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Discussion Starter #1 (Edited)
As I had mentioned in the Master List of changes (differences) for 2015 SS there are significant differences in the rear stabilizer configuration between model years.

This includes different lower control arms, in addition to the bar itself, in order to provide the reinforced hole in the control arm for the bar link attachment.

Note in the parts illustrations (attached below) for the 2 bar configurations where there is an arrow and notation to show the difference in the reinforcement plate size--the 2015 version of the reinforcement is smaller to allow the stabilizer link to extend into the channel of the arm. The photos show the reduced size of the reinforcement and the hole for the link to mount.

It is easy to see the difference in bar design between 2014 & 2015. I do not presume this is anything directly related to F55, as the parts book only calls out FE3 as the common "must have". In other words, if someone is thinking of converting to 2015 spec on a 2014 SS, or even a Caprice PPV or G8, it may be a matter of just identifying the correct mix of parts, and bolt it on.

Here are the 2015 PN's (some may be preliminary, not all price currently:

1) 92294343 Shaft, rear stabilizer (no price)
1) 22786267 Clamp (L)
1) 22831250 Clamp (R)
2) 20942228 Insulator
2) 22761221 Link (kit)

As mentioned above, the lower control arms are specific to the stabilizer configuration, or at least a matter of keeping parts proliferation from creating assembly line issues.

The rear LCA's required (common with 2015 PPV):
1) 92457895 (L)
1) 92457894 (R)

Even though LCA's are common between 2015 SS & 2015 WN, the Caprice (PPV) uses the same rear bar for both 2014 & 2015--similar to 2014 SS, but smaller (20mm vs 28mm). The 20mm bar actually was first used on the production G8 GXP.

There is research to be done here, but I'm basing my initial thoughts on the fact that the aftermarket suppliers of replacements for these parts lump all Zeta (including G8 & Camaro) into a single PN that fits all variants--not to suggest that use of aftermarket LCA's would allow fitting the 2015 SS bar on a 2014 SS, or any G8, or PPV.

Case in point: BMR specifies the same part (TCA028) for G8, Camaro, and SS sedan, all years. Without seeing the part, it is not confirmed that the BMR arms work with the 1LE (direct-acting) rear bar. I do not know what could be radically different in the various GM control arms to prevent use across different models, as dimensions appear to be the same.

The 3 photos below show the current Camaro rear LCA, with the provision for the 2015 style bar. These are offered as a kit (2 arms), which are not side-specific, under PN 23484878--the individual PN is 20942237. If these will work in place of the 2015 LCA's listed above, the cost difference is significant, and will make the mod a more pleasant experience, financially.

The PN's provided were what was available at the time of my research, and are subject to change--if anyone pursues this, please re-verify the information. If I become aware of PN changes, I will update this thread.

I caution anyone evaluating this as a potential mod to your 2014 SS, that nothing has been verified as to fit/form/function, so unless or until someone does, I make no claims that this will work/fit, nor do I claim it will be an improvement of any sort.

Regardless of the relationship of this change to MRC (RPO F55), the theory of the new stabilizer configuration is that it is a direct-acting design. To me, this means it can reduce possible harshness in suspension reaction that may come with the narrower bar design (2014), and as stated in the original thread, the bar diameter may not need to be as large, for reduced mass.

There have been issues with the earlier (narrow) bar setup and links pulling apart--whether it was link failure or the attachment point for the bar on the LCA, or possibly both, I am not certain. The G8 community dealt with this, and the aftermarket recognized that the bar link attachment point was susceptible to failure--BMR, for example, makes a reinforcement kit (for VE - ie. G8--not sure about 2010/2011 Camaro) to address this, but, to be clear, the reinforcement kit is not applicable to VF, as the sway bar link on 2014 SS is different, even from early Gen5 Camaro.

The final interesting note is found in the Chevrolet Performance Parts Catalog, when you look at the 1LE suspension kit (springs, shocks, and bars--rear similar to 2015 SS):

The V6 1LE suspension kit requires use of SS brake kit (from PP book) for proper rear stabilizer bar clearance.

