Cortex Torque Arm Racechrono Track Review

Whiskey11

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Really? Whiskey11, who just installed a torque arm on a "lightly-modded street car," apparently would beg to differ:

The difference certainly isn't immediately noticeable. About the only two things immediately noticeable was the increase in gear noise ("normal" with the removal of one bushing and the stiffening of another) and the sensitivity to throttle input. The car requires a little different car setup which I will be playing with on Saturday and I'm sure with the front bar stiffer, or the rear bar removed or a combo of both the car is going to change and who knows, maybe I'll be able to jump on the throttle sooner like I had hoped I would be able to without inducing terminal understeer? Maybe my high rear roll center has something to do with it? I honestly don't know.

EDIT: No matter what, I'm determined to make the car work around this suspension now because I've invested the money into the setup. It wasn't a cheap investment and it's waaaay too soon to just write it off. Maybe with some tweaking, maybe a few calls to Filip to see if he has any suggestions and I'll decide from there what to do with it. Chances are the next time it is coming off is when I sell this car for the next gen Mustang. The simplicity of an IRS setup makes me happy! :p Coilovers, swaybars, wheels, tires, go! :)
 
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sheizasosay

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I would consider dropping the rear roll center whiskey. Unless that is a bigger pain then ditching the rear sway.

I think you would do yourself justice in keeping the TA and getting tips from Filip. Worst case scenario Barbaro already said he'll buy it off you if you don't like it.
 

barbaro

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Really? Whiskey11, who just installed a torque arm on a "lightly-modded street car," apparently would beg to differ:

I noticed you changed the quote in your signature. You are evolving. As for Whiskey, he is not running the recommended setup. He is not running mine. So on my side is Bruce Griggs, Filip Trojanek, Revan Racing, Chris Corbetto and on your side you have Norm (maybe), Whiskey 11 ( maybe), Strano. I am comfortable with the company I keep and you are free to disagree.
 

Whiskey11

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I would consider dropping the rear roll center whiskey. Unless that is a bigger pain then ditching the rear sway.

I think you would do yourself justice in keeping the TA and getting tips from Filip. Worst case scenario Barbaro already said he'll buy it off you if you don't like it.

Roll center is definetely harder than the swaybar. The bolt is in the top hole and there is zero way to get it out of there without dropping the Watts frame. If the bar setting tweaks dont work then I will drop the RC but not before testing these other options. I am lazy like that. :)

As for being on anyones side... I am on my own side and make judgements based on experience and info I gather from others. Neither Terry, nor Sam, nor Norm, nor SkyRender, etc recommend a TA setup and I sure as hell didnt decide based on your experience. I am sure both Sam and Terry would disapprove of my choice in Coilovers. It isnt that I dont trust their setup experience (both are more capable than I am) but I learn by doing and it is the expensive way. Ironically, I would be testing more if I had more disposable income. I value their experience though and have used all of that in my own build.

I am undecided on the TA issue. Recommended setup or not, YOU said it was the single most transformative mod on your car and that experience certainly is not mine. That isnt to say I hate it either.
 
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Sky Render

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As for Whiskey, he is not running the recommended setup. He is not running mine. So on my side is Bruce Griggs, Filip Trojanek, Revan Racing, Chris Corbetto and on your side you have Norm (maybe), Whiskey 11 ( maybe), Strano. I am comfortable with the company I keep and you are free to disagree.

But you previously said that a street car with fewer modifications would notice MORE of a difference using a Torque Arm.
 
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Ivan 5.0

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We were racing this weekend again at Summit Point

I was at Summit last weekend, too! Running HPDE. I had the black mustang with the plates "5 DOT 0" :highfive:

IMG_1621.JPG
 
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Norm Peterson

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Thanks Norm, I look forward to your results. :)
Working just from the LCA numbers (-.4375" at the axle, -2.3175" at the chassis), I'm getting 18.3% for the 3-link and 34.2% for the TA statically with no driver aboard.

Add enough driver weight to drop the ride height another 0.31" and the A-S percentages look like 17.5% (3-link) and 25.3% (TA).

I wouldn't worry too much about the difference in tire height differing. I'm not using that to compute Z-axis (vertical) numbers, and this varies a bit from mfr to mfr and from the "theoretical" tire dimensions pulled from tire size designations anyway.


Norm
 
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Whiskey11

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Working just from the LCA numbers (-.4375" at the axle, -2.3175" at the chassis), I'm getting 18.3% for the 3-link and 34.2% for the TA statically with no driver aboard.

Add enough driver weight to drop the ride height another 0.31" and the A-S percentages look like 17.5% (3-link) and 25.3% (TA).

