Advanced look at Strut Tower Braces

First and foremost, let me first say that i have an adjustable strut tower brace on my car. When i installed it the front end felt tighter, but SOTP meters are never right IMO.


Some points:
The front strut towers are made from very thick solid steel. Anyone ever notice when f-bodies wreck, no matter how hard they are hit, those towers will not give. I have seen that ring true many times.

I jacked the car up the other day from the side, in fact i had the entire passenger side in the air, while the drivers side was taking all the cars weight. I loosened the bolts on the one side of the STB, and marked the base off with marker. Then i let the car drop quickly down, and the STB and my lines didnt budge.

Has anyone performed skidpad test in the same conditions with and without the bar? Or a longshot, maybe put a spring scale between the towers and see if any force is applied?

I almost wonder if this mod that many advise, is all hype? The bar is also a PITA to work around too. Any real world views or test will be welcomed!

I think we're getting away from the guidelines for content on Advanced Tech, which is supposed to focus on engine and drive train. I guess we've already solved all those problems, and need to start looking at brakes and chassis...... :).

My first comment would be to call it what it is on the 4th Gens.... a shock tower brace, and not a strut tower brace. Then I would suggest that it be posted on the "Auto-X...." forum, because I think it has been discussed extensively there, particularly with regard to whether it provides any benefit. I recall a thread where they were regarded fairly negatively, for providing a more severe, less forgiving transition when the body was pushed to its limits..... but that's a vague recollection.

Fred-
Thanks for not moving this. You always seem to get much more responsive and helpful answers in here.

I searched over on the AutoX forum and only came up with one informative post, which was on 2pt vs 3pt braces. You dont happen to have a link do you?

Jared

I'm sure it was more than a year ago.... I think the complaint was that it made the chassis more susceptible to sudden breakaway on extreme cornering, and that some "flex" in the front end was better...... but I can't remember the details..... my car doesn't go around corners any more :).

I always felt the front end had a more solid feeling with the brace, but its hard to quantify, or prove. I was surprised how much the chassis flexed even with a roll bar, SFC's and my 3-point STB. I had the front wheels on ramps and jackstands under the rear subframes, and the car was level. It had been sitting that way for about 2 months, and I went to pull the pin out of the driver's side swign-out bar, and it wouldn't move. I eventually manage to pull the pin out, and then couldn't get it back in. I couldn't understand how the car, supported level on all 4 corners was flexing so much. When I went to pull it off the ramps, I realized the passenger side front tire was flat, and that misalignment was what had caused the chassis to flex so much. I put air in the tire, and the roll bar pin slipped smoothly back in......

Trying to keep this simple, roll bars help stiffen the chassis yes..Improve structual rigidy, no..The problem will lay in teh unit body assembly..Effective in its own right it proves to way ahead of the old well know ladder type frame..Ever see a hard launching G bdoy like a malibu with a stock frame cutting a 1.5 60ft..Pretty funny how the front clipp will twist and wiggle..I have actuall had a G body frame bare on it side and wobbled it like a piece of cardboard before i worked it..Here we move to the unit body..Industry terms it as a unit when refereing to it since it is made from many parts..To make it fast and cheaper to build its spot welded together..primraly made from thin ga steel that will flex on its own but together along with other parts does a fine job of holding the car together on the wheels..Add a roll bar that has been proerly installed you do make it stiffer but in between your attachment points of your downlegs and main hoop you still have that old somewhat flexy stamped steel.When i attach my main hoop i try my best to either tie into the rocker panel with the main hoop and door bars or at least install out riggers.Another problem that a unit body has is teh floor area is usually the weakest piont in the whole car.Roof panels and the rocker panels are not that strong and the firewall and rear shelf is called upon to box all this up..Not much when you think about it..Thats why you see many a new cnvertables with a hydroformed rail inside the rocker panels..Cryslers sebrings and the germans do this..(real fun cutting through it with a saw zall or chop saw:mad: :mad: :mad: )

Enter the strut tower brace..With front suspension affixed to the front crossmember and its job to support the engine its made from heavy thick material..But it cant lessen tornsional loads but itself to well, afterall its on the bottom only..Add the strut tower brace up top and then it gets help..This will make the car feel more stable over the road and the bumps and so forth that used to flex the hell out of the front of the car or back if you have one out back stronger..Think of it like boxed LCA's but in a larger form..The problem that really good drivers experence is that it then changes the dynamics of teh chassis, wich would require either a completely new suspension shock and spring settings to get the same reactions as before with better grip or one must relearn how to drive the car.

