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Input needed (suspension build)

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Old 01-13-18, 07:57 PM
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Input needed (suspension build)

Iíve fallen into the dark hole of forum researching, and I need to slow down for a sec and make sure that Iím not missing the forest for the trees.

85 FB GSL. Currently all stock suspension. End goal is an aggressive street setup. Weekend toy, not DD, but not planning on tracking it.

Purchased so far:

- Full T3 coilover package (250# / 200#)
- panhard bar conversion
- complete Energy suspension poly kit

I was feeling confident at the direction I was headed but canít seem to get a straight answer on the poly bushings. Have run them in other builds, but never an rx7. No big deal? Terrible idea?

Sways. With the spring rates Iím going to be running is there a suggested front and rear thickness that would match up well?

Tire/rim package will be 15x9...

any input or suggestions appreciated.
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Old 01-13-18, 09:01 PM
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The more I realize that my car will be just a weekend get-away car, the more I understand what I need to make it acceptable for the task. For a weekend non tracked car, you are going a direction that surprises me. I plan on using a hybrid of rubber and poly, though I am still working that out. What surprises me is the 15x9 wheels. I do not believe I have seen a Rx-7 of our vintage with wheels that wide with out a Mariah Mode1 or IMSA kit or something.
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Old 01-13-18, 09:26 PM
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15x9 wheels will not fit unless you have some big fender flares or a widebody kit.
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Old 01-13-18, 09:56 PM
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Dp

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Old 01-13-18, 10:01 PM
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Originally Posted by Richard Miller View Post
The more I realize that my car will be just a weekend get-away car, the more I understand what I need to make it acceptable for the task. For a weekend non tracked car, you are going a direction that surprises me. I plan on using a hybrid of rubber and poly, though I am still working that out. What surprises me is the 15x9 wheels. I do not believe I have seen a Rx-7 of our vintage with wheels that wide with out a Mariah Mode1 or IMSA kit or something.
Iíll try and explain a little more....see if it makes more sense?This car will be my street legal ďraceĒ car. No long road trips, probably best described as an autoX style setup without being specifically set up to autoX? I want it to FEEL racey while being incredibly visceral. I have a 13b TII being massaged to drop in and I want the suspension to keep up with the power. I live in an area with fantastic mountain roads, I want to enjoy them.I have a classic Volvo that is my weeknd cruiser, I want this to be...... a whole different beast.Does it make more sense now? Does the direction Iíve gone match my desired goals?Thanks for the input....Oh, and yes, fender flares 😎👍
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Old 01-13-18, 10:29 PM
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Im running 275/150 springs in my +400rwhp fb. Tokico Illuminas. Those rates were based on recommendation (RE-Speed before they went down the tubes) for track friendly street use pretty much as you describe. Im also running castor blocks or roll center correctors whatever you want to call them. Urethane all around and a panhard. It all works very well, but I have ripped a trailing mount off the diff once before, possibly due to the urethanes but also possibly due to the powaaaah. It is probably an idea to use rubber in the upper arms, or drilled urethane, although i was playing with the diff articulation with no shocks or springs recently and there was no binding, but those urethanes were definitely getting tortured!
Also have a whiteline front swaybar on the softest setting which works well. Did have it on hard but soft is much better. No rear sway bar.
Fitting 9's will be a struggle without flares or a roll, at the front at least. 8" and 225 will be about the limit at the front with careful offset choice.
Also have Ground Control strut plates, about -2deg camber, 6deg castor.
Whole package works very well, but let down by the craptacular steering, especially with the extra castor at low speeds.

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Old 01-13-18, 10:58 PM
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Very helpful, thanks.

i find the 275/150 interesting... T3 has recommended the 250/200. Pretty easy to change out springs if needed though, so not a huge deal.

Do you have a build thread? What wheel/tire combo are you running?
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Old 01-13-18, 11:10 PM
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No no build thread sorry. Those spring rates are probably the softer end of the spectrum, but you definitely do want the rear a fair bit softer than the front. It handles pretty neutral, of course oversteer on demand under power or trailbraking. Im on 7.5's and 225/45/15. toying with the idea of getting 8.5's in but i dont think it will happen.
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Old 01-14-18, 11:35 AM
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Do something like this. SA22C RX-7 part 2 | JDM Legends
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Old 01-14-18, 01:17 PM
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Originally Posted by KansasCityREPU View Post
Do something like this. SA22C RX-7 part 2 JDM Legends
Oh buddy, amazing. Definitely some of the vibe Iím going for.....
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Old 01-14-18, 01:44 PM
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Originally Posted by 2tall4u View Post
I’ve fallen into the dark hole of forum researching, and I need to slow down for a sec and make sure that I’m not missing the forest for the trees.