I wouldn't worry too much about the difference in tire height differing. I'm not using that to compute Z-axis (vertical) numbers, and this varies a bit from mfr to mfr and from the "theoretical" tire dimensions pulled from tire size designations anyway.


Norm

Interesting that the TA lost almost 10% from a .31 ride height drop and the 3 link didnt lose that much. Downside to constraining the IC to the plane perpendicular to the TA angle at the chassis mount. Now I want to go play with the calculator again and see what happens with "level" lca's from relocation brackets!
 

FullAhead

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EDIT: shouldn't post while intoxicated.

...don't mind the new guy over in the corner.
 
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sheizasosay

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Roll center is definetely harder than the swaybar. The bolt is in the top hole and there is zero way to get it out of there without dropping the Watts frame. If the bar setting tweaks dont work then I will drop the RC but not before testing these other options. I am lazy like that. :)

Damn, it's all the way at the top? I'm probably not telling you anything you don't know, but just incase....the difference in the effects of rear RC vs swaybar are similar in dialing in and out of oversteer, but the actualy characteristics of how it feels and works is a little different from my understanding. I think effects happen much, much quicker with RC adjustments vs swaybar adjustments. RC height changes are gonna have weight transfer changes basically immediately and the car "should" do things a little quicker in the "set" and also if it was gonna oversteer or not. Swaybar change is gonna be based on however long the bar takes to ramp up on the spring rate/wheel rate via rear suspension travel. I'm pretty sure Norm will elaborate if I talk non-sense. I have heard people on engineer forums (eng-tips or similar?) refer to the rear roll center adjustment as thinking of the RC height as a "fast swaybar". I have also heard that a properly setup race car shouldn't need a rear swaybar (or maybe no sway at all?). You and I both know there is about a bazillion ways to get to the end result in regards to suspension. Just food for thought.

I would tell you to enjoy tinkering with your new toys, but you have made that watts sound like a major PITA. Quick question: how many bolt holes does it have for RC adj and which ones are actually accessible without an act from congress?
 

csamsh

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Not mustang, but related: Rear sway bar on Porsche 962

DSC010871328397860.jpg
 

Whiskey11

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Damn, it's all the way at the top? I'm probably not telling you anything you don't know, but just incase....the difference in the effects of rear RC vs swaybar are similar in dialing in and out of oversteer, but the actualy characteristics of how it feels and works is a little different from my understanding. I think effects happen much, much quicker with RC adjustments vs swaybar adjustments. RC height changes are gonna have weight transfer changes basically immediately and the car "should" do things a little quicker in the "set" and also if it was gonna oversteer or not. Swaybar change is gonna be based on however long the bar takes to ramp up on the spring rate/wheel rate via rear suspension travel. I'm pretty sure Norm will elaborate if I talk non-sense. I have heard people on engineer forums (eng-tips or similar?) refer to the rear roll center adjustment as thinking of the RC height as a "fast swaybar". I have also heard that a properly setup race car shouldn't need a rear swaybar (or maybe no sway at all?). You and I both know there is about a bazillion ways to get to the end result in regards to suspension. Just food for thought.

I would tell you to enjoy tinkering with your new toys, but you have made that watts sound like a major PITA. Quick question: how many bolt holes does it have for RC adj and which ones are actually accessible without an act from congress?

Indeed, there is about a dozen ways to do what I want the car to do and I actually think that if your "fast" and "slow" swaybar theory is correct that leaving the RC higher and either increasing the front or decreasing the rear or a combo of both is the better move. The issue here isn't necessarily a steady state oversteer, it's actually pretty close to neutral (read: I'm not driving hard enough :p) with constant throttle. However, trying to get on the throttle earlier, like a Torque Arm is supposed to allow, almost always results in the car stepping out. A few theories:

1.) I'm using the friction circle better, maybe even because torque arms are "easier to drive hard" and there just is no rear grip to do that with.

2.) Too much rear spring rate

3.) Too little front spring rate

4.) Driver is not being smooth.

I'm willing to bet it's a combo of all of these so I'd like to add a touch of rear grip, somehow to be more aggressive with the throttle. I'd like the car to step out at WOT and maybe 85%-90% throttle but when I'm ramping from being off throttle to on the throttle there shouldn't be an instant stepping out of the rear of the car.

The test'n'tune should provide the ability to tweak as necessary all while getting times!

As for the Watts link, basically to pull the frame is four bolts: The two PHB brace bolts on the driver side, the PHB brace bolt on the passenger side and the PHB bolt on the passenger side frame. Only once those are removed can the watts link be lowered enough to get a wrench on the center pivot bolt. Remember, that center pivot bolt is torqued to 100 lb*ft and it isn't easy to get off the car while you are on your back changing it. Once that is done you still have to torque everything back down while under the car.

