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LCA Relocation Brackets...

I am looking at LCA brackets as a cheap and easy piece to try on my car, but looking for some real-world feedback first to see if they are worthwhile.

Context: 2011 Mustang GT autocross car, setup for SCCA CAM-C. BMR handling springs (~1.5-2" drop), Koni yellows, MM C/C plates, adjustable Panhard, BMR 38mm front / Strano 25mm rear bars, 285/35 RE71's on 19x10.5 square.

Behavior: The car is a little pushy, until coaxed into throttle oversteer. When it transitions to oversteer, the yaw rate is pretty high (tail comes out fast). In current form, the LCA's are higher at the axle and by about 1-1/4".

I understand anti-squat and roll steer, and can easily envision what these LCA angles should do to dynamics, but...

Anyone have back-to-back with and without experience?

Is the impact noticable / significant for an autox car?

Do they impact steady-state corner balance?

How do they impact balance accelerating off of corners?
 
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Good point...I was thinking in relation to the LCA inclination only. I need to spend more time under the car thinking to envision the Panhard impacts, but open to thoughts/suggestions/experience all the same.
 

Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
Good point...I was thinking in relation to the LCA inclination only. I need to spend more time under the car thinking to envision the Panhard impacts, but open to thoughts/suggestions/experience all the same.
Here's the usual 3-link/PHB roll steer sketch. For the S197 the LCAs commonly converge to the rear in plan view, but that's the only difference. The slope of line A-B is the % roll steer.

3-link roll steer.jpg


For a slight amount of roll understeer, you actually would want the axle-side pivots of the LCAs to be higher than the chassis-side pivots in order to have the LCA convergence point lie above and behind the mid-height of the PHB. Somewhere around 2% - 4% roll understeer seems to be a good place for this to be.


Norm
 

302 Hi Pro

Boss 302 - Racing Legend to Modern Muscle Car
2,009
438
Southeast
Hi S9669’s:

Interesting questions and rest assured that you are chatting with 2 of the best Forum Members to answer your technical S197 rear suspension questions.

I’m not a suspension Engineer by any stretch so my approach was to copy the suspension setups of those who were winning Championships with S197 Mustangs.

Back in the day (2011/12), when I looked to rebuild my 2012 Boss 302 rear suspension to eliminate rear axle/wheel hopp & to help manage the oversteer rear live axle swing, I looked at setups from the Ford Racing/MultiMatic Boss 302R Race Program, (circa 2010), Tiger Racing/Paul Brown’s Triple Crown Championship Boss 302 #50 Mustang, (circa 2011/12) & lastly for the S197 chassis, the Cortex Racing Mustangs of the 2013/14 circa.

The latter 2 teams were winning a lot of races back in the day. Hope this info helps you a bit as you ponder your 2011 S197 rear suspension set up.
 
Grant, thanks for catching my error...axle end is ~1-1/4" higher (not 1/4"). That said, I am measuring with sub-optimal tools and access, so I'd put a ~1/4" error band on that that. My Panhard is really close to level - very slightly higher on the chassis (passenger) side if that helps frame it better.

Norm, thanks for the diagram. I'll need to spend more time measuring to see where I am on roll steer now.


Thoughts from either of you (or others) on the impact of lowering the LCA connection point on the axle based on the above? I am looking for more nimble, and more progressive breakaway and recovery, which I think in theory supports using brackets, but I am coming back to...

1. Is it significant/noticable?
2. Are there impacts on steady-state cornering or other aspects I should be aware of before trying it?
 
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Grant 302

basic and well known psychic
Interesting questions and rest assured that you are chatting with 2 of the best Forum Members to answer your technical S197 rear suspension questions.

302 Hi Pro, Thanks - this is exactly why I am here.

Thanks to you both for the kind comments. But honestly, I’d never want comments including or about me to discourage anyone from joining technical discussions in this forum.

s9669s - I’m glad you posted this question in the forum and I hope you understand why I asked you to do so when you PMd me.

Thanks for checking the measurement/typo and I’ll get back to some of your questions when it’s a bit quieter in the house.
 
s9669s,

Disclaimer: not a track rat or dragstripper.

