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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Rear Sway Bar for Track Car



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      09-26-2018, 10:23 AM   #23
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Originally Posted by cvc 22349a View Post
M3 F/R sway bars imo. Been a long time since I looked at this stuff but that seemed to be the best combo a few years ago, iirc that H&R rear bar is solid v. M3 is hollow.
I agree with this. I've tried dozens of combos. Like you said, you cannot compare aftermarket bars to stock sway by diameter because the stock bars are hollow and have more BENDS in them as well. Aftermarket sway bars like H&R are actually pretty stiff. Much more so then M3 bars.

The M3 bars are well balanced F:R and they are also more mild upgrades over stock which pair well with mild spring upgrades.

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Originally Posted by rismo View Post
I have a similar setup and also not happy with my car handling.

- Full m3 stuff, Drexler LSD, suspension/engine "mounts" replaced with medium hard rubber versions
- M-sport sway in the front
- M3 sway in the back

My issue: I lose traction halfway the corner on my outer rear wheel. This is caused due to the to stiff rear m3 sway bar.
We don't know your spring rates so it's hard to speculate on your issue. But, I would have to disagree with you based on the information that you've provided.

Most cars already have front m-sport sway bars in stock trim. The E92 M3 front bar is stiffer than the M-sport bar and will better match the rear M3 bar you've installed.

I actually ran the same sway bar setup as you for a while (stock M-sport bar front and M3 bar rear). I did this because the stock 15mm sway bar is useless and the car under-steered pretty badly. The car actually felt pretty well balanced with the rear M3 bar but slightly over-steer oriented. I pulled my fenders and put on a set of low offset wheels in the rear to better match eh very aggressive front wheel fitment I had. That made a massive difference in keeping the rear stable. You don't mention your wheel setup or spring setup.

I recently upped my front bar to an M3 sway bar and the car feels perfectly balanced now. The car does not pitch forward as much during roll and the rear tires stay on the ground better.

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Originally Posted by rismo View Post
My plan:
- Chamber plates in the front (More negative chamber)
- Linear spring around and in the rear also stiffer springs
- Replace the rear sway with a normal m- sport sway

With replacing the rear sway back to original I hope to achieve 2 things:
- Bring the car back in balance
- Allow the rear wheels to move more independent
I think you'll be wasting your time with these proposed changes. Sounds like a lot of work for little change. While stiff springs and small sways is a very common suspension theory setup, I don't see how your changes are directed at fixing your issue. Rather, they completely change the theory behind your suspension setup instead of making your current setup work better.

- Front camber is not going to help the rear lifting tires.
- Stiffer springs are not going to help the rear lifting tires even though this WILL be necessary if you take the sways out.
- Replacing the rear M3 sway with the stock sway in theory WILL help your issue, but, the issue isn't that the M3 bar is too stiff causing the tires to pull off the ground. The issue sounds more like your need to upgrade the FRONT sway to better match the rear and prevent forward pitch in roll.

Quote:
Originally Posted by AWDBooSTIn90 View Post
The Msport Front Sway bar also tapers like the 335 front sway bar does also I believe. Why not try a stock M3 front sway bar? Then you can decide if you want to remove the M3 rear sway bar.
Going from the 335i RSB to the M3 RSB is a big jump in stiffness.
@rismo This sounds to me like the least amount of work to make your setup work for you.

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Originally Posted by AWDBooSTIn90 View Post
Ive personally liked the M3 FSB & stock RSB combo I am currently running. I dont know if I would change to an M3 RSB without trying out stiffer rear springs first. The back end seems to come out when I want it too, under heavy steering and then applying a decent amount of power. Plus the car barely understeers with the M3 front control arms and M3 FSB.
This sounds more like you're compensating for the lack of rear roll resistance and by capitalizing on the advantages of RWD (power oversteer) to ge tthe car to rotate how you want it to. M3 front sway and and 15mm stock sway under-steered pretty badly on my car, but, I also don't know your spring rates, wheels, bump stop, and other mods to actually make it a fair comparison.

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Originally Posted by rismo View Post
I was actually thinking about the same, however I want to understand why BMW does not apply that ratio themselves and went for a heavy rear sway and springs.
Not sure what you mean here... You are looking at it the wrong way I think. A base model car was not delivered with a neutral handling suspension. It was delivered to under-steer. BMW gave a stock car a very small rear sway bar and a staggered wheel/tire setup.