Now that I've swapped from the stamped steel diff cover to the aluminum finned one, it basically requires frame removal to lower the RC height since the diff cover is A LOT closer to the watts link.
 

Norm Peterson

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Interesting that the TA lost almost 10% from a .31 ride height drop and the 3 link didnt lose that much. Downside to constraining the IC to the plane perpendicular to the TA angle at the chassis mount. Now I want to go play with the calculator again and see what happens with "level" lca's from relocation brackets!
Antisquat for a TA is nearly always more sensitive to changes in ride height than a 3-link (or a triangulated 4-link, which has the same anti-squat geometry as the 3-link). This is a consequence of the SVIC not being able to migrate very far longitudinally, while it still has to lie on the LCA side view axis projection and which varies considerably more in the vertical direction. This sensitivity is almost certainly part of why TAs are more sensitive to brake hop, because the anti-lift increases at a similarly "fast" rate as the rear suspension unloads and the rear rises.

A 3-link configured like the OE S197 results in the SVIC migrating longitudinally a lot more as ride height is varied in exchange for providing an anti-squat curve that's significantly less sensitive to changes in ride height over the usable suspension travel.


Changes in the rear roll center height also introduce changes in axle steer unless the LCAs are perfectly parallel in plan view (putting their "intersection" out toward infinity).


Norm
 
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Whiskey11

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Changes in the rear roll center height also introduce changes in axle steer unless the LCAs are perfectly parallel in plan view (putting their "intersection" out toward infinity).


Norm

New thing to go look up! This was the one thing that Jim Fays' explanation of his Watts link didn't make sense to me. I get that a higher roll center is less body roll, is that what is changing the axle steer or is there some other voodoo magic going on? Our LCA's are definitely not parallel in plan view, they skew outwards slightly towards the axle IIRC.
 

sheizasosay

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My money is on #1. I bet your tire is max traction laterally and doesn't have anything left to give.

Given no foul rear stear, I'm sure there is a point at a certain AS% that in the same scenario of early throttle that you will understeer from so much rear bite; I just don't think it's gonna happen at 31% AS. Guessing. Good luck! I'm gonna tap out and stop talking now.
 

Norm Peterson

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New thing to go look up! This was the one thing that Jim Fays' explanation of his Watts link didn't make sense to me. I get that a higher roll center is less body roll, is that what is changing the axle steer or is there some other voodoo magic going on?
Sort of. Axle steer is defined by the slope of a line constructed through two points representing the axle's lateral constraint. The intersection of the LCAs is one, for a symmetrically located PHB it's the midpoint of the bar, and for a Watts link it is the main pivot. For those last two, you use the actual longitudinal location rather than projecting that height back to the axle centerline.

Related side note - where this construction line crosses the vertical-transverse axle plane is really where the geometric roll center lies. It's close to but not exactly at PHB mid height or WL main pivot height.


Our LCA's are definitely not parallel in plan view, they skew outwards slightly towards the axle IIRC.
You sure about that?


Norm
 

kcbrown

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So far, what I'm getting is that the 3 link setup is capable of being at least as good as the torque arm setup when the 3 link setup makes use of Heim joints or some other equivalent mechanism to eliminate bind.

But my question is this: if you're constrained to use at least some type of bushing to eliminate NVH, and thus are forced to introduce bind into the system, does the torque arm suddenly have a notable advantage? If so, what, where, and by how much?

Like barbaro, I'm also interested in running with a relatively compliant suspension, because my car will be primarily a daily driver. But within that constraint, I want it to be as competent a car as I can possibly make it. I want it to feel as responsive and be as controllable as possible as long as doing so doesn't require that I significantly compromise the ride quality relative to stock. I'm willing to go with coilovers if doing so doesn't compromise suspension travel any more than springs which would lower the front by 1" and the rear by 1.5" would. I'm willing to use lower and upper control arm relocation brackets to retain the proper suspension geometry. I'm willing to use heim joints if doing so won't actually increase NVH by much, provided that doing so doesn't wind up being a maintenance headache.


Part of the problem is that I have yet to take delivery of my car (2014 GT with track package and Recaros), so I don't yet have a lot of experience with the stock suspension. I fully intend to gain that experience before making any suspension-related decisions. But the answer to the above hopefully won't require a lot of detail about the specifics of the setup. I suppose you could presume, for the purpose of answering the question, that I want the ride quality to be about the same as that of a stock Boss 302.


Hopefully my question won't be too distracting, because I'm finding the discussion thus far to be quite informative and interesting! :thumb:
 

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