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Old 07-23-2021, 03:06 PM   #1
Paul_E_D
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Default chassis bracing 101?

I have searched, but could not find a thread that explains what braces to use for what applications. I have an 18STi that sees occasional track use and I feel like it could benefit from some bracing. The back end feels pretty vague under hard braking at high speeds and in direction changes. And of course, it suffers from understeer.

I just installed a cusco x brace and perrin strut tower brace, but I see sooooo many braces out there. Not sure if I went the right direction.
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Old 07-23-2021, 03:33 PM   #2
murrdogg24
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I think you're wanna do suspension modifications to get rid of the understeer, bracing will not solve that issue. I can tell you how I did it on my GD, replace all the bushings with pillowball, upgrade sway bars, whiteline alk and RCA kits. Then get a performance alignment, not stock specs. Once you've done all that then get some bracing.
Quote:
Originally Posted by Paul_E_D View Post
I have searched, but could not find a thread that explains what braces to use for what applications. I have an 18STi that sees occasional track use and I feel like it could benefit from some bracing. The back end feels pretty vague under hard braking at high speeds and in direction changes. And of course, it suffers from understeer.

I just installed a cusco x brace and perrin strut tower brace, but I see sooooo many braces out there. Not sure if I went the right direction.
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Old 07-24-2021, 11:42 AM   #3
Paul_E_D
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Well, I took the car for a few good rips. I don't think I was wrong. It feels tighter and more composed when pushing the pace. It does seem to corner flatter and feels a bit racier. What really surprised me is how much better it feels on rough surfaces.

Murrdogg, I'm sure you are correct about setting the car up to reduce understeer. Care to share more detail about your settings? I want it to remain a decent daily driver, but getting the pivot point further back would be most satisfying.
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Old 07-26-2021, 11:27 AM   #4
BlackFighter
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Not sure about the newer years but the strut tower brace was useless for the earlier years like the GD. Good shocks, springs, tops hats, bushing upgrades is a good start. Ow and good tires help more then people think.
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Old 07-27-2021, 08:28 AM   #5
Norm Peterson
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Quote:
Originally Posted by Paul_E_D View Post
Well, I took the car for a few good rips. I don't think I was wrong. It feels tighter and more composed when pushing the pace. It does seem to corner flatter and feels a bit racier. What really surprised me is how much better it feels on rough surfaces.
Supplemental bracing does more for driver confidence than it does for actually improving measured performance. Cars these days are stiff enough, particularly in overall torsion, such that adding small-dimension tubing can't increase that by very much. Or actually flatten the cornering rather than just some perception that it might have.

Don't overlook the importance of driver confidence here. Driving and handling are still partly about the car and partly about its driver. Just don't expect miraculous numerical improvements once the driver has upped his skill levels.


Norm
(retired structural engineer, life-long corner-carver)
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Old 07-28-2021, 08:58 AM   #6
BlueSTI4Me
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Come on over to Track Subies - Group on the book of faces plenty of VA HPDE owners and Time Attack owners that can help with VA setup.
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Old 07-28-2021, 02:22 PM   #7
Paul_E_D
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Originally Posted by BlueSTI4Me View Post
Come on over to Track Subies - Group on the book of faces plenty of VA HPDE owners and Time Attack owners that can help with VA setup.
Thanks. I joined. Definitely more info there. Seems geared towards heavily modified cars, but helpful nonetheless
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Old 07-29-2021, 09:07 AM   #8
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Quote:
Originally Posted by Norm Peterson View Post
Supplemental bracing does more for driver confidence than it does for actually improving measured performance. Cars these days are stiff enough, particularly in overall torsion, such that adding small-dimension tubing can't increase that by very much. Or actually flatten the cornering rather than just some perception that it might have.

Don't overlook the importance of driver confidence here. Driving and handling are still partly about the car and partly about its driver. Just don't expect miraculous numerical improvements once the driver has upped his skill levels.


Norm
(retired structural engineer, life-long corner-carver)
I'll be curious to see if there are any measurable gains with the cusco X-brace. I will say that the car feels different. It's not in my head. However, I'm not sure I have the patience to hold off on a 24mm rear bar before my next track day.
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Old 07-29-2021, 09:21 AM   #9
Norm Peterson
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Quote:
Originally Posted by Paul_E_D View Post
I'll be curious to see if there are any measurable gains with the cusco X-brace. I will say that the car feels different. It's not in my head. However, I'm not sure I have the patience to hold off on a 24mm rear bar before my next track day.
The hard part is going to be separating the effects of improved driver confidence from any actual measurable gains. Test drivers get paid big bucks for their ability to do that. The rest of us?