85 FB GSL. Currently all stock suspension. End goal is an aggressive street setup. Weekend toy, not DD, but not planning on tracking it.

Purchased so far:

- Full T3 coilover package (250# / 200#)
- panhard bar conversion
- complete Energy suspension poly kit

I was feeling confident at the direction I was headed but can’t seem to get a straight answer on the poly bushings. Have run them in other builds, but never an rx7. No big deal? Terrible idea?

Sways. With the spring rates I’m going to be running is there a suggested front and rear thickness that would match up well?

Tire/rim package will be 15x9...

any input or suggestions appreciated.
Absolutely ZERO Polyurethane is the way to go.

I'd suggest 325lb Front, 175lb Rear.

Take off the Front Swaybar and run a LARGER Rear Swaybar (24mm ish for your spring rates should work nicely)

245/40-15 Rear and 225/45-15 Front on those wheels will be nice.

Panhard Bars are okay, but the real geometry issue is the links themselves (huge pinion angle change). Ideally you'd change geometry with drop-brackets (I will produce a kit in Q3 2018) and create an equal length Watt's Link (check out Winfield Coachman's build aka Elwood).

Definitely check out my build. I think I just saw you Subscribe to my YouTube channel too.

Cheers,

Ryan
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Old 01-14-18, 02:08 PM
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But your car doesnt work yet dude. Its all theory. As to urethane, apart from rear binding issues on stock geometry, it is a day and night improvement everywhere else.
As to the idea of no front bar and heavy rear bar, that is the opposite of what decades and decades of trial and error by racers and tuners the world over would have you believe.
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Old 01-14-18, 02:27 PM
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Originally Posted by SirLaughsALot View Post
Absolutely ZERO Polyurethane is the way to go.

I'd suggest 325lb Front, 175lb Rear.

Take off the Front Swaybar and run a LARGER Rear Swaybar (24mm ish for your spring rates should work nicely)
Have you actually employed this setup on a RWD car? Do you have A to B comparisons, lap times, etc as to how this works. Not trying to be a smart ***, I am asking the question for real.

Personally, I have seen the no front sway bar/huge rear bar setup used on front drive autox cars - Rabbits, etc. Works for them as they rotate like a top. Road race FWD cars seem to follow the same formula but not to the extremes that I saw in autox.

I/we have always taken the approach that body roll is controlled at the front of a car. Even my friends 4 time Solo National Championship winning Yenko Stinger Corvair (Charlie Clark - he owns KC Raceware) has a massive front sway bar.
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Old 01-14-18, 11:40 PM
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Originally Posted by mustanghammer View Post
Have you actually employed this setup on a RWD car? Do you have A to B comparisons, lap times, etc as to how this works. Not trying to be a smart ***, I am asking the question for real.

Personally, I have seen the no front sway bar/huge rear bar setup used on front drive autox cars - Rabbits, etc. Works for them as they rotate like a top. Road race FWD cars seem to follow the same formula but not to the extremes that I saw in autox.

I/we have always taken the approach that body roll is controlled at the front of a car. Even my friends 4 time Solo National Championship winning Yenko Stinger Corvair (Charlie Clark - he owns KC Raceware) has a massive front sway bar.
The best way to find out is to disconnect the factory front swaybar endlink and leave the factory rear on.

For ME, personally, I'd prefer a car that's mild oversteer and what I suggested just that.

Originally Posted by WANKfactor View Post
But your car doesnt work yet dude. Its all theory. As to urethane, apart from rear binding issues on stock geometry, it is a day and night improvement everywhere else.
As to the idea of no front bar and heavy rear bar, that is the opposite of what decades and decades of trial and error by racers and tuners the world over would have you believe.
****, I have yet to hear anything positive from you. Your opinion is null. I set up a wide array of vehicles on a daily basis in a region surrounded by race tracks and mountain roads.

Polyurethane creeps in which your concentric hole turns into a sloppy slot within a few hard drives (doesn't matter who makes it - don't bring that argument up). Improvement is laughable. Maybe for 2 laps at Thunderhill before they start to open up, but what do I know, I run custom Sphericals and Bronze/Steel Bushings on my daily driver and it's incredibly comfortable (and outpaces anything on 500 Treadwear Tires).

Well here, let me just show you me putting around at 6/10ths on a backroad. You tell me.


Furthermore, here's a quote from Paul Yaw that I think is appropriate here. You're talking suspension, let's talk Roll Center Height...

