Cortex Torque Arm Racechrono Track Review

[NDSP]

So the whole time I'm reading through this thread, I'm remembering the the popular hotrodding article of different rear suspensions. Here is a part of what it said about torque arms.


When we asked mechanical engineer Katz Tsubai about what he felt were the pros and cons of torque-arm suspension he said, "One pro is that the system is kinematically free in roll. As with a three-link, the suspension is free to roll when Heim joints are used. As a result, tuning is much easier and the end result is predictable and won't surprise you by causing conditions like snap-oversteer." He also pointed out that it's possible to achieve good roll steer characteristics with a low roll center. Added benefits would be that the system is fairly simple to retrofit to an older car since you do not have to cut up the floor and trunk. Additionally, depending on the layout and centering device used, it's relatively easy to route a full exhaust system.

On the down side, Katz stated that he felt the system had a low anti-squat value, depending on how the trailing links were arranged and that it's difficult to get high anti-squat without causing roll oversteer or severe brake hop. This would be more of a problem in a short-wheelbase car that would use a relatively short torque arm. Kats also related that in some cases the system has limited adjustability. Since the length of the torque arm is fixed, any changes to adjust the anti-squat value will also change the roll steer characteristics. On the subject of decoupled torque-arm setups Katz added, "The idea is to free up the torque arm from reacting to braking torque by adding a telescoping auxiliary link. This allows you to have very high anti-squat value, while keeping brake hop, which is normally associated with high anti-squat, at bay. The system is very sensitive to tuning, particularly preloading."



Read more: http://www.popularhotrodding.com/tech/0604_rear_suspension_guide/viewall.html#ixzz2VkT7dkQX

 

[NDSP]

Here is a part of what it said about the three link system. And why I have, at least for now, decided to stay with the stock setup and not go torque arm.

One big advantage to using a three-link: there's virtually no bind associated with the design. Each link has one job and one job only. The two lower links working together prevent the axle from skewing relative to the vehicle axis and the upper link is responsible for controlling pinion angle changes in bump and droop. This allows the system to be set up for whatever type of driving you plan on doing, whether it's drag racing, road racing, or a combination of the two. When we asked Mark and Katz why they chose the three-link approach, they said, "Whether we want to accept it or not, all suspension systems are faced with compromise; you simply cannot have everything in one system that you'd like to. You need to make choices as to what is most important. In our opinion, the three-link approach arguably offers the fewest high-performance compromises of any rigid axle suspension system. In addition to being very simple and highly tunable, the three-link also provides the lightest unsprung weight--in a rigid-axle suspension--relative to all other setups. These facts are the reasons that the fastest road race rigid-axle cars predominantly use this setup, such as today's Trans Am and SCCA GT1 cars."

Mark was quick to point out that, like all rear suspensions, the three-link also has a couple of pitfalls. The biggest downfall with a well-executed three-link application on early musclecars is packaging. A good three-link setup will usually require some intrusion between the rear seats in the interior of the car for the upper link, though this can be minimized, and a custom rear seat can be installed that will easily accommodate clearance requirements. A quality three-link system will also set you back a good stack of cash. Lateral Dynamics Mechanical Engineer Katz Tsubai also added this in regards to three-links: "Not all three-links, or any other suspension configuration for that matter, are created equal. These advantages and disadvantages not only show you inherent characteristics of each configuration, but also design possibilities and flexibilities. The suspension is only as good as how you can implement those possibilities into the design. For example, let's say someone decides to build a three-link. His design consists of 10-inch long upper and lower links, all three mounted level to the ground, with a 20-inch Panhard bar mounted above the third member. Technically, it's a three-link and there is no roll bind, but it is hardly a good suspension system. Engineering, design, and execution are just as important as the suspension configuration itself."


Read more: http://www.popularhotrodding.com/tech/0604_rear_suspension_guide/viewall.html#ixzz2VkWT71jI

 

[55R2014]

Read more: http://www.popularhotrodding.com/tech/0604_rear_suspension_guide/viewall.html#ixzz2VkT7dkQX

Thank you for the link to the article. Great information.