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Old 07-29-2021, 09:34 AM   #10
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Here's a link to a thread with a video on the rear strut tower x-brace on a GD chassis. It definitely stiffens up the rear as shown in the video with how much movement with it disconnected. This video convinced me to grab one for my bugeye. Not sure how much of this would translate to the newer chassis though.

https://www.iwsti.com/threads/does-a...e-work.202634/
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Old 07-29-2021, 09:32 PM   #11
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Quote:
Originally Posted by Norm Peterson View Post
The hard part is going to be separating the effects of improved driver confidence from any actual measurable gains. Test drivers get paid big bucks for their ability to do that. The rest of us?


Norm
I mean, confidence is everything, I agree (I'm a successful expert roadracer on motorcycles), but set up breeds confidence, so doesn't that make the bracing worth it?

The car flexes a lot more without it. If the bolts on the brace are a little loose you can hear the car flex almost immediately on turning. I feel like the suspension is working better with the brace.

I'm excited to try it out at Palmer in october.
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Old 07-29-2021, 10:58 PM   #12
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Ya I got a Kein X-brace sitting in the garage. Waiting till the weather gets a little cooler to install it.
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Old 07-30-2021, 08:54 AM   #13
Norm Peterson
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Quote:
Originally Posted by Paul_E_D View Post
I mean, confidence is everything, I agree (I'm a successful expert roadracer on motorcycles), but set up breeds confidence, so doesn't that make the bracing worth it?
Of course it does. And that's where I'm saying most of the benefit lies. A lot of this is subjective perceptions regarding vibrations and structural modeshapes.

Structurally unless your car is a wet noodle to begin with, adding small amounts of torsional stiffness over only part of the car's wheelbase isn't going to do much at all.

If such bracing locates the wheels more rigidly relative to the chassis (which I think you should be able to feel), that'd be by far the more important actual performance benefit.


Quote:
The car flexes a lot more without it. If the bolts on the brace are a little loose you can hear the car flex almost immediately on turning. I feel like the suspension is working better with the brace.
It doesn't take much relative movement in insufficiently tightened connections for noises to result . . . half a mm would be plenty, and that is simply lost in comparison to the inch or more of lateral tire distortion at the contact patch.


I find most videos feature a person who likes to put his face on the camera and blather on endlessly, so I don't normally watch them. I'll have to make an exception here to see what "flexing" is being referred to and hope that I'm not trying to pick out 10 seconds of useful information out of 10 minutes of clutter. Offhand, I suspect that the flexing is mostly lateral in nature.



Quote:
I'm excited to try it out at Palmer in october.
consider this a virtual thumbs-up smiley. NASIOC smiley list doesn't include a "real" one . . .


Norm

Last edited by Norm Peterson; 07-30-2021 at 09:09 AM.
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Old 07-30-2021, 09:27 AM   #14
Norm Peterson
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OK, having watched the video it's not the same kind of bracing that comes up when I searched for Cusco Subaru X brace.

Yeah, when the roof structure isn't adequately tied to the platform you're going to get a lot of lateral flex between the two structures, roof relative to platform, And the platform now being forced to carry most of the torsional loading is also going to exhibit greater deflections.


Idle thought . . . I wonder if adding the bracing shown in the video has resulted in an increased frequency of windshield or A-pillar cracking. When you force more load to go through the roof structure, the entire roof structure including its pillars have to be carrying it as well. Roof deflections up front would tend to increase.


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Old 07-30-2021, 11:02 AM   #15
BlackFighter
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People have been using the X-Braces for the GD for years and no issues reported. But I understand what you mean.
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Old 07-30-2021, 11:09 AM   #16
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Quote:
Originally Posted by Norm Peterson View Post
OK, having watched the video it's not the same kind of bracing that comes up when I searched for Cusco Subaru X brace.

Yeah, when the roof structure isn't adequately tied to the platform you're going to get a lot of lateral flex between the two structures, roof relative to platform, And the platform now being forced to carry most of the torsional loading is also going to exhibit greater deflections.


Idle thought . . . I wonder if adding the bracing shown in the video has resulted in an increased frequency of windshield or A-pillar cracking. When you force more load to go through the roof structure, the entire roof structure including its pillars have to be carrying it as well. Roof deflections up front would tend to increase.


Norm
I've been running an x-brace for ~6 years with no noticeable issues. I've heard about, but not experienced, people having issues with some of the tack welds around the strut tower area breaking free from the added loading. I'd consider that more anecdotal than data, though.
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