This note/concern may or may not be applicable to a 2014 SS, or earlier PPV, G8 GT or GXP, as the Camaro V6 does use different/smaller rear brakes than any of the VE/VF or WM/WN platforms. It's another validation point to be checked in the modification process--no idea what creates interference with the smaller brakes, and even though the 1LE kit is Camaro-specific, I would suspect the potential for a fit/clear issue might also apply to the sedans.

Comments/feedback welcome!
 

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It appears the factory 2014 SS LCA could be modified to the later design by notching the reinforcement plate and adding a weld washer for the new end link design. I am curious how the new design compares to the older one since direct-acting is better than having ratio.
Good research, Bill!
 

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Discussion Starter #4 (Edited)
Makss, if the Service Arm kit will work, from the standpoint of R&R time, and that they're already in the proper configuration, I'd save the OE arms for spares (or return to stock 2014 spec), but I understand that some would rather do it themselves--not out of the question, I will concede.

(from 2015 Chevrolet Performance Parts Catalog)
23484878 NEW!
1LE & Z/28 Service Modification Kit
(2010-2011 model years only)*

This kit includes the rear lower control arms and hardware necessary to properly install the stabilizer bars included in the 1LE and Z/28 suspensions.

(I don't quite grasp what this means)
This kit is needed for 2010 and 2011 model year Camaros only, as the size of the stabilizer bar clamp stud changed starting in 2012 for both the front and the rear bar clamps.

My take is (if these arms will work) that it does not rule out possible use on 2014 SS or other platform variants to permit installation of 2015 SS rear bar on an earlier model year sedan.
 

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I don't know what they mean by "bar stud clamp," but I assume they mean "end link." But, it does show pn#23484878 is MSRP of $75.00. No point modifying the old LCAs at that price.
 

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The 2014 SS rear bar attaches the same as the early 2012, not on the outboard pad



Here's a 2014 SS .... ignore the big shiny things



Moving the bar further out would result in more force applied to the LCA, so they could reduce the size of the bar. Still, I believe the 1LE has a 26 or 27mm bar... correct?
 

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Discussion Starter #8 (Edited)
Rear on 1LE is 28mm solid--fairly substantial, when considering the 2014 SS sedan has a 28mm tubular bar, albeit with a different shape, so generated force numbers could be much the same.

One difference is the 2014 SS bar has shorter "arms" than 1LE or 2015 SS. Your statement is accurate, but look at it this way--for a given bar size, one that is direct acting will provide greater resistance than one that is at half the distance to the pivot point of the suspension member.

Conversely, to achieve the same force (roll resistance) of the 2014 bar with the 2015 direct-acting design, the bar diameter SHOULD be less--but it still depends on the 2015 bar "arm" design vs 2014. Suspension motion inputs over the longer length of the 2015 bar, to my way of thinking, will be less harsh in the loading > unloading (dynamic) mode (if I'm making sense).

The real question is what is the diameter and working length of the 2015 "arm(s)" compared to 2014. The center portion of the bar (between the cradle clamps) is basically inert to the calculation, other than it's diameter and whether it is solid or hollow.
 

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I am curious how the new design compares to the older one since direct-acting is better than having ratio.
I wouldn't make that assumption. I don't think many purpose-built race car these days use anything close to direct-acting swaybars. I'm honestly not sure the tradeoffs, or why GM would change the swaybar configuration this much. I wonder if it's just a matter of getting things common between the Camaro and sedan platforms for cost savings?

It's been my expectation that MR dampers should allow them to stiffen the rear roll resistance a little on the car, so it can be more neutral in steady-state cornering for more grip and responsiveness. Those dampers can then alter the damper rate bias toward the front during transitions to keep the car stable. Without measuring both swaybars, we don't know if that's actually been done for the 2015.
 