A non technical, PRACTICAL description of roll centers.You've probably already read the proper technical description, and so you understand the jacking forces, the assertion that the body rolls around that point, the debate about force based roll centers vs geometrical centers, blah, blah, blah.
You probably also understand that raising the roll center increases the roll resistance at that end of the car, and lowering it decreases the roll resistance at that end of the car, and so it could potentially be used to adjust the overall balance of the car. What is important to understand is that the roll is resisted as a reaction to the jacking force, and you may as well call it anti roll, because it effectively works the same way as anti dive and anti squat.

Now for the important part. Roll resistance from a spring is displacement dependent. The greater the spring displacement, the greater the force, so as the car rolls, it eventually reaches an equilibrium between the two forces, and the car takes a set at its final roll angle.Roll resistance from dampers is velocity dependent, and the resulting roll rate is again dependent on the balance of the two forces.

As you probably know, tuning the dampers is an effective method for changing the transient balance of the car.
Now - back to "anti roll" It is neither displacement, nor velocity dependent, and it resists roll as immediately as the tire will generate lateral force. It is abrupt, in the same way that anti squat and anti dive are abrupt, as the only thing to cushion it is the combined stiffness of the linkages, mounts, etc, which hopefully are pretty damn stiff.

So...if your rear roll center is quite high compared to the front, the response time (And weight transfer) at the rear will also be much quicker, and the driver will spend the majority of his time white knuckled, puckered up, and focused on the rear of the car that always seems to want to come around to meet him.

This is a common situation with the FC RX-7 when you lower it for road racing. The rear roll center mostly stays put, while the front roll center goes below ground. It makes the car evil, and sends all the amateur road racers looking for a fix for the rear suspension, when the real problem is the front.(On that subject, it was SCCA's decision to make my front roll center relocation kit illegal, and return the cars to evil and dangerous, that finally motivated me to take my toys and go home.)

So...it's not about a "good" roll center, it is about how it effects the transient response of the car in roll. Move them both high enough, and you have a kart. Put them both well below the ground, and you have a wet dish rag that rolls like a bitch no matter how much spring and bar you bolt to it. Get one end much higher than the other, and you may as well be driving two different cars, because the two ends each seem to have a mind of their own.The effect on transient response can be even greater than what you can do with the dampers, because even the best dampers are laggy in comparison.

So...you know how you can get heat into the tires with a lot of low speed compression damping? That's nothing compared to how you can warm those bitches up (Or overheat them) with high roll centers.

That's basically it.Unless you're reading this shaking your head, sketching up a free body diagram, planning to walk us through a proper physics based description. If so, don't. Scroll up, and remind yourself that this starts with the word PRACTICAL in all caps...



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Old 01-15-18, 03:48 AM
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Originally Posted by SirLaughsALot View Post
The best way to find out is to disconnect the factory front swaybar endlink and leave the factory rear on.

For ME, personally, I'd prefer a car that's mild oversteer and what I suggested just that.



****, I have yet to hear anything positive from you. Your opinion is null. I set up a wide array of vehicles on a daily basis in a region surrounded by race tracks and mountain roads.

Polyurethane creeps in which your concentric hole turns into a sloppy slot within a few hard drives (doesn't matter who makes it - don't bring that argument up). Improvement is laughable. Maybe for 2 laps at Thunderhill before they start to open up, but what do I know, I run custom Sphericals and Bronze/Steel Bushings on my daily driver and it's incredibly comfortable (and outpaces anything on 500 Treadwear Tires).

Well here, let me just show you me putting around at 6/10ths on a backroad. You tell me.

https://www.youtube.com/watch?v=qRwqnarCUTM

Furthermore, here's a quote from Paul Yaw that I think is appropriate here. You're talking suspension, let's talk Roll Center Height...


TLDR but dude, i do like your build. I love your rear diff and suspension set up. It is ****. But you dont need any more praise as you are your own fan club. And quite frankly, as far as i can tell you havent driven an FB yet and now you are telling everyone to set the swaybars up like its a Honda Civic.
As to urethane, i have had one brand which split and cracked up. The brand i have now (superpro) is as perfect as the day i installed it years ago. Bits and pieces have been out of the car here and there and there and on inspection the UT bushes are still brand new. Not many people will want solid bush and rod end suspension for the street.
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Old 01-15-18, 06:00 AM
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At stock ride height or lower, I would not go any stiffer on the rear springs unless the front was getting significantly stiffened.

The problem is the rear suspension doesn't like to articulate. So the car turns into a snap oversteering pig when you get any body roll. Without major surgery, the fix is to focus on keeping the front suspension from moving much.