LCA brackets will certainly greatly reduce wheel hop. P springs dropped the rear by about 1" (not drastic at all) but the LCAs pointed down (back-to-front) and wheel hop was quite bad on wet roads and cool ambient temperatures (Fall weather). Installed the brackets and used the center hole as a starting point. The LCAs now point up a little bit (3/4 to 1" lower at the back connection relative to the torque box connection) and wheel hop is gone. Significant improvement, imo.

For autocrossing, the bracket vendor (BMR) recommended the top hole [for a 1" drop] to make the LCAs almost parallel or, maybe, even pointing down a bit (back-to-front). Mr. Peterson (or 302 Hi Pro) can easily explain the dynamics but having an extreme angle (rising from the axle connection to the body connection) is great for the dragstrip (straight line stuff) but, on a road course, that angle can result in unexpected snap oversteer.

That's the sum total of my experience with LCA brackets,

HTH,

Chris
 
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Grant 302

basic and well known psychic
Anyone have back-to-back with and without experience?
Yes - When I first tried brackets, I did it as a single mod/change. I also drive two cars back to back, geometry-wise the fronts are similar and the main difference in the back are brackets and ride height.

Is the impact noticable / significant for an autox car?
Yes, I think so. Low speed corners show differences in roll steer and anti-squat pretty readily, IMO.

Do they impact steady-state corner balance?
I think so...and toward oversteer.

How do they impact balance accelerating off of corners?
There’s a bit of give and take regarding acceleration. Generally, I think a car that squats ‘needs’ smoother application of power and to be applied while there is lateral weight transfer to the outside wheel. With brackets, and more dynamic anti-squat, throttle application can be much sharper/faster like stabbing the pedal. Downside is that the anti-squat reduces the max throttle input.

I believe this is where many would argue otherwise...because of the increased anti-squat. Most think this alone means greater ability to put power down. Less power, but faster transition is possible.


1. Is it significant/noticeable?
Yes. Most brackets have a first adjustment point of 2” lower, and 1” more for each additional hole. Geometry wise these are all big jumps, IMO.

2. Are there impacts on steady-state cornering or other aspects I should be aware of?
Changes in roll steer are not necessarily confidence inspiring and may require adjustments in driving style.
 
Chris and Grant, thanks...this is helpful.

I think the impact on steady-state cornering (toward oversteer) should make the car slalom faster (if a bit more nervous), which will help for the slalom-intensive courses I see locally.

Regarding acceleration off the corner, do you have a feel for how the brackets impact oversteer (yaw rate) after breaking the tires loose? Right now, it feels like my car wants to come around quickly when the tires let go. Taming that a bit will make steering with the throttle more manageable... (This may also be a function of tires--RE71's don't seem to like much slip angle.)

Lower forward thrust capacity while turning sounds like the downside...getting back on the power early is one of the keys to maximizing these cars' strengths.
 

Grant 302

basic and well known psychic
Chris and Grant, thanks...this is helpful.
Glad to help. I forgot to ask: Are you using the stock trailing arms? The stock ones don’t fit in all brackets due to their size at the ends to fit the big bushings. FP brackets need aftermarket arms.

I think the impact on steady-state cornering (toward oversteer) should make the car slalom faster (if a bit more nervous), which will help for the slalom-intensive courses I see locally.
I think that’s correct.

Regarding acceleration off the corner, do you have a feel for how the brackets impact oversteer (yaw rate) after breaking the tires loose? Right now, it feels like my car wants to come around quickly when the tires let go. Taming that a bit will make steering with the throttle more manageable... (This may also be a function of tires--RE71's don't seem to like much slip angle.)
This sounds right to me. But the most I lowered the car without brackets was 1” with P springs, and 1/2” before that with the 55D springs. I have experience with RE-11s, but on an AWD car.

Lower forward thrust capacity while turning sounds like the downside...getting back on the power early is one of the keys to maximizing these cars' strengths.
Considering how much your car is lowered, you might not even have or feel any adverse effects in this regard with a 2” adjustment on the bracket. If enough ‘dynamic squat’ and related weight transfer is (still) generated on the outside tire.
 

Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
Yes, I think so. Low speed corners show differences in roll steer and anti-squat pretty readily, IMO.
Noticeable, yes. With my experience coming from a somewhat different direction, a small amount of roll steer in the vehicle understeer direction (2.5% - 3%) is considerably more nimble than greater amounts (say, 10% or so). Seems to be most noticeable in slalom maneuvers.


I think so...and toward oversteer.
Agreed. Vehicle-oversteerish axle steer behaves like extra rear slip angle, except that it's based on the amount of roll rather than the actual vertical tire loads. Related effects, but not necessarily in lock-step with each other.


There’s a bit of give and take regarding acceleration. Generally, I think a car that squats ‘needs’ smoother application of power and to be applied while there is lateral weight transfer to the outside wheel. With brackets, and more dynamic anti-squat, throttle application can be much sharper/faster like stabbing the pedal. Downside is that the anti-squat reduces the max throttle input.

I believe this is where many would argue otherwise...because of the increased anti-squat. Most think this alone means greater ability to put power down. Less power, but faster transition is possible.
I think so. With less anti-squat, it's more on the driver to not feed power in so fast that rear suspension squatting (rear spring compression and elastic load transfer) can't keep up. Tires can be loaded much more rapidly with power when more of the rearward load transfer is coming through the geometry, which happens much more quickly than elastic load transfer (which also includes dynamically through the shocks while the suspension is actually in the process of squatting).


Most brackets have a first adjustment point of 2” lower, and 1” more for each additional hole. Geometry wise these are all big jumps, IMO.
This ^^^

Only a quarter inch difference in LCA relocation at the axle is worth something like a 1.5% change in axle roll steer. If your axle steer is in the 2.5% vehicle understeerish range as it is, a half inch downward change at the relo brackets would nudge you over into having a tiny bit of oversteerish axle steer. Not undriveable, but noticeably looser.


Changes in roll steer are not necessarily confidence inspiring and may require adjustments in driving style.
For sure. And what may be useful amount of loose roll steer on an autocross course laid out for Miatas, Minis, and S2000's might be unnerving in a high speed sweeper on a big track.


Norm
 

Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
Chris and Grant, thanks...this is helpful.

I think the impact on steady-state cornering (toward oversteer) should make the car slalom faster (if a bit more nervous), which will help for the slalom-intensive courses I see locally.

Regarding acceleration off the corner, do you have a feel for how the brackets impact oversteer (yaw rate) after breaking the tires loose? Right now, it feels like my car wants to come around quickly when the tires let go. Taming that a bit will make steering with the throttle more manageable... (This may also be a function of tires--RE71's don't seem to like much slip angle.)
Might have to reconstruct the car's original condition, or I might have to try to find my car's original measurements. The point being to try to establish where your car is now compared to OE.

I do know that a minimal amount of lowering on my car - a little over half an inch all around and without doing any LCA relocating - seems to have taken away a useful amount of lift-throttle turn-in. Which says pushy rather than loose. More LCA relocating than lowering suggests looser and less resistance to yaw developing.


Norm
 
I am still on OE LCA's--car has under 30k miles, and they seem to be in good shape, but open to thoughts.

It seems like I ought to acquire a set of brackets to see how they feel. In theory, I think roll steer should make the car feel more nimble as the axle will help steer the the rear of the car. I think it should also make oversteer more tractable as it decreases slip angle.

In terms of brackets, I would prefer something adjustable and bolt-on. BMR has three holes, but again, open to suggestions--I think I read stock arms don't fit in the top holes on them, but they do in the lower holes.
 
3,777
3,710
LCA = trailing arms
trailing arms run north and south, control arms run east and west

Also I think Phoenix Performance may still have a dozen or so of those trailing arm mounts lying around that they didn't use, prolly get them cheap.
 
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Grant 302

basic and well known psychic
In terms of brackets, I would prefer something adjustable and bolt-on. BMR has three holes, but again, open to suggestions--I think I read stock arms don't fit in the top holes on them, but they do in the lower holes.
Best to check with them directly. A long time ago I was told that FRPP brackets fit the stock arms...nope. Found that one out the hard way.

the other guy..lol

I know, but we can only do so much, right? 🤔 :)
 

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