Maybe some pictures will make it clearer:

Strut Suspension

Unequal Length A-arm

The full writeup

Another good reference

 

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..

 

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...

 

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.