I like having a rear bar on cars with the stock 4 link because it makes the oversteer problem much more progressive, it hinders the articulation that the high roll center can enforce. But stiffer springs in the back without significantly stiffening the front will result in cornering like a Corvair. Lifting the inside wheel and jacking the ouside wheel under high cornering load when the signs reverse is SCARY! (I have only had this happen with grippy 225/50-15s on the car. The high grip and tall tires seemed to exacerbate the geometry issues)

Fortunately a well designed Panhard will help that. What roll center are you going to go for? That alone will determine what spring rates you should use in the back, although you can't go very low without running into other geometry problems until you throw away the upper links.

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Old 01-15-18, 11:26 AM
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Originally Posted by SirLaughsALot View Post
The best way to find out is to disconnect the factory front swaybar endlink and leave the factory rear on.

For ME, personally, I'd prefer a car that's mild oversteer and what I suggested just that.
I inadvertently "experimented" with this at a Solo Nationals in the late 90's. The C Prepared Mustang I was driving broke a front sway bar end link. The car drove okay but would not get off of a corner because it was unloading the inner rear tire. We figured the Auburn differential had died so lived with it. Found the sway bar end link later.

Another "experiment" was with my 2012 Mustang street car. I put on much stickier tires which increased body roll quite a bit and this also affected rear end grip. The car got better when I installed stiffer Boss 302 front springs with no other changes.

My takeaway is that balance needs to be a consideration and that often times a change at one end of the car affects the other end to a greater extent.

+1 for Peejay's contribution to this thread.
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Old 01-15-18, 11:56 AM
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Originally Posted by WANKfactor View Post
TLDR but dude, i do like your build. I love your rear diff and suspension set up. It is ****. But you dont need any more praise as you are your own fan club. And quite frankly, as far as i can tell you havent driven an FB yet and now you are telling everyone to set the swaybars up like its a Honda Civic.
As to urethane, i have had one brand which split and cracked up. The brand i have now (superpro) is as perfect as the day i installed it years ago. Bits and pieces have been out of the car here and there and there and on inspection the UT bushes are still brand new. Not many people will want solid bush and rod end suspension for the street.

Hard enough to do this.

Tuning this...

I mean, yea, it's not MY car, but I have setup 3x FBs for various usage. They're actually pretty damn good out of the box at factory ride height. The problems come when you lower them extensively.

Too Long Didn't Read is going to be a drawback for you, because I know you've been incredibly helpful on this forum in the past and you yourself have a badass build (thank you for that awesome praise). Look, if you go on ANY forum there's going to be a large variance of opinions and egos to deal with.

Opinion 1: Heavy *** Spring Rate + Huge ARBs (This guy wants the feeling of death for his street driven "race car")
Opinion 2: Soft Spring Rates + Huge ARBs (Really fun, very controllable for 90+% of the users = Great on street)
Opinion 3: It's all in the geometry, spring rates are "meh" of an issue
Opinion 4: Moderation is everything, Moderate Spring Rates and independent front suspension (no front ARB) are key to improved droop (contact patch on road when it gets bumpy) = This is where I land. Personally, I'd run more low speed compression to deal with any body control issues and make sure that front can articulate to the bumpy *** road it's being driven on. I like the rear swaybar to remain light (thin) for the exact reasons that PeeJay mentioned above. At the end of the day, I'm building versatility and compliance.
Opinion "n" .... There's always another opinion.

Cheers, Gents. I hope that helped, Mark.
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Old 01-15-18, 12:42 PM
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Thanks everyone, some very helpful input to digest.

peejay- I’m planning on running the T3 rollcenters....

I’ll be getting the ordered parts on before too long, but might be summer before I really get out and have a chance to push it a bit and report back. We’ll see where we end up!
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Old 01-16-18, 01:17 AM
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Originally Posted by SirLaughsALot View Post

Hard enough to do this.

Tuning this...

I mean, yea, it's not MY car, but I have setup 3x FBs for various usage. They're actually pretty damn good out of the box at factory ride height. The problems come when you lower them extensively.

Too Long Didn't Read is going to be a drawback for you, because I know you've been incredibly helpful on this forum in the past and you yourself have a badass build (thank you for that awesome praise). Look, if you go on ANY forum there's going to be a large variance of opinions and egos to deal with.