 

[barbaro]

Here is a part of what it said about the three link system. And why I have, at least for now, decided to stay with the stock setup and not go torque arm.

One big advantage to using a three-link: there's virtually no bind associated with the design. Each link has one job and one job only. The two lower links working together prevent the axle from skewing relative to the vehicle axis and the upper link is responsible for controlling pinion angle changes in bump and droop. This allows the system to be set up for whatever type of driving you plan on doing, whether it's drag racing, road racing, or a combination of the two. When we asked Mark and Katz why they chose the three-link approach, they said, "Whether we want to accept it or not, all suspension systems are faced with compromise; you simply cannot have everything in one system that you'd like to. You need to make choices as to what is most important. In our opinion, the three-link approach arguably offers the fewest high-performance compromises of any rigid axle suspension system. In addition to being very simple and highly tunable, the three-link also provides the lightest unsprung weight--in a rigid-axle suspension--relative to all other setups. These facts are the reasons that the fastest road race rigid-axle cars predominantly use this setup, such as today's Trans Am and SCCA GT1 cars."

Mark was quick to point out that, like all rear suspensions, the three-link also has a couple of pitfalls. The biggest downfall with a well-executed three-link application on early musclecars is packaging. A good three-link setup will usually require some intrusion between the rear seats in the interior of the car for the upper link, though this can be minimized, and a custom rear seat can be installed that will easily accommodate clearance requirements. A quality three-link system will also set you back a good stack of cash. Lateral Dynamics Mechanical Engineer Katz Tsubai also added this in regards to three-links: "Not all three-links, or any other suspension configuration for that matter, are created equal. These advantages and disadvantages not only show you inherent characteristics of each configuration, but also design possibilities and flexibilities. The suspension is only as good as how you can implement those possibilities into the design. For example, let's say someone decides to build a three-link. His design consists of 10-inch long upper and lower links, all three mounted level to the ground, with a 20-inch Panhard bar mounted above the third member. Technically, it's a three-link and there is no roll bind, but it is hardly a good suspension system. Engineering, design, and execution are just as important as the suspension configuration itself."


Read more: http://www.popularhotrodding.com/tech/0604_rear_suspension_guide/viewall.html#ixzz2VkWT71jI

No bind in a three link design? Griggs and Filip are mechanical engineers as well. Further they have specific experience with this car. Third my subjective experience having owned and modded three S197s tells me that the three link is vastly inferior to a Watts link, torque arm, heim jointed lower control arm rear suspension. And also that bind is greatly reduced. As for adjustability; the Cortex Watts link to which the Torque arm is attached is the most adjustable Watts link on the market. In my case both squat and brake dive were greatly reduced as was a reduction of body roll during cornering.

 

[Whiskey11]

No bind in a three link design? Griggs and Filip are mechanical engineers as well. Further they have specific experience with this car. Third my subjective experience having owned and modded three S197s tells me that the three link is vastly inferior to a Watts link, torque arm, heim jointed lower control arm rear suspension. And also that bind is greatly reduced. As for adjustability; the Cortex Watts link to which the Torque arm is attached is the most adjustable Watts link on the market. In my case both squat and brake dive were greatly reduced as was a reduction of body roll during cornering.

Which of your three S197s had the fully heim jointed rear suspension on it?

They are correct after all. The only bind in a 3 link is from the bushings used. Remove the bushings and replace with something that can articulate without bind and the system becomes bind free. This would be accomplished with a heim joint in each end of the control arms and at the differential bushing.

I would gladly argue that the Cortex Watts link is not as adjustable as you make it out to be. It is limited by the height of the differential cover in it's range of adjustment. The Fays2 unit gives you a lot more places to put the rear roll center and can, should you chose, get it higher than that of the Cortex unit. I have 7 different places the roll center can be put at, the Cortex unit has 4.