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I wouldn't make that assumption. I don't think many purpose-built race car these days use anything close to direct-acting swaybars. I'm honestly not sure the tradeoffs, or why GM would change the swaybar configuration this much. I wonder if it's just a matter of getting things common between the Camaro and sedan platforms for cost savings?

It's been my expectation that MR dampers should allow them to stiffen the rear roll resistance a little on the car, so it can be more neutral in steady-state cornering for more grip and responsiveness. Those dampers can then alter the damper rate bias toward the front during transitions to keep the car stable. Without measuring both swaybars, we don't know if that's actually been done for the 2015.
Understood. My thought is that direct acting should be less harsh with less actual bar needed. -Very similar to shocks/springs with better motion ratio having less valving and lower spring rates.
You are on the right track thinking 'IF' the MR is indeed being used to control roll. It's very capable, but I wonder if our USA version will enjoy what the HSV engineers designed previously? If so, the '15 rear bar most-likely not work in a converted '14. -BUT, too many unknowns at this point.
 

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I ordered the BMR lower control arms TCA028 and found out that the factory sway bar end links are not compatible on these control arms. You will need to purchase BMR Sway Bar End Links ELK006.
 

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Discussion Starter #12
If so, the '15 rear bar most-likely not work in a converted '14. -BUT, too many unknowns at this point.
All the assumptions about interaction with MRC aside, why wouldn't the '15 bar setup work? The production '14 bar is 28mm, compared to 26mm front.

It may be necessary to consider '15 rear springs to soften the spring rate if the (rear) bar rate is higher. Valving may not be perfect....as you say, too many unknowns at present.
 

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All the assumptions about interaction with MRC aside, why wouldn't the '15 bar setup work? The production '14 bar is 28mm, compared to 26mm front.

It may be necessary to consider '15 rear springs to soften the spring rate if the (rear) bar rate is higher. Valving may not be perfect....as you say, too many unknowns at present.
Lots of unknowns on this one. My idea is this: IF the '15 bar is tuned to a chassis that is using MRC to share the roll control duty, then it might be too soft for a non-MRC '14 car. That is a big 'maybe.' The '14 bar has a different effective arm length and is mounted fairly close to the LCA pivot point. This means the '14 bar is designed to work against a ratio (ie, stiffer bar.) The new '15 design was most-likely designed to be more compliant due to its outboard mounting location and planned use of MRC. It will bolt into a '14 with no issues, but will it be effective enough?
 

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Discussion Starter #14 (Edited)
I really think too much is being made out of the MRC/rear bar relationship.

All high-performance variants of Camaro have the same direct-acting type of rear bar used on 2015 SS:

1LE - standard SS springs, 28mm solid rear bar, 1LE-specific conventional shocks

ZL1 - springs unknown, MRC shocks, bar size not confirmed

Z/28 - stiffer springs, smaller bar(s) compared to 1LE, Multimatic adjustable shocks


It makes sense (to me) that IF, as has been mentioned, the MRC system (in case of SS Sedan) utilizes "softer" springs to provide a more compliant ride in the softest setting of the MRC, the change to a direct-acting rear bar would be desirable to aid in maintaining that level of compliance, while at the same time providing F/R balance & roll resistance similar to what the 2014 rear bar provided with stiffer (rear) springs--without the harsher reaction to suspension motion inputs when using the 2014 bar.

The question then becomes just how much difference there is between 2014 & 2015 rear springs. It is a fair question to contemplate whether the 2014 rear springs and 2015 rear bar would shift the F/R balance to a point that the car would become unstable toward oversteer--loose or tail-happy.
 

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As I had mentioned in the Master List of changes (differences) for 2015 SS there are significant differences in the rear stabilizer configuration between model years.

This includes different lower control arms, in addition to the bar itself, in order to provide the reinforced hole in the control arm for the bar link attachment.

Note in the parts illustrations (attached below) for the 2 bar configurations where there is an arrow and notation to show the difference in the reinforcement plate size--the 2015 version of the reinforcement is smaller to allow the stabilizer link to extend into the channel of the arm. The photos show the reduced size of the reinforcement and the hole for the link to mount.

