Cortex Torque Arm Racechrono Track Review

[sheizasosay]

The function/job of the torque arm and UCA are the same. Control the effects of pinion rotation/climb.


AS is found by defining the rear instant center first (UCA and LCA "lines" intersect drawn from side view). Then drawing a line from the rear tire patch through the rear IC and continue that line until it reaches the front axle (vertical line drawn through the front axle). That point in relation to CG heigth determines AS. If its above the CG it's over 100% AS and vice versa.

Why do you want anti-squat? Anti-squat is only "in-effect" when the throttle is used right? If rear traction is the goal then run the softest spring possible to stay off the stops(per setup).

When you apply throttle with less than 100% AS the rear sinks(droops). If it sinks too far you're on the stops. Result is loss of traction. AS tuning here could be beneficial.

If you have greater then 100% AS then you essentially have the stiffest springs in the world as soon as you cross 100.1%. You better be straight.

AS varies during suspension travel as ride height affects both UCA/TA and the LCAs.

Tuning AS is done be changing ride heigth, UCA mount hole or UCA length, TA length and also LCA axle location (LCA brackets).

A problem I see is wanting a desired AS , having the vehicle at the ride height you want and corner weighted and left with trying to tune the AS with "one hole" in the UCA mount as an option or LCA brackets with a holes that may or may not be able to get you the desired AS without dialing in rear steer.

Does the TA have a benefit over the UCA in any of this tuning?

All yours to dissect and correct. Sorry, I couldn't afford the book.

Edit- if this info is correct I wish it would have been VERY early in the thread and my only input.

 

[Norm Peterson]

And as we can see, I'm still learning!

So that would mean that the IC still moves fore/aft a little (not just up and down) it's just that the fore/aft movement is constrained by the angle of the T/A and the height by the LCA's angle. Is that correct?

Sounds about right.


Norm

 

[Norm Peterson]

Why do you want anti-squat? Anti-squat is only "in-effect" when the throttle is used right?

Because A-S is a more immediate component of rearward load transfer - there's no waiting for the springs to find their new equilibrium position. The load transfer carried through the springs is actually the third and slowest component of load transfer to develop - dynamically there is load transfer through the shocks (bump damping) that peaks while the rear suspension is in the process of squatting. Of course, by the time the spring load has reached equilibrium, the shock loads have gone away (zero suspension velocity).

If rear traction is the goal then run the softest spring possible to stay off the stops(per setup).

When you apply throttle with less than 100% AS the rear sinks(droops). If it sinks too far you're on the stops. Result is loss of traction. AS tuning here could be beneficial.

There is a sort of balancing act going on here. "Softest spring" probably has to be taken in the context of how much A-S is present as well as vice-versa.

If you have greater then 100% AS then you essentially have the stiffest springs in the world as soon as you cross 100.1%. You better be straight.

Above 100% you get into what the drag strip guys call "separation", where the rear of the car actually rises. The springs are actually UNloading when this happens. The rear ride rate remains unchanged.

AS varies during suspension travel as ride height affects both UCA/TA and the LCAs.

Tuning AS is done be changing ride heigth, UCA mount hole or UCA length, TA length and also LCA axle location (LCA brackets).

Yes.

A problem I see is wanting a desired AS , having the vehicle at the ride height you want and corner weighted and left with trying to tune the AS with "one hole" in the UCA mount as an option or LCA brackets with a holes that may or may not be able to get you the desired AS without dialing in rear steer.

I'd say that the effect on axle roll steer would be a bigger issue with final-tuning the A-S via LCA inclination.

Does the TA have a benefit over the UCA in any of this tuning?

Not sure.


Norm

 

[dontlifttoshift]

Above 100% you get into what the drag strip guys call "separation", where the rear of the car actually rises. The springs are actually UNloading when this happens. The rear ride rate remains unchanged.

Norm

If a forces are high enough at instant center to push up on the car aren't those same forces pushing down on the tire resulting in increased traction? I always thought when the car squatted on acceleration, THEN it was unloading the springs.

 

[sheizasosay]

Above 100% you get into what the drag strip guys call "separation", where the rear of the car actually rises. The springs are actually UNloading when this happens. The rear ride rate remains unchanged.

Why would the rear ride rate not be infiniti? You can't compress it.



I'd say that the effect on axle roll steer would be a bigger issue with final-tuning the A-S via LCA inclination.

Totally agree. And if you have an adj UCA mount you have "one" other option for mounting. I was looking to see if the TA would be superior in that aspect.


Not sure.



Norm

What about this claim: "the first issue it solves is the back end getting overly upset over bumps. The UCA transmits that shock from the axle at about a 45 degree angle right into the chassis. That is the up and down motion everyone thinks is a unchangeable characteristic of the log axle. This alone give you tremendous confidence." I'll be honest, I'm not sure I have noticed an up/down. I have noticed an "in=out" plunge back and forth that can be most noticed at a very low rpm buck. I wrote that off to drivetrain slop.