Opinion 1: Heavy *** Spring Rate + Huge ARBs (This guy wants the feeling of death for his street driven "race car")
Opinion 2: Soft Spring Rates + Huge ARBs (Really fun, very controllable for 90+% of the users = Great on street)
Opinion 3: It's all in the geometry, spring rates are "meh" of an issue
Opinion 4: Moderation is everything, Moderate Spring Rates and independent front suspension (no front ARB) are key to improved droop (contact patch on road when it gets bumpy) = This is where I land. Personally, I'd run more low speed compression to deal with any body control issues and make sure that front can articulate to the bumpy *** road it's being driven on. I like the rear swaybar to remain light (thin) for the exact reasons that PeeJay mentioned above. At the end of the day, I'm building versatility and compliance.
Opinion "n" .... There's always another opinion.

Cheers, Gents. I hope that helped, Mark.
Why are those brackets lower than the tyres? That cant be right.
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Old 01-16-18, 11:26 AM
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Oich.

First off, the big problem with the cars at this point in their life cycle is that there's no easy strut solution that's happy with high spring rates. Tokico Illuminas would kind of handle higher rates but were getting really marginal at the rates you need to race these things, and good luck finding Tokico Illuminas anymore. I like the 275/150 split WANKfactor was talking about as that's within the range where the shocks will still work. I have no idea whatsoever why you'd try to ditch a sway bar up front on one of these cars - you're going to have to run the spring rates higher for the same roll stiffness and then you get even deeper into the "no sufficiently good strut" issue along with screwing over the ride frequencies.

The big problem unless you're fabbing stuff ... well, peejay covered most of it regarding binding and snap oversteer. And when you feed more power into it, the short svsa is going to bite too. There's no good fixes here without fab work.
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Old 01-16-18, 01:46 PM
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Originally Posted by Kenku View Post
Oich.

First off, the big problem with the cars at this point in their life cycle is that there's no easy strut solution that's happy with high spring rates. Tokico Illuminas would kind of handle higher rates but were getting really marginal at the rates you need to race these things, and good luck finding Tokico Illuminas anymore. I like the 275/150 split WANKfactor was talking about as that's within the range where the shocks will still work. I have no idea whatsoever why you'd try to ditch a sway bar up front on one of these cars - you're going to have to run the spring rates higher for the same roll stiffness and then you get even deeper into the "no sufficiently good strut" issue along with screwing over the ride frequencies.

The big problem unless you're fabbing stuff ... well, peejay covered most of it regarding binding and snap oversteer. And when you feed more power into it, the short svsa is going to bite too. There's no good fixes here without fab work.
1) Don't dump the car. The Roll Center in the front needs to maintain it's height.
2) Compression Controls Body Roll, so that's absolutely not an issue.
3) Freely traveling independent is going to be faster at 10/10ths and 11/10ths... I don't want what's happening on the passenger side to effect my driver side front wheel. That's a terrible idea.

It's not going to be EASIER to drive. ARBs (swaybars) make the cars easier to drive and more consistent at lower loads. I thought you wanted to go fast though?
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Old 01-16-18, 02:21 PM
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Originally Posted by SirLaughsALot View Post
1) Don't dump the car. The Roll Center in the front needs to maintain it's height.
2) Compression Controls Body Roll, so that's absolutely not an issue.
3) Freely traveling independent is going to be faster at 10/10ths and 11/10ths... I don't want what's happening on the passenger side to effect my driver side front wheel. That's a terrible idea.

It's not going to be EASIER to drive. ARBs (swaybars) make the cars easier to drive and more consistent at lower loads. I thought you wanted to go fast though?
1) Front roll center is the easiest problem to fix out of any of the possible issues with the front suspension. Unless you change to FC style knuckles, we're really spoiled for how easy it is to fix.
2) Compression valving on on the shelf shocks isn't the issue. Put stuff on a shock dyno some time.
3) I'd be really interested to see any lap times that support that, if we're talking 10/10ths - none of the runoffs cars in any class I've poked around under subscribed to that belief.

I mean you're entitled to your opinion I guess, but

A) The guy is asking about a street setup, so stop being cute with all this 10/10ths stuff, he's not doing that on the street nor are you
B) The rear suspension geometry is not really compatible with driving 10/10ths on modern tires without more rework than most want to do.

Seriously, there's still a bunch of people still running 1st gens in EProd in SCCA because it's competitive, and there's a very well developed knowledge base of what works and what doesn't... and other than the need to fix the rear suspension, there's nothing that special about it such that some miracle idea of not running a front sway is going to work better here.
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Old 01-16-18, 03:09 PM
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All this talk about rear bars has got me thinking...
My new diff is having the finishing touches put on it as we speak.... Im wondering if i should take my OEM sway bar and brackets down there and get them to tack something on...? Wasnt really planning on ever putting it back on but now not so sure.
Would having a little bit of rear bar make the rear end more progressive you say?
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