That isn't to say that the Cortex unit isn't a high quality kit, just that it isn't the most adjustable Watts link on the market.

I'm not sure I follow how a torque arm would reduce body roll while cornering. Kinematically freeing the rear axle in roll and removing the bind in the upper 3rd link would actually make it roll more since you've reduced the roll resistances caused by bushing bind. What I can see impacting the roll is the watts linkage having a higher roll center than the PHB would in your lowered ride height. That is a reasonable explanation of what you are experiencing.

This might be an area in which I can help the discussion when I get my Torque Arm. I have a year and a half of Fays2 Watts link use on the stock 3 link and about 100 runs in autocross with it. There will be some subjectivity associated with removing the 3rd link and swapping it for something in the aftermarket but what wont be as subjective is how the body pitches and rolls during acceleration, braking and cornering as those will be very real assessments of how the car drives.

 

[Norm Peterson]

I think there is a little lateral load transfer happening as a consequence of UCA plan view rotation in roll plus its axial load under acceleration, and the vertical separation between the UCA and the PHB. It's on the order of 5 lbs with both UCA pivots spherical, and probably little more than noise as far as those of us who don't get paid good $ to drive hard all day are concerned. I have not tried to model the added effect of UCA bushing stiffness, as I don't have any good, readily-usable data to work with. But if you're bottoming the bushings with wheel hop on corner exit your main problem isn't the car's rear suspension.


Norm

 

[sheizasosay]

I think there is a little lateral load transfer happening as a consequence of UCA plan view rotation in roll


Norm

Caused from the arc of a PHB? If a watts is used, seems it would mitigate that as much as possible.

 

[barbaro]

Which of your three S197s had the fully heim jointed rear suspension on it?

They are correct after all. The only bind in a 3 link is from the bushings used. Remove the bushings and replace with something that can articulate without bind and the system becomes bind free. This would be accomplished with a heim joint in each end of the control arms and at the differential bushing.

I would gladly argue that the Cortex Watts link is not as adjustable as you make it out to be. It is limited by the height of the differential cover in it's range of adjustment. The Fays2 unit gives you a lot more places to put the rear roll center and can, should you chose, get it higher than that of the Cortex unit. I have 7 different places the roll center can be put at, the Cortex unit has 4.

That isn't to say that the Cortex unit isn't a high quality kit, just that it isn't the most adjustable Watts link on the market.

I'm not sure I follow how a torque arm would reduce body roll while cornering. Kinematically freeing the rear axle in roll and removing the bind in the upper 3rd link would actually make it roll more since you've reduced the roll resistances caused by bushing bind. What I can see impacting the roll is the watts linkage having a higher roll center than the PHB would in your lowered ride height. That is a reasonable explanation of what you are experiencing.

This might be an area in which I can help the discussion when I get my Torque Arm. I have a year and a half of Fays2 Watts link use on the stock 3 link and about 100 runs in autocross with it. There will be some subjectivity associated with removing the 3rd link and swapping it for something in the aftermarket but what wont be as subjective is how the body pitches and rolls during acceleration, braking and cornering as those will be very real assessments of how the car drives.

You might be right about the Fays II. As for the body roll. First, I had a three link on my current vehicle with an adjustable panhard rod, steeda sport springs and and BMR lower control arms with relocation brackets. I replaced the Panhard with the Watts Link. I noticed the car set faster in a chicane. That was it.

I then put the torque arm on with heim jointed lower control arms on the axle end only. And everything changed. The car cornered flatter. Less body lean. Before the car seemed to handle in two parts. I would turn the wheel and the front end would turn and then I would wait a split second to see what the back end would do.

With the TA and The new lower control arms, the rear end follows the front end and the car handles as one unit rather than two with me being the link in between. The impression it gives the driver is that there is less body roll/lean. Now before everyone jumps on me I didn't measure it. And I would not know how. But that is the best way I can explain it subjectively.

