Sidestepping the matter of making it fit for a moment, it is possible to arrange a 3 link such that its side view swing arm (SVSA, or "what I assume you mean by "controlling arm") remains at least as long as the SVSA for a TA. That will define the same or a lower amount of pinion angle sweep as the TA, respectively. Basically what's required is a relatively longer UCA, more on the order of 65% - 70% of the LCA length (vs a little under 47% in the 2008 S197 or only a few % higher in the later cars). You'd almost certainly need to relocate more than just one UCA pivot point in order to also match the TA's AS% at rest, but this can be done.
Needless to say, I'm surprised that you can get results that good with UCA geometry changes that small.
How does the UCA AS% change with suspension movement with the above tweaks?
Regardless, though, unfortunately what we're talking about now is comparing a TA setup that exists today with a 3 link setup that
doesn't exist on our cars today.
3 link geometry will show greater variation in SVSA length than a TA at least for configurations with appreciable amounts of AS, but the AS% variability (plotted against ride height) for a 3 link is generally milder and can even be of significantly different shape within the range of possible suspension position.
I suppose that raises the question of when you might want to shape the AS% variability, and how you might want to shape it. I'd think you'd want the curve to be as flat as possible in order to maximize handling predictability.
For those more concerned with the actual location of the side view instant center (SVIC, aka IC to a drag racer), the 3-link is still significantly more variable and it may not be possible to match or better both the TA's AS% and pinion angle sweep over the entire range of ride height. The 3-link seems to get worse on the 'bump' or reduced ride height side of the static position in exchange for being better on the rebound side. Probably not what a drag racer or anyone who tends to drive like one would really want.
This implies that the TA tends to do better for those with relatively compliant suspensions as well, something that I suspected might be the case.
Getting a longer UCA to fit . . . you probably have to look outside the box a bit here, and while you're at it you can consider moving the UCA a little off center on the passenger side (there is a potential forward bite benefit in doing this - along with yet another potential trade-off).
This is essentially where the rubber meets the road. In essence, we're well past bolt-ons at this point.
AS% variability - advantage 3-link
Where you have full control over all aspects of the 3-link geometry, including link lengths, yes. But the
real question here is: what of the case where you're constrained to the S197's link lengths and, for the UCA, axle-side pickup point?
SVIC location stability - advantage TA
pinion angle sweep under acceleration (the more important side) - advantage TA
NVH vs most aftermarket UCAs - advantage TA
NVH vs proper bolting and more thoughtful UCA bushing design - I'm calling this one close enough to a wash
Do we have any examples of the bushing design you're thinking of here? No doubt it's a wash with proper bushing design, but the problem I see here is that the motion you wish to damp for NVH control is the very motion you wish to constrain as much as possible, and as a result you wind up with conflicting goals for the bushing.
Precisely why there are no absolutes in this stuff. There are always compromises.
Certainly. It always becomes a question of what compromises you're having to deal with, which is why you really
must define the goals
first -- so that you can fix the requirements, which define some of the compromises you'll have to make, before you start making decisions about approaches to take to solving the problems at hand.
Very true, though with stiffer springing PA sweep is going to be less than OE regardless of whether you swap in a TA or stick with any sane version of a 3 link.
True. And I wouldn't expect the spring rates would have to increase a whole lot in order to achieve that.
I probably don't rate NVH as high on the list of priorities as many, partly for reasons given previously, partly because I've always accepted more NVH as part of the price of performance, and partly because my hearing isn't what it used to be any more.
This is, I think, the central reason that so many here are reacting the way they are: their context largely discounts NVH. That's understandable given the OP's initial statement, which didn't include an important piece of context: the use of stock or near-stock spring rates.
It does (GM wasn't all that stupid for putting it on their 3rd & 4th gen F-body cars, which despite his current preference Sam Strano did have considerable success with). TA cars really are easy to drive.
There's value in that, too. Predictability inspires driver confidence, which enables them to push nearer the limits. You just don't want it inspiring
too much confidence.
The S197 probably wasn't designed for an optimized-for-track-day 3-link configuration either. I'd heard elsewhere that this was part of what got Griggs to do a TA for the S197 TA in the first place.
Yeah, I suspect the geometry (link length, especially) would be different if it had been.
A more track-oriented 3 link would likely be a more difficult installation than a TA even if all of the engineering, design, and fabrication was done by others and all you had to do was install it in the car. I would expect "some welding required".
Considering that you're talking about relocating the axle-side pickup point of the UCA, yeah, welding would almost certainly be required.
In any case, such a thing doesn't yet exist as a public offering for our cars that I know of, so we're left with the existing S197 geometry and the compromises it brings to the table.
Relative to
that, the torque arm seems to be a better overall solution if you don't mind the weight and don't have spring rates that would rattle your bones on the street, with its advantages being greater as the spring rates get smaller. Note that I'm not saying how
much better. With sufficient spring rates, its advantage will probably be marginal. On a car intended solely for the track, the only real advantages might be a bit of reduced variability in some of the parameters we've been discussing, if even that.
Just based on engineering considerations alone, if I had to choose between the stock 3-link geometry (even with the possibility of relocating one end of the control arms) and the torque arm
on a car with stock or near-stock spring rates, I'd almost certainly go with the torque arm. Indeed, it appears to provide more benefits relative to the 3-link setup on the S197 than does a watts link relative to a Panhard bar under those conditions.
Hence, the setup I'm considering, because NVH is a major concern for me, is one with near-stock springs (e.g., the Boss 302 springs or something similar), torque arm, a good adjustable panhard bar such as the Whiteline one, relocatable LCAs, and the best dampers I can lay my hands on.
Gotta give it up for the excellent icons on this forum.