It is easy to see the difference in bar design between 2014 & 2015. I do not presume this is anything directly related to F55, as the parts book only calls out FE3 as the common "must have". In other words, if someone is thinking of converting to 2015 spec on a 2014 SS, or even a Caprice PPV or G8, it may be a matter of just identifying the correct mix of parts, and bolt it on.

Here are the 2015 PN's (some may be preliminary, not all price currently:

1) 92294343 Shaft, rear stabilizer (no price)
1) 22786267 Clamp (L)
1) 22831250 Clamp (R)
2) 20942228 Insulator
2) 22761221 Link (kit)

As mentioned above, the lower control arms are specific to the stabilizer configuration, or at least a matter of keeping parts proliferation from creating assembly line issues.

The rear LCA's required (common with 2015 PPV):
1) 92457895 (L)
1) 92457894 (R)

Even though LCA's are common between 2015 SS & 2015 WN, the Caprice (PPV) uses the same rear bar for both 2014 & 2015--similar to 2014 SS, but smaller (20mm vs 28mm). The 20mm bar actually was first used on the production G8 GXP.

There is research to be done here, but I'm basing my initial thoughts on the fact that the aftermarket suppliers of replacements for these parts lump all Zeta (including G8 & Camaro) into a single PN that fits all variants--not to suggest that use of aftermarket LCA's would allow fitting the 2015 SS bar on a 2014 SS, or any G8, or PPV.

Case in point: BMR specifies the same part (TCA028) for G8, Camaro, and SS sedan, all years. Without seeing the part, it is not confirmed that the BMR arms work with the 1LE (direct-acting) rear bar. I do not know what could be radically different in the various GM control arms to prevent use across different models, as dimensions appear to be the same.

The 3 photos below show the current Camaro rear LCA, with the provision for the 2015 style bar. These are offered as a kit (2 arms), which are not side-specific, under PN 23484878--the individual PN is 20942237. If these will work in place of the 2015 LCA's listed above, the cost difference is significant, and will make the mod a more pleasant experience, financially.

The PN's provided were what was available at the time of my research, and are subject to change--if anyone pursues this, please re-verify the information. If I become aware of PN changes, I will update this thread.

I caution anyone evaluating this as a potential mod to your 2014 SS, that nothing has been verified as to fit/form/function, so unless or until someone does, I make no claims that this will work/fit, nor do I claim it will be an improvement of any sort.

Regardless of the relationship of this change to MRC (RPO F55), the theory of the new stabilizer configuration is that it is a direct-acting design. To me, this means it can reduce possible harshness in suspension reaction that may come with the narrower bar design (2014), and as stated in the original thread, the bar diameter may not need to be as large, for reduced mass.

There have been issues with the earlier (narrow) bar setup and links pulling apart--whether it was link failure or the attachment point for the bar on the LCA, or possibly both, I am not certain. The G8 community dealt with this, and the aftermarket recognized that the bar link attachment point was susceptible to failure--BMR, for example, makes a reinforcement kit (for VE - ie. G8--not sure about 2010/2011 Camaro) to address this, but, to be clear, the reinforcement kit is not applicable to VF, as the sway bar link on 2014 SS is different, even from early Gen5 Camaro.

The final interesting note is found in the Chevrolet Performance Parts Catalog, when you look at the 1LE suspension kit (springs, shocks, and bars--rear similar to 2015 SS):

The V6 1LE suspension kit requires use of SS brake kit (from PP book) for proper rear stabilizer bar clearance.

This note/concern may or may not be applicable to a 2014 SS, or earlier PPV, G8 GT or GXP, as the Camaro V6 does use different/smaller rear brakes than any of the VE/VF or WM/WN platforms. It's another validation point to be checked in the modification process--no idea what creates interference with the smaller brakes, and even though the 1LE kit is Camaro-specific, I would suspect the potential for a fit/clear issue might also apply to the sedans.

