Cortex Torque Arm Racechrono Track Review

[Whiskey11]

I didn't know they used truck arms! I wa told they use TAs! Shows you how much I follow them!!

The only reason I know they use truck arms is because of a build thread over on Corner-Carvers.com where a guy put a Chevelle body on a NASCAR tube frame.

http://corner-carvers.com/forums/showthread.php?t=46268

Cool build to be honest!

EDIT: To the people turning this into a political shit storm. PLEASE STOP. Some of us are trying to learn something here...

 

[dontlifttoshift]

NASCAR runs truck arms.....those are another can of worms. In general truckarms drive good, but not "see Jesus" good.

 

[stkjock]

Cas

Get off the high horse.

I've asked and warned about this thread and the off topic BS, it's a tech section, we do not tolerate crap in tech.

I'm locking this for now. When I can I will clean it up and move the posts to a new threads for tech conversation and the BS seperately.

 

[stkjock]

thread re-opened


I cleaned the thread up - it maybe disjointed in a few spots, I was not taking the time to parse up posts, I already spent too much fucking time on this bullshit.

do not comment on this post, do not comment on any previous bullshit in the thread

ONLY COMMENT ON TECHNICAL QUESTIONS AND THE CONVERSATION AT HAND

 

[Roadracer350]

On a serious note tho those truck arms look like they would be a PITA to put on a mustang without a full chassis.

 

[Sky Render]

I posted this in the Truck Arm thread. This is a discussion of the various types of rear suspensions, including truck arms, torque arms, and 3-links.

The advantages of the torque arm, to me, seem minimal in light of the additional weight and the complexity needed to prevent brake hop.

http://www.popularhotrodding.com/tech/0604_rear_suspension_guide/viewall.html

 

[Norm Peterson]

TA Pros:
Fixed IC . . . fixed longitudinally (essentially), migrates vertically roughly double the change in rear ride height
Nearly bind free when built correctly . . . in roll, yes, but it does provide a little stiffness against axle steer
Fixed pinion angle . . . close, it's fixed with respect to the TA axis, which changes its inclination with rear suspension movement
One less shitty to replace bushing in the suspension
"Easier to drive"

TA Cons
Potential for brake hop on hard braking
Reducing antisquat as axle and body get closer, increasing anti lift as they separate (brake hop potential)
Added unsprung weight
Reduced ground clearance
Potential need for exhaust modifications

3 Link Pros
Simple antisquat tuning independent of roll steer
Less unsprung weight
Better packaging
Increasing antisquat as body gets closer to axle, decreasing anti lift as they separate (Norm is this true for the S197 at all?) . . . sort of. It's detail-dependent. You can make the 3-link A-S decrease with squat and increase with rise just like a TA without having to try too hard. Actually, the OE 3-link A-L does increase with an increase in rear ride height, just that it's a pretty slow effect. See thumbnail (it's as close as measurements to within less than ±0.1" are worth).

3 Link Cons
Walking IC (potential for instability over bumps?)
Added bushings in shitty to replace locations
PITA to swap out
Huge increase in NVH? . . . detail-dependent
Technically binds in roll/competes with geo roll center unless spherical/spherical ended


Norm

 

[martin_nj]

re timing system - i use a paid android app called trackmaster. very good results. i've been using it for 2 years now

 

[Sky Render]

re timing system - i use a paid android app called trackmaster. very good results. i've been using it for 2 years now

I use Trackmaster, as well. I recommend getting an external GPS unit, though. Most phones have pretty crappy resolution.

 

[martin_nj]

see i'm torn about that external sensor... i've used it with and w/out and for total lap time times i'm pretty happy.


on an autox course you might want more res tho

 

[Whiskey11]

TA Pros:
Fixed IC . . . fixed longitudinally (essentially), migrates vertically roughly double the change in rear ride height
Nearly bind free when built correctly . . . in roll, yes, but it does provide a little stiffness against axle steer
Fixed pinion angle . . . close, it's fixed with respect to the TA axis, which changes its inclination with rear suspension movement
One less shitty to replace bushing in the suspension
"Easier to drive"

TA Cons
Potential for brake hop on hard braking
Reducing antisquat as axle and body get closer, increasing anti lift as they separate (brake hop potential)
Added unsprung weight
Reduced ground clearance
Potential need for exhaust modifications

3 Link Pros
Simple antisquat tuning independent of roll steer
Less unsprung weight
Better packaging
Increasing antisquat as body gets closer to axle, decreasing anti lift as they separate (Norm is this true for the S197 at all?) . . . sort of. It's detail-dependent. You can make the 3-link A-S decrease with squat and increase with rise just like a TA without having to try too hard. Actually, the OE 3-link A-L does increase with an increase in rear ride height, just that it's a pretty slow effect. See thumbnail (it's as close as measurements to within less than ±0.1" are worth).