BMW delivered the M3 with a beefier rear bar because the stock car doesn't even come with one in many instances lol not because they messed up the "ratio."

Also, the M3 has a slightly different suspension geometry, so, the spring rates will not follow the same exact ratio as a stock car.
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      09-26-2018, 11:34 AM   #24
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bbnks2 the difference is that you have 1-series which is more nervous that 3-series so what works on your 1-series, or it didn't, won't translate directly as a rule for the 3-series. M-Sport in EU is different than M-Sport in USA that give you just an appearance package and I think M-Sport in EU utilizes the swaybars from the BMW Performance kit sold in USA https://www.ecstuning.com/b-genuine-...iABEgII1fD_BwE Also, the base 3-series isn't 335i nor 328i. It's 316i, 4cyl, with sqaure setup that has neutral handling. Yes, M3 has slightly different suspension geometry and accidentally installing m3 rear swaybar make your 1-series and someone else 3-series to handle better considering the other changes you had made already. However, there is a reason why BMW in the Performance kit left out the rear swaybar. The front Performance swaybar is same size as the m3 I believe.Other manufactures and tuners are doing and have done the same. What is your opinion on my question that if the vehicle is easier to rotate because is tail happier will that translate into faster speed throughout the turn?
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      09-26-2018, 12:21 PM   #25
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Originally Posted by feuer View Post
bbnks2 the difference is that you have 1-series which is more nervous that 3-series so what works on your 1-series, or it didn't, won't translate directly as a rule for the 3-series. M-Sport in EU is different than M-Sport in USA that give you just an appearance package and I think M-Sport in EU utilizes the swaybars from the BMW Performance kit sold in USA https://www.ecstuning.com/b-genuine-...iABEgII1fD_BwE Also, the base 3-series isn't 335i nor 328i. It's 316i, 4cyl, with sqaure setup that has neutral handling. Yes, M3 has slightly different suspension geometry and accidentally installing m3 rear swaybar make your 1-series and someone else 3-series to handle better considering the other changes you had made already. However, there is a reason why BMW in the Performance kit left out the rear swaybar. The front Performance swaybar is same size as the m3 I believe.
The wheelbase is a hair shorter on the 1-series compared to the 3-series, yes, but these cars are essentially the same in regard to suspension tuning.

I am not sure what you mean when you talk about EU cars... The packages each car comes with varies and so do the sway bars they come with, but, the sway bars themselves are no different than the EU sways. None of them are as stiff as the M3 bars. They all taper in the middle and none of them have the bushing stoppers or the stiffer bushings like the M3 bars have. My point was that an MSport sway is not as stiff as an E92 M3 sway. Not sure what point you're trying to make in regard to this.

Also, Msport in the USA is just an appearance package because a "sport package" is offered as a separate option. The sport package (which comes with Msport sways) is actually a standard option on a car like the N55 135i. If I were to buy the BMW performance sway bar, it would be the same damn thing my car already has. I know this because I have held both bars in my hands. I do there are some slight difference though like some people like myself have reported their bushings were fixed to the sway.

The BMW performance package was put together by BMW for 3-series cars, specifically. Many of these cars did not come with the "sport suspension" option. I think the simple reality of the BWM performance suspension is that it doesn't include a rear sway because it's not likely that anyone is going to drop the sub-frame to install one. That results in massive effort on the dealers part to install it if they want to sell cars with this package. It also deters potential customers from buying the performance package when they hear they need to drop another $2k into labor for the install. I don't think it has anything to do with keeping the handling neutral. I don't think it has anything to do with the 3-series being different than the 1-series so much so that it requires no rear bar to be neutral. That is just not how roll couple works.

I think the major factor in the lack of a rear bar on NON-M cars is to help prevent soccer moms from accidentally drifting their RWD coupe into a light-pole. BMW has to make the car easy to drive for teh masses. under-steer is safe. A 335 or a 135i is a "sporty" luxury commuter car not a "sports car." Big difference and market there. Sport cars are for the M division.

Quote:
Originally Posted by feuer View Post
other manufactures and tuners are doing and have done the same. What is your opinion on my question that if the vehicle is easier to rotate because is tail happier will that translate into faster speed throughout the turn?
I never replied to the OP or his situation. I only replied to other people who are misrepresenting Orbs's data and inferring it means something it doesn't.