Comments/feedback welcome!

...................................
 

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Discussion Starter #17
Glen, if you look at Post #1 in the thread, you can see the link configuration for the 2014 SS (first illustration). The lower (on control arm end) link joint is revised to be a double-shear design, and the LCA link attachment has been rotated 90 degrees.

The BMR LCA's are designed for the configuration found on earlier VE/WM LCA's. The use of the BMR adjustable link provides the ability to connect the rear bar (even if stock) to the BMR LCA's--at the mid-point of the LCA.
 

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Discussion Starter #18
VF platform & sway bar design evolution

Posted Dec 31 2013 <<click to view - some here may not have seen this. The article (linked below) only offers some specifics, so some things, as we've been discussing the sway bar, for example, may be based more on assumptions, hunches, or past experience/observation, even in other vehicles. At the point of the transition to VF, the direct-acting (DA) rear sway bar was found only on the Camaro in the Zeta family. That it has now been adopted for this particular VF application is something we've been speculating about.

My theory is that the chassis re-tune and mass reduction implemented in VF permitted/included an overall reduction in spring RATES relative to VE. As mentioned in the bullet-points below, smaller spring wire diameter (for reduced mass) will - and we can disagree about this - result in lower spring rates. Even though the last bullet point mentions "stiffer bars and springing" it does not specify in comparison to VE, and I'm assuming it refers to lower level (FE1/FE2) VF models.

The one thing I struggle to reconcile is the mass-reduction efforts implemented in VF, based on the most-common brake packages found on these vehicles - 321mm front/324mm rear for the previous generation G8 and both VE/VF Holden "standard" V8 models, and 355mm front/324mm rear for 2014 SS. Along comes 2015, and suddenly a rear 360mm rotor and 4 piston caliper gets added to the SS/Lowndes special variants, as if mass no longer matters....especially on the unsprung side of the equation.

So, I'm of the belief that, like the Firebird TransAm WS6 from the mid-70's (the Herb Adams years), a relatively soft spring package combined with stiffer sway bars approach was taken in the course of re-tuning the VF platform. There are obvious differences--imagine VF with nice squishy 70 or possibly 60-series tires!

The revised VF platform allowed this to be implemented, and the move to a DA bar in the rear (front is DA already) is a refinement of the product, and now part of the SS. Tires--both width and aspect ratio, wheel widths, and shock tuning play a much bigger part today, but the stiff spring/soft bar approach is generally less desirable, since tire profiles are so much lower than 40 years ago. Softer springs and more refined corner damping are what make it possible to have a vehicle with such low profile tires maintain a reasonably comfortable ride today.

In case anyone is not clear on the term Direct Acting in regard to sway bars, it means that the link to and working end(s) of the bar respond based on actual wheel motion/displacement -- whatever amount of movement of the suspension member(s) occurs, the bar arm at the link point moves that same distance. On most GM cars (take a B-body front suspension, for example) the end link of the sway bar is moving only part of the distance of the knuckle/ball joint, since the link is well-inboard of that position. To generate the same resistance effect of a DA bar, if one was possible, requires a larger diameter bar - realize that a sway bar/stabilizer shaft is a torsion spring that adds to the dynamic spring rate, thus has to be allowed for in damper (shock absorber) tuning.

Examples of DA bars on GM vehicles in the past:

- Beretta GTZ used a DA front bar (mounted on McPherson strut) - bar is MUCH smaller than the standard front bar linked to lower control arms

- Pontiac Grand Prix GXP used a DA front bar (mounted on Bilstein strut) - again, bar is significantly smaller than the standard bar

To me, this suggests that where chassis design allows it, and the engineers can overcome the bean counters, the preferred bar configuration will be a direct-acting setup.