Second claim: "the car becomes more stable under acceleration and braking regardless of road condition". This is all attributed to the TA.

Third claim I already addressed above in the "red" in regards to the car corners flatter. Anyway, that could have anything to do witht the TA?

Reference Barbaro's 13th post in "Cortex Torque Arm Review".

 

[Norm Peterson]

If a forces are high enough at instant center to push up on the car aren't those same forces pushing down on the tire resulting in increased traction? I always thought when the car squatted on acceleration, THEN it was unloading the springs.

Nope. While the car is in the process of squatting, the springs are compressing, which means that they have to be gaining load. However, this also means that the springs aren't carrying as much load as they will when the car finally gets to its equilibrium squatted position. Going back to the previous post about the geometric anti-squat effect happening the soonest in an acceleration squat event, you have to think dynamically. IOW think of these things in terms of how they vary with time, and think in very short time steps.


Norm
(having computer difficulties and I'm not going to type this a third time just to get two responses merged.)

 

[Norm Peterson]

What about this claim: "the first issue it solves is the back end getting overly upset over bumps. The UCA transmits that shock from the axle at about a 45 degree angle right into the chassis. That is the up and down motion everyone thinks is a unchangeable characteristic of the log axle. This alone give you tremendous confidence." I'll be honest, I'm not sure I have noticed an up/down. I have noticed an "in=out" plunge back and forth that can be most noticed at a very low rpm buck. I wrote that off to drivetrain slop.

Second claim: "the car becomes more stable under acceleration and braking regardless of road condition". This is all attributed to the TA.

Third claim I already addressed above in the "red" in regards to the car corners flatter. Anyway, that could have anything to do witht the TA?

Reference Barbaro's 13th post in "Cortex Torque Arm Review".

Stock, the UCA sits at less than 10° downhill to the chassis, and it's unlikely to ever go much past 20°. That makes the sine function times link load significantly smaller than implied, never mind that the UCAs main function is still pinion angle control. Maybe a little more force induced by the rotational inertia of the axle against the control arms now forcing pinion angle change to happen rather than the control arms keeping too much PA change from happening.

Over a one wheel bump with compliant rear control arm bushings, the rear axle probably does tend to dance around in 'steer' a little more with a 3-link, though, which would be more unsettling to the driver. I'm doing a little guessing based on 3-D visualization here, since I don't have the means to measure this. But the link loads would mainly come from the fore/aft horizontal force component, as the springs are still carrying the vertical force consistent with the axle's vertical position relative to the chassis.

About the second claim . . . perhaps. As far back as when Jaguars with stick axles were raced, there were experiments made with offsetting the upper link as a geometric means of equalizing rear tire load. If it's still up, Billy Shope's site has a calculator for this (as a matter of history, he was on the Ramchargers drag team back in the early 1960's).

Spring rate does not change no matter what the anti-squat is doing. But when you add more upward force at the rear from anti-squat than there is rearward load transfer (pushing down) from the acceleration the tail has to rise. It's really a force summation, not a geometric or other arbitrary limitation.

Keep in mind above all that the real-world visual of squat (or separation) occurring does not CAUSE load transfer - all it is, is visual confirmation that load transfer is happening and that the anti-squat is less than (greater than) 100%. At 100.0% A-S your visual observation tells you nothing about load transfer directly. I'm afraid that acceleration squat could be the poster boy illustration for how trying to describe something that's technical in nature using a "common sense/plain talk" approach only serves to confuse and mislead.


Norm

 

[Whiskey11]

Norm: According to my tape measure the Cortex Torque Arm has to be between 44.5" long to 45" long. That was obtained by hooking the end of the tape measure on the central support bearing of my stock 2 piece driveshaft since that is supposedly where the unit mounts to and measuring to the back of the differential (in this case there was a small "flange" that stuck out from the diff cover which I used as the rearward position). I think it might be a touch shorter than that though to clear the exhaust H-pipe but without having one here I couldn't say one way or the other though. I'm not sure if there is any other detail I can get you for measurements though!

Here is a video that Kelly (BMR Tech) posted over on Modded Mustangs of the stock 3 link moving around on a 2013 Mustang. It's from a drag run and launch:



Needless to say, I lost my appetite after viewing. I imagine it is worse on a shorter 2005-2010 arm!

 

[Roadracer350]

Is it me or is their a LOT of side to side and fore and aft movement...

 

[sheizasosay]

Is it me or is their a LOT of side to side and fore and aft movement...

I imagine a watts would help that some, but that is the reason why you want a stiffer and articulating joint.