3 Link Cons
Walking IC (potential for instability over bumps?)
Added bushings in shitty to replace locations
PITA to swap out
Huge increase in NVH? . . . detail-dependent
Technically binds in roll/competes with geo roll center unless spherical/spherical ended


Norm

Alright, if I am reading that chart correctly the OEM Antisquat value is around 32%? If Im lowered 1.75" then also according to that chart I am still around 32%. I wonder what the TA would have for an antisquat value at that same ride height and if it would even be beneficial for forward bite? Obviously I would have roll understeer in larger amounts from lowering.

From our over generalization and over simplification list it would appear that the bind free roll and the removal of a bushing are the two biggest pros. The roll freedom certainly would help the axle over uneven surfaces which I am sure leads to driver confidence. I forgot that there is the potential for power on understeer with a TA due to it trying to lift the front of the car some. I cant say I understand how big of an effect that is or if it even matters. How much force does the pinion gear trying to climb the ring gear translate into upward motion with a TA?

 

[Norm Peterson]

Alright, if I am reading that chart correctly the OEM Antisquat value is around 32%? If Im lowered 1.75" then also according to that chart I am still around 32%. I wonder what the TA would have for an antisquat value at that same ride height and if it would even be beneficial for forward bite? Obviously I would have roll understeer in larger amounts from lowering.

I haven't tried any TA conversions for the S197 chassis - no basis for the chassis side TA pickup point coordinates. But since the roll steer is defined by the LCAs and the PHB/WL, it wouldn't change just from swapping the UCA out for a TA.

FWIW, those curves are specifically for a car with OE-ish spring rates (600 lb/in total wheel rate) and a 185-ish driver.

I forgot that there is the potential for power on understeer with a TA due to it trying to lift the front of the car some. I cant say I understand how big of an effect that is or if it even matters. How much force does the pinion gear trying to climb the ring gear translate into upward motion with a TA?

For a TA, the upward load at the chassis side pickup can be taken as axle torque divided by the TA length (pickup X-coordinate minus axle X-coordinate). Note that axle torque here is subject to traction limitations and differential limited slip capability.

There is more to nose lift than that directly due to the upward TA load at the pickup.


Norm

 

[dontlifttoshift]

Norm, is there enough there to actually lift the front of the car?....more so than a well prepped 3 link?....or does it just plant the rear tires better?

 

[barbaro]

Based on my experience, there is no lift to the front of the car and the rear wheels do plant better. Additionally, having brought the car down from 135 to 60 in approximately 200 feet there was no wheel hop or brake hop on that or any other occasion. The pitch of the chassis, whether fore and aft or side to side is much more stable under acceleration or braking load. That is the most noticeable difference.

 

[neema]

TA Pros:
Fixed IC
Nearly bind free when built correctly
Fixed pinion angle
One less shitty to replace bushing in the suspension
"Easier to drive"

TA Cons
Potential for brake hop on hard braking
Reducing antisquat as axle and body get closer, invreasing anti lift as they separate (brake hop potential)
Added unsprung weight
Reduced ground clearance
Potential need for exhaust modifications

3 Link Pros
Simple antisquat tuning independent of roll steer
Less unsprung weight
Better packaging
Increasing antisquat as body gets closer to axle, decreasing anti lift as they separate (Norm is this true for the S197 at all?)

3 Link Cons
Walking IC (potential for instability over bumps?)
Added bushings in shitty to replace locations
PITA to swap out
Huge increase in NVH?

What else can you guys think of for each setup?

i have a question regarding the potential for axle hop/brake hop with a TA: if the TA isn't mounted rigidly on its front point (i.e. it can slide back and forth), doesn't that mean most of the brake hop issues are mitigated? If so, how can it be use functionally for it's benefits under acceleration?

Correct me if I'm wrong, but a TA like the Cortex unit can "slide" forward and backward in its front mount, and is rigidly mounted to the axle in the rear. Is this what "locks" the IC? Also, is the rate of forward/rearward movement of the TA dictated by the arc of the LCAs?