In regard to your question, I would typically agree that making the rear of the car stiffer should be thought of as increasing over-steer rather then decreasing under-steer. I think OP needs to post up more relevant info like wheels sizes and offsets as well as spring rates and strut design (bump stops) to determine what he might need to address to reduce under-steer. He could try removing his front bar to match his non-existent rear bar. That worked for me when I tried it, but, the car was then TOO SOFT overall and had too much roll given the relatively modest spring rates I run.
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      09-26-2018, 02:03 PM   #26
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Quote:
Originally Posted by bbnks2 View Post
The wheelbase is a hair shorter on the 1-series compared to the 3-series, yes, but these cars are essentially the same in regard to suspension tuning.

I am not sure what you mean when you talk about EU cars... The packages each car comes with varies and so do the sway bars they come with, but, the sway bars themselves are no different than the EU sways.


None of them are as stiff as the M3 bars. They all taper in the middle and none of them have the bushing stoppers or the stiffer bushings like the M3 bars have. My point was that an MSport sway is not as stiff as an E92 M3 sway. Not sure what point you're trying to make in regard to this.
There are some more differences between the both packages (EU vs US). EU is slightly more aggresive, however that is not your point, your point is that the chassis can have a firmer sway configuration and that non-m packages are all soccer-mom friendly designed.

Based on the rate numbers of the M and the Non-M configs that could be a fair explanation. As the M has stiffer springs plus stiffers sways. Also the F/R ratio is significant more aggresive on the M.

Regarding the 1 series and 3 series, there is quite some difference in the dynamics between both. And not every suspension part can be exchanged (Brakes, certian bolts and links etc).

Anyway will dig into your sugestion, thanks, but the last thing I wanted to do is kill Vassilovs thread. So please let's focus on his challenge. I will open a new thread when updates arrive .
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      09-26-2018, 11:02 PM   #27
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Quote:
Originally Posted by feuer View Post
bbnks2 the difference is that you have 1-series which is more nervous that 3-series so what works on your 1-series, or it didn't, won't translate directly as a rule for the 3-series. M-Sport in EU is different than M-Sport in USA that give you just an appearance package and I think M-Sport in EU utilizes the swaybars from the BMW Performance kit sold in USA https://www.ecstuning.com/b-genuine-...iABEgII1fD_BwE Also, the base 3-series isn't 335i nor 328i. It's 316i, 4cyl, with sqaure setup that has neutral handling. Yes, M3 has slightly different suspension geometry and accidentally installing m3 rear swaybar make your 1-series and someone else 3-series to handle better considering the other changes you had made already. However, there is a reason why BMW in the Performance kit left out the rear swaybar. The front Performance swaybar is same size as the m3 I believe.Other manufactures and tuners are doing and have done the same. What is your opinion on my question that if the vehicle is easier to rotate because is tail happier will that translate into faster speed throughout the turn?
Not quite, the performance suspension front sway bar still has the center tapered section as the sport suspension bar but has additional curvature/kinks towards the ends of the bar. No idea what that does. I have that bar and feel no difference between it and the sports suspension bar.
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      09-27-2018, 08:27 AM   #28
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Quote:
Originally Posted by cvc 22349a View Post
Not quite, the performance suspension front sway bar still has the center tapered section as the sport suspension bar but has additional curvature/kinks towards the ends of the bar. No idea what that does. I have that bar and feel no difference between it and the sports suspension bar.
Usually more kinks make a sway bar LESS effective. Maybe that's what BMW does with the BMW Performance sway bar... They REDUCE the front sway rate to better match the non-existent rear sway in the cars it was designed for lol