Released: VF Commodore Technical Details

Here are selected quotes from the linked story:

  • Monroe Shocks installed new equipment to double-coat coil springs allowing a thinner wire for reduced weight.
  • Rear sway bar links are crossbolted with extra fasteners in V8 models.
  • Evoke now uses larger anti-roll bars, and on Sports V8 models these are much larger, including an 18mm rear bar. Newly-developed tyres from Bridgestone with different sidewall characteristics maintain comfortable ride and great grip with precise steering and stability despite firmer overall settings.
  • In every case, and there are more, not only was a weight loss targetted, but the resulting component also had to meet strength and durability requirements as well as being improved in it's primary function and aid in NVH suppression.
  • Finally - and yes America, this is the basis of the Chevrolet SS - is the SS-V Redline. It has stickier 245/40 and 275/35 f/r wheels on 8.5 and 9.0" rims, FE3 suspension which has stiffer antiroll bars and springing,
 

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Off Topic

Interesting you should bring up Herb Adams. Back when, I bought his Cheverra front fenders and quarter flares for my '79 Z/28. When it came time to get the nose it was no longer available, he and I went a few rounds over it because it was never mentioned, at the time of purchase for the other parts, that it was to be dropped from production.

Still, I had quite a few suspension parts from him for the Camaro. As you mentioned, his philosophy of soft spring/big bar is still around.

For those that don't know ..... Herb Adam's Chevy VSE Cheverra Reloaded - Hot Rod Magazine an update and history. The car was fast for the day, today, not so much, technology moves on even if we don't.

Here's an article from 1981 Hotrod mag that did a test between the two schools of hustle using 2nd gen F Body www.74-77Camaro.com

And 3rd Gen Guldstrand vs adams shootout '82 - Third Generation F-Body Message Boards

Today, with the updates to suspension design, IE, rear independent rear suspension, not sure if that holds true. Some think that by adding ANY rear sway bar takes away from the independence of one wheel to the other. The designers of the vette use the leaf spring in a design to reduce the sway bar diameter, by the way it's mounted, and yet stills have a good ride, for it's intended use.

C5/C6 Corvette Suspension Tech: Coilovers vs. Leafs - Corvette Online

With all that, and getting back on-topic, I would prefer a sway bar that attaches as close to the wheel as possible. botch designs attach to the LCA, but, the SS, and 2010-12 Camaro mounted up by the bushing would require a bigger bar to transmit the same force as one placed further out.

I think rotor size is what restricts the use of the 2015 sway bar to the 2015, and why it's really bigger than the front. The smaller rotor of the 2014 SS and V6 Camaro would place the caliper too close to the spindle centerline and prevent the placement of the end link so far out.

Since the SS has cast iron rear spindles, my plan is to take the SS/1LE rear spindle, it's aluminum, and swap it, parking brake and all. This will fix a few things.

Lowers the unsprung weight, still get the Brembo rear caliper and larger rotor, and parts are readily available compared to the SS.

Someone with a '15 needs to get a wrench and go measure the SS bars, front and rear. My thinking is if the front is a different size, then the bars were changed due to the magnetic shocks, and possibly the springs. I know the vettes got different springs when the magnetic shocks.

I'd probably go with the 1LE/ZL1 rear bar and trim the spare tire well to fit.... it's plastic.
 

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Posted Dec 31 2013 <<click to view - some here may not have seen this. The article (linked below) only offers some specifics, so some things, as we've been discussing the sway bar, for example, may be based more on assumptions, hunches, or past experience/observation, even in other vehicles. At the point of the transition to VF, the direct-acting (DA) rear sway bar was found only on the Camaro in the Zeta family. That it has now been adopted for this particular VF application is something we've been speculating about.

My theory is that the chassis re-tune and mass reduction implemented in VF permitted/included an overall reduction in spring RATES relative to VE. As mentioned in the bullet-points below, smaller spring wire diameter (for reduced mass) will - and we can disagree about this - result in lower spring rates. Even though the last bullet point mentions "stiffer bars and springing" it does not specify in comparison to VE, and I'm assuming it refers to lower level (FE1/FE2) VF models.

