talks about the evolution of the classic Greeves motorcycle's "frontbone".



Mike Halloran
Pembroke Pines, FL, USA

 

[cibachrome]

What I have done to answer the strut tower brace question is to intrument (by strain gauges) the braces themselves. Forget the handling measurements. Just put a meter up on the dash to show the forces carried by both parts. Then let the Chief and his crew go out and play car-car. If there is any maneuver or section of roadway that can produce more than a few lbs of force, then the cost might make for some discussion.

But it usually shuts them up permanently. Put the money into better tires, wider wheels, an improved steering valve or hydraulic bushings.

The machinery that you described is a kineatics and compliance machine (sold by MTS or Anthony Best for example). It usually can't find much of a difference either unless the unibody structure is seriously deficient. BTW: Make sure when you do the A vs. B comparison, you don't remove them. Only disconnect one end so that the change in figmosity doesn't affect (hurt) the feelings and sensations of a naive marketting type evealuator pressed into service for an Engineering ride. Make them evaluate it blind, too. (That means don't reveal what condition they are evaluating. Make them guess which one is which).

 

[GregLocock]

I worked on one small car where the spring towers moved inboard by 6mm each when you let the thing down off a 2 post hoist. I am fairly confident that that vehicle would have benefited from a strut brace.

Cheers

Greg Locock


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[RossABQ]

For sure the (factory) brace on 60s Mustangs did "something" as it was part of the Shelby set up that was a pretty effective race car in 1966 and 1967
....
But that brace tied the shock towers not to each other, but into a portion of the firewall that was oriented parallel to the applied force, which satisfies the requirement for a successful load path as defined by the great Omer Blodgett.

Interesting about that export brace, I know for sure that 6-cylinder Mavericks came with virtually the same thing, only (as I recall) in 2 pieces. What always astounded me about the Ford variants of the period was that there was nothing connecting the bottom side of the frame rails, like near the engine mounts. The radiator panel was flimsy sheet metal, so it didn't help.

 

[NormPeterson]

What Greg mentions supports the notion that the most likely performance improvement would be under severe braking where the two tower tops will be moving in opposite directions (rather than in the same direction by slightly different amounts as is the case while cornering). It would take at least a three-point strut tower tie bar configuration involving the firewall/cowl structure to add enough general torsional stiffness to even begin to matter as far as chassis torsion is concerned, and I'm sure that an X-braced four point arrangement attaching out near the A-pillars would be better still.

Buick installed two point strut tower braces as OE on at least some of their sedans only a few years back, but I doubt that its effects on either cornering performance or handling balance were considered as being much more than incidental to reductions in NVH and cowl shake . . . which also addresses quite nicely the anecdotal claims of "feels more solid" by those who have fitted STBs to cars that do not feature them as standard structural fitments. Even the much larger cross-section two point lower lateral tie that I added to a different chassis was more noticeable for the changes it made in NVH than in any easily recognized improvements in autocross performance.


Norm

 

[GregLocock]

While it is 'obvious' that a stiffer car will handle better, it is actually rather hard to measure. On the other hand if a particular mounting point is /severely/ deficient then rectifying that by bracing can make a measurable effect. Having said that, I am quite happy to go along with the subjectivist viewpoint that we can't actually measure every last detail of what makes the driver happy (yet) so there is still some wiggle rooom, and damper tuning in particular (and hence shock absorber mounting points) is still a bit of a black art. So while it may be hard to model an improvement in lap times from a stiffer shell, or a strut brace, I can quite believe that one way or another it helps. The benefits in shake,secondary ride, or structural feel, or whatever you like to call it are directly measurable.

My guess is that we'll need another factor of 2-4 in transducer density and modelling accuracy before we'll catch that sort of nuance in steering/handling.

If we go the other way and look at ladder frame pickup trucks, then the stiffness of the ladder frame is an integral part of the vehicle's handling, trying to get a good grip on modelling the truck for handling assuming a a rigid chassis is fraught with difficulty.



Cheers

Greg Locock


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