Msport and BMW Performance sway are a bit different, yes, the point was that neither is as stiff as an M3 bar. The BMW perofrmance sway has the same diameter and taper as the Msport sway. The BMW performance sway just has some extra kinks in it as you pointed out.
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      09-27-2018, 09:53 AM   #29
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Quote:
Originally Posted by cvc 22349a View Post
Not quite, the performance suspension front sway bar still has the center tapered section as the sport suspension bar but has additional curvature/kinks towards the ends of the bar. No idea what that does. I have that bar and feel no difference between it and the sports suspension bar.
Quote:
Originally Posted by bbnks2 View Post
Usually more kinks make a sway bar LESS effective. Maybe that's what BMW does with the BMW Performance sway bar... They REDUCE the front sway rate to better match the non-existent rear sway in the cars it was designed for lol
Why is that more bends in the swaybar would make it less effective?
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      09-27-2018, 10:50 AM   #30
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Why is that more bends in the swaybar would make it less effective?
I have no idea about the effect, simply stating it is a different shape than the oe sport suspension front bar. I'd actually like to know what these additional kinks do as that bar is on my car.
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      09-27-2018, 02:15 PM   #31
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Originally Posted by feuer View Post
Why is that more bends in the swaybar would make it less effective?
From what I understand, by adding bends, applied force is translated into bending force and reduced the amount of force that is applied to the straight section of the sway bar which is mounted to the chassis and provides the torsional stiffness.

Same concept as ensuring the sway bar tabs are adjusted to be parallel to the ground with the car at ride height... If you adjust your end-links incorrectly, and position the sway bar tabs incorrectly, the sway bar won't be leveraged the same as if the tabs were parallel to the ground/mounting brackets/chassis. The end-link mounts should also line up in a vertical plane (usually not possible). You reduce the effectiveness of the sway bar with increasing angle on the end-links. It's not uncommon for people to weld new tabs on to their struts to correct the end-link alignment after making lots of suspension changes. This is why simple things like ride height changes can have a huge impact on suspension tuning discussion.

Here is a technical article that shows how the transition from bending force at the sway bar arms is gradually transferred to torsional resistance through the straight section of the sway bar: http://delibra.bg.polsl.pl/Content/2...-Part_0000.pdf

Here is a less technical article that states in plain English instead of math: http://speed.academy/how-swaybars-work/2/

Quote:
a bar with a lot of bends needs to use a larger diameter to achieve the same spring rate as a straight bar...
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      09-27-2018, 02:17 PM   #32
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Quote:
Originally Posted by cvc 22349a View Post
I have no idea about the effect, simply stating it is a different shape than the oe sport suspension front bar. I'd actually like to know what these additional kinks do as that bar is on my car.
Yes, thanks for correcting me. There is definitely minute differences in all of those sway bars. I called them all the same because I meant that none of them vary by anything as significantly different as jumping up to M3 sways (which still aren't that stiff compared to aftermarket). If you put an M3 rear sway in your car then an Msport sway is not going to balanced with it.

I remember this coming up in another thread too and the extra bends in the BMW performance bar were mentioned. Definitely looks like BMW is reducing it's effectiveness to me but I'd love for someone else to chime in.
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      09-27-2018, 11:06 PM   #33
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Let me try this one more time.

My coilovers are with linear springs. 450lb on the front, 700 in the rear.

Why do we keep talking about stock 335i spring rates in relationship to my question?

So the consensus here is that the M3 RSB will be too stiff in combination with 335i FSB, correct?
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      09-27-2018, 11:58 PM   #34
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Quote:
Originally Posted by vasillalov View Post
Let me try this one more time.

My coilovers are with linear springs. 450lb on the front, 700 in the rear.

Why do we keep talking about stock 335i spring rates in relationship to my question?

So the consensus here is that the M3 RSB will be too stiff in combination with 335i FSB, correct?
I wish I remembered the guy's name on this forum a few years ago, good guy who had an E92 with JRZ suspension, track car, 600#F, 700#R and the M3 F/R sway bars and said he wished he didn't have the M3 rear bar as the rear would rotate too easily. Over the years, a few 1 and 3 series track drivers have gone back to 13-15mm rear bars as the larger rear bar causes the rear to come around too easily. Those threads are buried here somewhere. Street cars seem to be fine with M3 bars. g/l
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      09-28-2018, 07:28 AM   #35
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Quote:
Originally Posted by cvc 22349a View Post
I wish I remembered the guy's name on this forum a few years ago, good guy who had an E92 with JRZ suspension, track car, 600#F, 700#R and the M3 F/R sway bars and said he wished he didn't have the M3 rear bar as the rear would rotate too easily. Over the years, a few 1 and 3 series track drivers have gone back to 13-15mm rear bars as the larger rear bar causes the rear to come around too easily. Those threads are buried here somewhere. Street cars seem to be fine with M3 bars. g/l
Thanks for the input.