The one thing I struggle to reconcile is the mass-reduction efforts implemented in VF, based on the most-common brake packages found on these vehicles - 321mm front/324mm rear for the previous generation G8 and both VE/VF Holden "standard" V8 models, and 355mm front/324mm rear for 2014 SS. Along comes 2015, and suddenly a rear 360mm rotor and 4 piston caliper gets added to the SS/Lowndes special variants, as if mass no longer matters....especially on the unsprung side of the equation.

So, I'm of the belief that, like the Firebird TransAm WS6 from the mid-70's (the Herb Adams years), a relatively soft spring package combined with stiffer sway bars approach was taken in the course of re-tuning the VF platform. There are obvious differences--imagine VF with nice squishy 70 or possibly 60-series tires!

The revised VF platform allowed this to be implemented, and the move to a DA bar in the rear (front is DA already) is a refinement of the product, and now part of the SS. Tires--both width and aspect ratio, wheel widths, and shock tuning play a much bigger part today, but the stiff spring/soft bar approach is generally less desirable, since tire profiles are so much lower than 40 years ago. Softer springs and more refined corner damping are what make it possible to have a vehicle with such low profile tires maintain a reasonably comfortable ride today.

In case anyone is not clear on the term Direct Acting in regard to sway bars, it means that the link to and working end(s) of the bar respond based on actual wheel motion/displacement -- whatever amount of movement of the suspension member(s) occurs, the bar arm at the link point moves that same distance. On most GM cars (take a B-body front suspension, for example) the end link of the sway bar is moving only part of the distance of the knuckle/ball joint, since the link is well-inboard of that position. To generate the same resistance effect of a DA bar, if one was possible, requires a larger diameter bar - realize that a sway bar/stabilizer shaft is a torsion spring that adds to the dynamic spring rate, thus has to be allowed for in damper (shock absorber) tuning.

Examples of DA bars on GM vehicles in the past:

- Beretta GTZ used a DA front bar (mounted on McPherson strut) - bar is MUCH smaller than the standard front bar linked to lower control arms

- Pontiac Grand Prix GXP used a DA front bar (mounted on Bilstein strut) - again, bar is significantly smaller than the standard bar

To me, this suggests that where chassis design allows it, and the engineers can overcome the bean counters, the preferred bar configuration will be a direct-acting setup.

Released: VF Commodore Technical Details

Here are selected quotes from the linked story:

  • Monroe Shocks installed new equipment to double-coat coil springs allowing a thinner wire for reduced weight.
  • Rear sway bar links are crossbolted with extra fasteners in V8 models.
  • Evoke now uses larger anti-roll bars, and on Sports V8 models these are much larger, including an 18mm rear bar. Newly-developed tyres from Bridgestone with different sidewall characteristics maintain comfortable ride and great grip with precise steering and stability despite firmer overall settings.
  • In every case, and there are more, not only was a weight loss targetted, but the resulting component also had to meet strength and durability requirements as well as being improved in it's primary function and aid in NVH suppression.
  • Finally - and yes America, this is the basis of the Chevrolet SS - is the SS-V Redline. It has stickier 245/40 and 275/35 f/r wheels on 8.5 and 9.0" rims, FE3 suspension which has stiffer antiroll bars and springing,
Are you implying that the rear set-up on the SS is NOT a DA set-up, because I would have to disagree. Other than the end link design, they both act directly on the LCA, just in different locations.

I don't think your comparisons of the Beretta and GP really prove anything, both use McPherson struts, both attach in the same manner. Just because the bar is smaller in the performance model, than the standard chassis, would usually indicate that your examples have stiffer springs. Many cars do this. The relation of spring/bar size tends to be directly related in OE setups. Small bar= stiffer spring, larger bar=softer spring. The vette does it, as an example. I think it's a ride Vs handling compromise and the OEs tend to lean towards stiffer springs.

It also goes back to my post above, and yours, of the stiff spring/small bar Vs. soft spring/larger bar and it seems GM prefers the stiff spring/smaller bar.
 
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