In my eyes most out there are a watse of money as they arent designed as they should be..To work best the would have to bewelded into the strut or shock towers anyways..GM H body FWDS have the best half assed ones ive seen..No sperical rods ends and the bar is boxed rail..Albiet small and bolted to teh struts.The adjustable units available to teh public do nothing more than preload the chassis in the worst way and still aloow the natural twisting to happen..

I always enjoy your chassis posts LT1 malibu. Stupid question, but which bar is the main hoop? Thanks!

No stupid question man, just people who dont know..:)

The main hoop is the bar that is right behind the seat and runs up the car to the roof and across..Its the starting point since the whole assembly gets welded to it.

Well since welding is better I just went out and welded mine on. :)

hmmm interesting information

This month's SAE mag has a small article on some Japanese-market Toyota wagon, and it comes stock with a strut-tower brace. Interestingly enough, it has a coil compression spring in the middle. The chassis engineer stated that under heavy cornering, it was transfering enough load to the opposite tower and deflecting both which made matters worse instead of better - so the compliance was added and handling improved. Since they still decided to keep the strut tower, it would seem that this means that you shouldn't be shooting for the extremes, but rather trying to find the balance between too much and too little compliance.

Seems like such a bar would be of very minimal use on a vehicle with twin control arms per corner, unless the control arm pivots had a load path into the shock tower.

Flybono, suspension settings..Not suspension components..If you stiffen up the chassis it will most likely react differently..Now im not super road racer but I can tell whats needed to be adjusted on a road race track..The street is way different and the irregular surfaces make it next to inpossible to get a good feel from the car..Make the frame stiffer wiether its in a good or bad way then it will feel worlds better on the street..I learned that years ago when i was slapping 1100 lbs coils under G body GMs.Sure did feel a lot better but the oversteer was unpridictable and down right scary...The last one i built pulled 1.1 Gs with autocross tires and 600lbs front coils..But still the frame was heavily modified to work better..

Thats an interesting find Eric..It seems to be true if you think about it..Unforqunatly aftermarket companys dont have that R&D avail to them..However I wonder how they determine how the springs compliance reacts to the unitbody flex...All teh while taking into account the requirements for NVH (noise vibration and harshness)..

Originally posted by atljar
I jacked the car up the other day from the side, in fact i had the entire passenger side in the air, while the drivers side was taking all the cars weight.

When you jack up the passenger side of the car, even when it's up all the way in the air, the weight of the car isn't all supported by the driver's side. I would tend to think all you high-tech guys would know such things. :rolleyes: pfff ;) :p :D

I'm bored and sick with a sore throat, so it's time for me to ramble on.

If you assume that the car is in static equilibrium, you can draw a simple 2-D free-body diagram of the jacked up car (with a view that looks towards the front of the car). With 4 forces: the weight of the car directed down through it's center of mass, the normal force due to the driver's side tire contacting the ground and it's friction force, and the normal force due to the jack under the passenger side.

If the normal force due to the jack is directed perpendicular to the car, that normal force will not be completely vertical, ie. it will be at an angle that is off of vertical as much as the car is off of horizontal.

Assuming the car is in static equilibrium, you can say the the sum of the forces in the y-direction sum to zero. From the FBD, you can see that the normal force due to the driver's side tire contacting the ground is = (the weight of the car) + (the normal force due to the jack)*(cosine of the car's angle).

So if you increase the angle the the car is at, for small angles you are only transferring some of the weight to the driver's side, not all of it. It's interesting to note that if you draw the normal force due to the jack completely vertical, the static equilibrium equations will say the the two normal forces are equal.

A lot of the over-simplified statics and dynamics anlaysis provide only a half-way accurate model of the real-world. Even the more advanced FEA analysis and other advanced computer models sometimes aren't all that accurate.

Arrrg, you made my brain hurt.

Well. All I know is, I installed my STB and big sway bays along with a PST front end kit 2 years ago. Everyone who drives my car says It handles corners way better than stock camaros.

Just curious, if the 4th gen is a "Macpherson SLA suspention".
That would Imply that the car uses macpherson struts. Now, they arent attached to the spindle like a standard macpherson suspension, but I think they should still be considered struts, not shocks. Mabye I'm wrong. Is there some sore of distinguishing charicteristic I do not know about?