I am currently looking at the UUC SwayBarbarian kit of Front and Rear swaybars. UUC manufactures all the sway bars for the 335d race cars. 27mm Front and 19mm rear diameter. The rear has 2 adjustment settings.
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      09-28-2018, 08:30 AM   #36
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Quote:
Originally Posted by vasillalov View Post
Thanks for the input.

I am currently looking at the UUC SwayBarbarian kit of Front and Rear swaybars. UUC manufactures all the sway bars for the 335d race cars. 27mm Front and 19mm rear diameter. The rear has 2 adjustment settings.
I think the M3 rear bar would be fine with those spring rates and stock front sway. Also, the 19mm solid aftermarket bar is going to be pretty close to the same stiffness as the hollow 22.5mm M3 bar...

I'd like to point out that it is once again someone with 450/700 rates and tcklines complaining about under-steer. I think it's been well established now that you need closer to 400/1000-1200 to keep a more neutral balance. If you want to prove this to yourself then disconnect your front sway and see how that feels as a TEST. The car will roll more but it should be much more neutral handling at the limit. If you like the balance better though then you know what to address.
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      09-28-2018, 09:07 AM   #37
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What if you go through of all these changes, front and rear sway bars and car is exhibiting the same behavior? What if the is the alignment? Like toe in/out, camber and caster?
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      09-28-2018, 12:11 PM   #38
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Quote:
Originally Posted by feuer View Post
What if you go through of all these changes, front and rear sway bars and car is exhibiting the same behavior? What if the is the alignment? Like toe in/out, camber and caster?
Quote:
Originally Posted by feuer View Post
What if you go through of all these changes, front and rear sway bars and car is exhibiting the same behavior? What if the is the alignment? Like toe in/out, camber and caster?
Or tire size, stagger
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      09-28-2018, 11:34 PM   #39
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Originally Posted by feuer View Post
What if you go through of all these changes, front and rear sway bars and car is exhibiting the same behavior? What if the is the alignment? Like toe in/out, camber and caster?
Well, I learn from the mistake and move on. The problem is that I've tried everything that you mentioned, plus tire pressures, tire sizes, etc. Understeer is understeer.
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      09-28-2018, 11:35 PM   #40
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Originally Posted by bbnks2 View Post
I think the M3 rear bar would be fine with those spring rates and stock front sway. Also, the 19mm solid aftermarket bar is going to be pretty close to the same stiffness as the hollow 22.5mm M3 bar...

[b]I'd like to point out that it is once again someone with 450/700 rates and tcklines complaining about under-steer. I think it's been well established now that you need closer to 400/1000-1200 to keep a more neutral balance. [b]If you want to prove this to yourself then disconnect your front sway and see how that feels as a TEST. The car will roll more but it should be much more neutral handling at the limit. If you like the balance better though then you know what to address.
I was also looking into swift springs or getting a different spring rate from TCKline for the rear.
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      10-01-2018, 12:44 PM   #41
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Originally Posted by vasillalov View Post
Well, I learn from the mistake and move on. The problem is that I've tried everything that you mentioned, plus tire pressures, tire sizes, etc. Understeer is understeer.
Ok, so, can you share with us your current wheel/tire setup, alignment, etc. so peeps know what it is your starting with here?

Not sure why this information is so hard for you to provide.
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      10-01-2018, 03:25 PM   #42
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Quote:
Originally Posted by vasillalov View Post
Well, I learn from the mistake and move on. The problem is that I've tried everything that you mentioned, plus tire pressures, tire sizes, etc. Understeer is understeer.
Yes, understeer is understeer but with rear swaybar you won't be currying the understeer per say, you will just make the car easier to oversteer. I highly doubt that the level of mechanical grip on the front will change at all to help car go through corners any faster.
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      10-02-2018, 07:32 AM   #43
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Originally Posted by FCobra94 View Post
Ok, so, can you share with us your current wheel/tire setup, alignment, etc. so peeps know what it is your starting with here?

Not sure why this information is so hard for you to provide.
Sorry. I didn't see anyone asking for it. Here it is:

Tires:
BridgeStone Potenza RE-71R
255x45x18 on the front
265x35x18 on the rear

Alignment:
-3.5 negative camber on the front (maxed out)
-2.0 negative camber on the rear (recommended by TCKLine)

Toe settings are set to recommended values by TCKLine
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