This is extremely interesting to me but I feel like I've jumped into an intermediate level class and need to catch up!

 

[barbaro]

i have a question regarding the potential for axle hop/brake hop with a TA: if the TA isn't mounted rigidly on its front point (i.e. it can slide back and forth), doesn't that mean most of the brake hop issues are mitigated? If so, how can it be use functionally for it's benefits under acceleration?

Correct me if I'm wrong, but a TA like the Cortex unit can "slide" forward and backward in its front mount, and is rigidly mounted to the axle in the rear. Is this what "locks" the IC? Also, is the rate of forward/rearward movement of the TA dictated by the arc of the LCAs?

This is extremely interesting to me but I feel like I've jumped into an intermediate level class and need to catch up!

The cortex unit does slide back and forth in the front mount as to what effect that might have an axle hop I don't know. I believe the length of the torque arm can contribute to axle hop and the geometry has to be right. But if it is, then there is none. With the Cortex there is no axle hop that I can tell and I have driven it under street and track condition.

 

[Sky Render]

The cortex unit does slide back and forth in the front mount as to what effect that might have an axle hop I don't know. I believe the length of the torque arm can contribute to axle hop and the geometry has to be right. But if it is, then there is none. With the Cortex there is no axle hop that I can tell and I have driven it under street and track condition.

Read that link I posted. I believe what you're referring to is known as "decoupling." The purpose of it is to eliminate brake hop.

Sent from my toilet using Tapatalk

 

[Whiskey11]

i have a question regarding the potential for axle hop/brake hop with a TA: if the TA isn't mounted rigidly on its front point (i.e. it can slide back and forth), doesn't that mean most of the brake hop issues are mitigated? If so, how can it be use functionally for it's benefits under acceleration?

Correct me if I'm wrong, but a TA like the Cortex unit can "slide" forward and backward in its front mount, and is rigidly mounted to the axle in the rear. Is this what "locks" the IC? Also, is the rate of forward/rearward movement of the TA dictated by the arc of the LCAs?

This is extremely interesting to me but I feel like I've jumped into an intermediate level class and need to catch up!

Brake hop on a torque arm is caused by geometry and not bushing materials. A short TA moves the instant center further rearward which increases antisquat but decreases antilift. When applying the brakes really hard with a shorter TA the way the forces work on the TA will actually lift the rear axle off the ground which causes brake hop. To remove the brake hop you have to have an arm sufficiently long to eliminate it or you decouple it which is a lot more technical and difficult.

The IC is locked vertically in side view to where the torque arm applies its force through the chassis and yes the lower control arms define how far fore and aft the TA plunges in that front bushing.

The TA itself is not a part of the suspension that moves the car. That job is now soley on the LCAs. The TA contributes to forward bite by translating the force of the pinion gear trying to climb the ring gear in the diff into a fixed point in front of the axle. Because it is pushing up on the chassis mounting point it must also be pshing down on the axle end which plants the rear tires. Also as Norm pointed out, the TA is free to roll without bind which helps keep the axle on the pavement.

Norm, feel free to correct as necessary. I really need to buy the Mathis and Smith books.

 

[Norm Peterson]

The quick one is that the SVIC is not locked vertically with a TA. It's a picky little geometric construction involving the LCA side view inclination and a construction line drawn perpendicular to the axis of the TA (taken from the axle centerline to the chassis pickup point of vertical-ish constraint - "ish" because the TA axis does not have to be perfectly horizontal (and frequently isn't).

So as the LCA inclination varies (with ride height), so does the SVIC, and that's how the anti-squat varies.


Norm

 

[Whiskey11]

The quick one is that the SVIC is not locked vertically with a TA. It's a picky little geometric construction involving the LCA side view inclination and a construction line drawn perpendicular to the axis of the TA (taken from the axle centerline to the chassis pickup point of vertical-ish constraint - "ish" because the TA axis does not have to be perfectly horizontal (and frequently isn't).

So as the LCA inclination varies (with ride height), so does the SVIC, and that's how the anti-squat varies.


Norm

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?

Norm, tonight I'm going to put my car up and get a measurement from the driveshaft central bearing to the end of the diff to get you a very rough TA length that the Cortex unit is since that is where theirs mounts to. I would also like to find out the angles of my LCA's are since I'm sure that figure will also be important.

I'm also going to PM you about making an ST/SP compliant LCA "bushings" if you don't mind. I think these "bushings" are going to be necessary for use with a TA to keep the rear end properly centered.