That's a cool cam. I made one like that watching my rear watts and LCA's travel. I should do one with the UCA. Now to find a good mount...

 

[dontlifttoshift]

That's a cool video. Nothing there really bothers me other than the tons of wheel hop. I was paying particular attention to the rear bushing in the UCA expecting to see tons of movement relative to the mount and really didn't.

 

[sheizasosay]

That's a cool video. Nothing there really bothers me other than the tons of wheel hop. I was paying particular attention to the rear bushing in the UCA expecting to see tons of movement relative to the mount and really didn't.

I thought I saw some in the 20 second range. I tellya what does stand out is how much the UCA's angle changes (side view type).

 

[Mustang259]

Very cool video, it would be interesting to see if there really is a difference between stock and the popular aftermarket UCA's, that have articulating joints.
I was amazed at the amount of movement and now wonder about the durability of the stock UCA.

 

[stkjock]

Damn talk about seeing wheel hop.

 

[sheizasosay]

it would be interesting to see if there really is a difference between stock and the popular aftermarket UCA's, that have articulating joints.

I took you're request as a good excuse to order some more adhesive gopro mounts. They'll be here in a couple days. I'll mount it up and record the video in 720p 60 f/s and post it up. I got a J&M street extreme UCA riding in a BMR mount.

 

[Mustang259]

Cool, look forward to seeing it!

 

[Whiskey11]

Is it me or is their a LOT of side to side and fore and aft movement...

Keep in mind that the side to side movement you are seeing may be from the axle articulating as well as moving through the PHB arc. The reason I say that is because the UCA mount on the axle is going to move some side to side when the axle articulates because it is the highest point of the axle and the axle doesn't rotate about the UCA. That is what Norm was saying that the UCA does contribute some to the roll center when NOT using sphericals because of the bushing bind restricting how freely the UCA point moves side to side during roll.

That's a cool video. Nothing there really bothers me other than the tons of wheel hop. I was paying particular attention to the rear bushing in the UCA expecting to see tons of movement relative to the mount and really didn't.

You should pay attention to the FRONT UCA bushing then, because that is where all the deflection is occurring in the whole setup. It's disgusting to say the least.

I took you're request as a good excuse to order some more adhesive gopro mounts. They'll be here in a couple days. I'll mount it up and record the video in 720p 60 f/s and post it up. I got a J&M street extreme UCA riding in a BMR mount.

Zip-Ties make pretty good impromptu GoPro mounting solutions. That is how I got my under car shots on my YouTube channel. You could Zip-Tie the suction cup arm to the PHB Brace.

 

[neema]

How can you change pinion angle with the cortex unit? Spacers under the differential?

 

[DTL]

How can you change pinion angle with the cortex unit? Spacers under the differential?

You could run spacers, but that only gains you positive pinion angle. I don't see any way to go negative besides milling down the front stands that bolt through the webbing. I haven't found any need to adjust it as there's no pinion rise/climb to account for.

 

[Norm Peterson]

Nearly all all of that fore/aft motion is UCA bushing compliance, the rest is a function of chassis distortion (which you can also see as the floorpan sheet metal shakes). Hard to believe that that much movement would even be possible, but there it is. Figure nearly half happens at each UCA bushing . . . I don't think you can see the axle side "ear" all that clearly for all that hopping that's going on.

I doubt that the UCA length affects this motion itself very much, since it's mostly a bushing and chassis local flexibility thing. However, those same motions would affect the actual "effective" geometry at any given instant a bit more. At this point, you're talking about using a kinematic & compliance model to evaluate the differences rather than just simple geometry, and that's a whole lot more complex.

The lateral motion is almost certainly caused by the PHB arc forcing the axle to sashay back and forth as the suspension alternately squats as every gear hits and rebounds at the beginning of every upshift. There is enough squat going on to put the PHB inclination higher on the axle side at full squat, which means softish springs, plus maybe a little lowering and/or a pretty good size driver. You can see this because the axle recovers to the left on rebound, which only the PHB leveling back out on suspension rebound (rear end rise) can cause to happen.

The lateral motion actually isn't a whole lot, though the OE PHB bushings will permit slightly more relative lateral motion to occur than geometrically defined, due to some inertia effects in the lateral direction for both the axle mass and the sprung mass.


I'll bet $ that a repeat of that video with a spherical/spherical ended UCA and a Watts link would show a lot quieter behavior up there. Mostly I'd expect to see only the squat and the recovery.


DTL - I would hope that since PA control is pretty good with a TA that the TA would be fabbed to provide very close to an optimum PA setting. Just enough U-joint angle to keep all the little needle rollers in the joint rolling. Perhaps shimming the chassis side pickup down might be possible for very small adjustments in the negative direction if they were truly needed.


Norm