If you want to ascribe it all to the heim jointed lower control arm. I would say I have had those on a previous S197 along with an aftermarket adjustable upper control arm and that car did not handle like this. Not that the previous car handled badly but it did not have the precision of the current set up. My previous S197 cornered flat but the springs were much stiffer to achieve the result, and ride quality suffered accordingly. Also, this current improvement in handling occurred despite going to taller and softer Boss 302 springs. The ride quality has improved. The car just drive smoother. I cannot quantify it.

The car is flatter in response to all stresses whether it be cornering, braking or acceleration. This is not just my opinion but the opinion of everybody who has a torque arm and is the reason they have it. In my universe that is about 7-8 people and the number is growing. I have tried several three link combinations and nothing comes close to what I have inexpertly described. In addition, the aftermarket adjustable upper control arms also denigrated ride quality to an unacceptable level.

Mechanical engineers not familiar with our platform can speak theoretically about what a torque arm might do on a hypothetical car. I can say though unequivocally that the rear suspension setup of watts link, a one end heim jointed rear lower control arm and a torque arm is superior to any traditional three link setup I have ever driven and is also very streetable. That is my subjective judgment and I invite you to see for yourself and I am interested to see how Whiskey likes his setup.

 

[Norm Peterson]

Caused from the arc of a PHB? If a watts is used, seems it would mitigate that as much as possible.

I was ignoring that because that effect is a lot smaller.

Think in terms of chassis roll moving the chassis side UCA pivot laterally (because it is located several inches above the PHB). The axial UCA load then has a smallish lateral force component in an anti-roll sense (working against the PHB to generate a smallish anti-roll moment).

A (much) longer UCA would reduce this, but at 5 lbs or so LLT it seems hardly worth it for anything short of the really pointy end of competition.


I haven't tried to assess any anti-roll effects of a TA as a consequence of its resistance to axle steer (trust me, this exists), though I cannot see even the complete elimination of the above 5 lbs constituting a night and day difference.


Norm

 

[Norm Peterson]

I would turn the wheel and the front end would turn and then I would wait a split second to see what the back end would do.

With the TA and The new lower control arms, the rear end follows the front end and the car handles as one unit rather than two with me being the link in between. The impression it gives the driver is that there is less body roll/lean. Now before everyone jumps on me I didn't measure it. And I would not know how. But that is the best way I can explain it subjectively.

I think what I'm hearing here is tied to the time difference between geometry effects and elastic effects. Anti-squat is a geometric effect and happens instantaneously (though its full effect does have to wait for some tire deformation to occur, but that's still happening before spring compression and however much squat does). These are things that happen at the tens of millisecond level over a total time span of a quarter to maybe half a second, so you sense them coming in at different times rather than being able to mentally measure what's going on.

No doubt it bothers some people more than others, and different people may be noticing slightly different situations where geometric vs elastic timing is happening. Kind of like roll - some people are bothered by this a lot more than others.

I consistently noted a little uncertainty exiting T1 at NJMP's Lightning, an odd little twitch that didn't quite threaten to go all loose at whatever speed I was carrying. T1 is a right hander that crests a hill, so the suspension tends to unload at the apex and re-load on exit. T5 at that track is similar, but with a sharper hill profile it's a bit slower and you can't get into the throttle as hard as early or you will spin (or go 4-off in T6) and I never noticed it there. OE springs, for whatever that's worth.

Unfortunately, I have no TA-equipped car experience there to even guess whether there would be any difference.


Norm

 

[sheizasosay]

This probably deserves it's own thread...with a spotlight and good night this shit is tight! I remember Filip saying he was developing a SLA, but I never seen any of the pics. He just said that he would release it once he has beat it to death and verified it through racing abuse.... ok so check the link...grab a little bib and tuck it in and enjoy (hope everybody hasn't seen this a long time ago and I'm late)

http://www.youtube.com/watch?v=Cm2QKbuM3OY

 

[NDSP]

That is nice, I image pricey too.

Sent from my ASUS Transformer Pad TF700T using Tapatalk 2

 

[55R2014]

I saw that k-member mocked up on a car in his shop a while back. It looked pretty stout.