Originally posted by Dave Feerst

Just curious, if the 4th gen is a "Macpherson SLA suspention".
That would Imply that the car uses macpherson struts. Now, they arent attached to the spindle like a standard macpherson suspension, but I think they should still be considered struts, not shocks. Mabye I'm wrong. Is there some sore of distinguishing charicteristic I do not know about?

The 4th Gen F-body is not a "Macpherson SLA suspention"... (nor "suspension" for that matter :D)... it is an unequal length a-arm (SLA) suspension. To me, the differentiator is the number of links in the suspension, and whether the shock also serves as one of the "links". The unequal length a-arm suspension is a "4-link" setup.... the chassis is one link, the upper a-arm the second, the steering knuckle the third and the lower a-arm the fourth link. The shock is not any part of the 4-link mechanism. It serves no structural function.

A MacPherson strut, on the other hand is (I guess you would call it??) a "3-link" setup, and since we all know 3 fixed-length links make a triangle, and can't move, we make one of the links variable in length. That is the function of the shock (aka "strut").... it is the sliding link in a 3-link mechanism. It has a structural function.

To me, that is the difference. The shock on the 4th Gen is "just along for the ride".... so to speak. It is not needed for any reason other than to dampen movement. The true strut on the 3rd Gen is part of the structure and the system can not function without it. It is more than a shock.

The part that seems to confuse people is the "coil-over" configuration of the shock and spring. Just because they are mounted concentricly does not make them a "strut".

huh, thats odd. I remember a few years ago my autoshop book had a picture of a "Macpherson SLA suspension" and it had an exact picture of the 4 gen F- bodies suspension. Mabye it was wrong.

Just acouple more ?s
If you did get rid of the shock you would also have no place to mount the spring. and the spring is neccessary for ride height. So how is that not a neccessary componet?

And how do the upper control arms count as a 4th link to the body. they are mounted the the chassis which is the 1st link to the body. Unless you are talking about the plates above the control arms (are those considered the shock mounts?) but even still. those are part of the chassis that is bolted to the body.

Maybe some pictures will make it clearer:

Strut Suspension (http://www.miracerros.com/mustang/t_animate_m.gif)

Unequal Length A-arm (http://www.miracerros.com/mustang/t_animate_a.gif)

The full writeup (http://www.miracerros.com/mustang/t_suspension.htm#Front%20Suspension)

Another good reference (http://autozine.kyul.net/technical_school/suspension/tech_suspension2.htm)

Originally posted by Injuneer
The 4th Gen F-body is not a "Macpherson SLA suspention"... (nor "suspension" for that matter :D)... it is an unequal length a-arm (SLA) suspension. To me, the differentiator is the number of links in the suspension, and whether the shock also serves as one of the "links". The unequal length a-arm suspension is a "4-link" setup.... the chassis is one link, the upper a-arm the second, the steering knuckle the third and the lower a-arm the fourth link. The shock is not any part of the 4-link mechanism. It serves no structural function.

A MacPherson strut, on the other hand is (I guess you would call it??) a "3-link" setup, and since we all know 3 fixed-length links make a triangle, and can't move, we make one of the links variable in length. That is the function of the shock (aka "strut").... it is the sliding link in a 3-link mechanism. It has a structural function.

To me, that is the difference. The shock on the 4th Gen is "just along for the ride".... so to speak. It is not needed for any reason other than to dampen movement. The true strut on the 3rd Gen is part of the structure and the system can not function without it. It is more than a shock.

The part that seems to confuse people is the "coil-over" configuration of the shock and spring. Just because they are mounted concentricly does not make them a "strut".

Fred, your graphics for the Mustang suspension were very good. The factual writeup was also quite useful. I'm not sure I agree with all of the author's conclusions as to what is "better" but that's just opinions.

I'm not sure if this is the place for some clarification of "number of links", etc. but here goes (with credit to Terry Satchell):

For any body(1) moving in space relative to another body(2) (wheel & tire =(1), chassis = (2)), body (1)'s motion can be described by 3 components of linear motion along 3 mutually perpendicular axes, (X,Y,Z). and rotation around those 3 axes. If X points forward, Y points right, and Z points down, rotation about X is ROLL, rotation about Y is PITCH and rotaton about Z is YAW. The point is we have 6 degrees of freedom; 3 translations along the 3 axes and 3 rotations about the axes.

To allow only the one path of motion of the wheel & tire which we want, we have to control 5 of the 6 degrees of freedom. Call the controls Degrees Of Restraint (D.O.R.). These D.O.R. are provided by the suspension links. All suspensions MUST have 5 D.O.R.

A single tension or compression link with attachments on either end is 1 link and provides 1 D.O.R. An A-arm, with three attachments is 2-links and provides 2 D.O.R. A MacPherson Strut is 2 links (2 D.O.R.). Think of the slider part as an A-arm of infinite length.

A SLA or double A-arm (aka double "wishbone") suspension has 2 A-arms of 2 links each (4) plus the tie rod (1) for 5 D.O.R. The MacPherson strut has 2 for the strut, 2 for the lower A-arm and 1 for the tie rod.

If the above is not totally confusing, you can see where the number of "links" come from.

The reasons designers choose any given suspension are many. Each has its advantages and disadvantages. The discussion of this would use a great deal of bandwidth.

As far as "strut tower braces" go, they can do some good if the car has a MacPherson strut suspension, especially if they are tied to the firewall where they become 2 links rather than one. Audi TT, a VW Golf IV platform has a 2-link strut tower brace, but the Golf and Beetle on the same platform don't. That's some of what the extra $ buys.

4th gen F's don't have strut suspension, as fred said, so the gains/losses from a 1-link brace are probably minimal, IMO.

FWIW, "MacPherson SLA suspension" is a contradiction of terms. It's either one or the other, not both.

My $.02

To keep is simple a strut is any damper that has an integral coil spring along with the upper mount that is the spring retainer and assembly mount in one..That comes from GM holander as well as the original technical writeups in the ASE updates bake in the early 80s when the tests were changed..

Macpherson is the term that has stuck with the design since it was named after the inventor..I beleave there is also a patent on the design but not quite sure..

Originally posted by LT1 1980 malibu
To keep is simple a strut is any damper that has an integral coil spring along with the upper mount that is the spring retainer and assembly mount in one..That comes from GM holander as well as the original technical writeups in the ASE updates bake in the early 80s when the tests were changed..

Macpherson is the term that has stuck with the design since it was named after the inventor..I beleave there is also a patent on the design but not quite sure..

To save any confusion...

There is a difference between a strut, as you described and a "MacPherson strut suspension". Here's a quote:

"The MacPherson strut suspension was invented in the 1940s by Earl S. MacPherson of Ford. It was introduced on the 1950 English Ford and has since become one of the dominating suspensions systems of the world because of its compactness and low cost.

Unlike other suspension designs, in MacPherson strut suspension, the telescopic shock absorber also serves as a link to control the position of the wheel. Therefore it (replaces) the upper control arm. Besides, since the strut is vertically positioned, the whole suspension is very compact. To front-wheel drive cars, whose engine and transmission are all located inside the front compartment, they need front suspensions which engage very little width of the car. Undoubtedly, MacPhersion strut suspension is the most suitable one.

Nevertheless, this simple design does not offer very good handling. Body roll and wheel's movement lead to variation in camber, although not as severe as swing axle suspension. From a designer's viewpoint, its relatively high overall height requires a higher hood and fender line, which is not very desirable to sports cars' styling."

Plain struts (shock and spring) like on the 4th gen F-body front don't take bending loads from location of the wheel. They are not providing any Degree Of Restraint, and are not MacPherson strut suspension components.

so.... to re-cap a macpherson strut is always a shock absorber mounted to the top of the spindle and the strut mount, If the spring is moved to control arm (like 3rd gens) it becomes a modified macpherson strut. If the strut is moved to the control arm and an upper control arm now connects the spindle to the sub-frame we call this A-arm/ wishbone/ ( in our case Short Long arm) I hope I got this right now...

Originally posted by Dave Feerst
so.... to re-cap a macpherson strut is always a shock absorber mounted to the top of the spindle and the strut mount, If the spring is moved to control arm (like 3rd gens) it becomes a modified macpherson strut. If the strut is moved to the control arm and an upper control arm now connects the spindle to the sub-frame we call this A-arm/ wishbone/ ( in our case Short Long arm) I hope I got this right now...

Sounds good to me.

It really doesn't matter what kind of spring is used or where it acts, unless, like some leaf spring suspensions, the spring is also a link.

In GM SLA front suspensions, some use coil acting on control arm, some use shock/coil (strut) acting on control arm, some use transverse composite leaf spring acting on control arm and some use a torsion bar acting on a control arm. All are SLA suspensions.

so I guess the conclusion is that STBs provide very minimal gains, if any, on fourth gen cars.