 

[2013DIBGT]

Hello, I have been following this thread with interest because I am about 86.7757575% sure that I will be installing a suspension kit that also includes a Torque Arm/Watts Link combo like the Cortex setup but in my case it will most likely be the Griggs GR40SS kit.

I'm curious to hear what the general consensus is on why these rear end packages offered by Cortex & Griggs focus in on swapping out the rear spring/shock combo for a coilover?

I see the original poster has chosen to not use a rear coilover setup on his car so I guess its safe to assume that a coilover is not a requirement when using a Torque Arm.

My original thought for the use of the coilover was that it is mainly because they offer a means to corner balancing the car? Besides corner balancing, what are the short falls, if any, of using a standard rear spring/shock combo with these kits?

Another question to the OP, did you purchase the "Quiet/Street" components in your kit? Do you run or intend to run slicks at the drag at any point? If so, do you have any concerns with having a urethane bushing in the rear control arm verse a full Heim setup?

Thanks for the interesting post on this topic and any additional info you can provide.

 

[sheizasosay]

Hello, I have been following this thread with interest because I am about 86.7757575% sure that I will be installing a suspension kit that also includes a Torque Arm/Watts Link combo like the Cortex setup but in my case it will most likely be the Griggs GR40SS kit.

I'm curious to hear what the general consensus is on why these rear end packages offered by Cortex & Griggs focus in on swapping out the rear spring/shock combo for a coilover?

I see the original poster has chosen to not use a rear coilover setup on his car so I guess its safe to assume that a coilover is not a requirement when using a Torque Arm.

My original thought for the use of the coilover was that it is mainly because they offer a means to corner balancing the car? Besides corner balancing, what are the short falls, if any, of using a standard rear spring/shock combo with these kits?

Another question to the OP, did you purchase the "Quiet/Street" components in your kit? Do you run or intend to run slicks at the drag at any point? If so, do you have any concerns with having a urethane bushing in the rear control arm verse a full Heim setup?

Thanks for the interesting post on this topic and any additional info you can provide.

I think they relocate the shocks/coilovers to make room for more tire. Seems I remember reading that on Grigg's site(might want to check that). There may be other benefits for going to the relocated coilovers on the rear.

 

[zeroescape]

Switching to a coilover is for tuning purposes. The spring and shock mounted together mean they travel the same distance, whereas in stock configuration the shock will have more motion than the spring when side loads occur.

Also theres more options for spring rate changes if you decide to, whereas you see on countless forums people trying to compare all sorts of lowering springs and their ambiguous spring rates.

 

[Whiskey11]

I think they relocate the shocks/coilovers to make room for more tire. Seems I remember reading that on Grigg's site(might want to check that). There may be other benefits for going to the relocated coilovers on the rear.

If anything, relocating the springs to the shocks is actually reducing wheel/tire room since you now have the width of the spring to add to the shock.

The real reason they move to coilovers in the rear (as apposed to weight jackers with coilover springs in 99% of the other kits on the market) is for motion ratios. Specifically it's easier to match shock valving to the wheel rate as you don't have to worry about the motion ratios of having the springs inboard of the shocks.

No they wouldn't be required with the torque arm or watts link setup.

 

[DTL]

I have threaded body shocks on the rear of my car, but I still run springs in the stock location. Coil over springs on the rear take up a lot of space that could be filled with wheel and tire. At least 2 companies sell weight jacks for the rear that allow you to run 2.5" coil over springs on the axle in the stock location and adjust ride height and corner weight.

 

[SoundGuyDave]

Motion ratio... Do the math, and for a given spring rate, look at the effective wheel rate for both longitudinal and later acceleration... The numbers are eye-opening.

 

[sheizasosay]

Motion ratio... Do the math, and for a given spring rate, look at the effective wheel rate for both longitudinal and later acceleration... The numbers are eye-opening.

You started a thread about that didn't you?