Stephen

iTrader: (12)

Somebody apparently forgot.....Once upon a time, they too knew nothing, nor how to navigate to web to find stuff.

RU1NER

iTrader: (1)

I did search and found sites that sold eibach, moog, etc nothing with a high enough spring rate. Iv'e also since decided to get weight jacks. And just because I have a stereo doesn't mean i don't want my car to handle at all.

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Well as advised I copied and pasted the text "coil springs" into my google bar and the first two 'valid' responses were

www.coilsprings.com/
www.springworks.com/

And the list goes on from there.

Guest

In a static situation this is pretty easy to determine, its in a dynamic it gets really cloudy and the tire temp information comes into play as to where the tire is getting loaded.

RU1NER

iTrader: (1)

If you want to keep debating this, I did see the second link not the first but decided i would go with the ground control weight jacks I guess i should have edited my question from 6 days ago that I figured he ignored.

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blyth18md

Dean's my daddy. Lets not get his temper up. We all know where that gets us. If you're serious you probably have a few stock car parts catalogs laying on the end table already. If not google yourself some free parts catalogs.

RU1NER

iTrader: (1)

I asked for a suggestion on where to get them I didn't say I can't find any springs. And about the jacks it says they work with Suspension spring specialist. And I never asked anything about eibach's. I'm really not trying to argue I asked for a suggestion you're to awesome to give one, end of story.

Stephen

iTrader: (12)

Of course I will! You are so mockable! You singled me out in your post, in a useless attempt at achieving WHAT? To point out what is in my sig, so I am already 100% honest with every here?


#1......600/150s are my starting point & we'll see where I go from there. I already have 3 sets of springs to tune with on the rear.
#2......I've never said my sig pic was anything other than Photoshop, so it isn't like I am trying to pass it off as real
#3......I bought the KBDD SFCs off a member here on TGO, who claimed they were off his 3rd gen. After getting them, I realized they are 4th gen KBDD SFCs. And no....They are not in my hall closet. One of my house water heaters n.

And your point about my weight jack springs & SFCs was....WHAT?

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RacerX13

Thanks for writing all of this Dean-it's really helpful.

I'm not understanding/visualizing this-

By the "ear" are you referring to the A-arm mounting bracket on the crossmember? Or the centerline of the A-arm pivot bolts? A pic would help.


Hope all is well.

Regards, Kris

Stephen

iTrader: (12)

You so funny.....

I've been wrong before, have posted that I was when I am, and will be wrong again. That is just human nature.

You will be wrong sometimes, Dean will be wrong sometimes, everybody in the world will be.......Just the way life is!

RED_DRAGON_85

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//<86TA>\\

iTrader: (14)

this thread needs a clean up of all the BS posts, it has a lot of good info, and its a shame its being filled with childish bickering

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RED_DRAGON_85

dean, i have a question that i dont think you have answered yet.
why is it desireable to have a low roll center? or is it at all?
with a panhard bar rear suspension, the roll center is the intersection of the panhard bar and the differential.
however it seems that the idea would be to get the roll center close as possible to the CG height to reduce the roll moment and body roll...
the only thing i can figure is that you want the rear roll center to be close to the height of the front roll center to keep the rear outer tire loaded in turns
but i keep getting caught in a circle of what-if's and end up back where i started.

sorry if its a basic thing, but i cant seem to wrap my head around it.
also, does this mean that if the roll center were somehow located above the CG, the car would lean into turns?
again, seems impossible, and would only work in a vehicle with a very very low CG like a go-cart, but still...
i keep thinking that maybe the suspension would lean in to the turn but the centrifugal forces would still cause the car body to roll outwards essentially lifting the inside wheels completely off the ground
gah! im so confused.

Norm Peterson

It takes less change in spring rate or bar size to achieve any given change in handling balance. In the extreme case where both roll centers are at the same height as the car's sprung mass CG it would be impossible to tweak that handling with (say) a sta-bar at either end, of any thickness. If there is no roll to start with, a solid "sway bar" that's 3" in diameter would accomplish nothing other than add a huge amount of weight to that end of the car.

In an independent suspension, a high roll center implies a large jacking force that tries to lift the CG (which then causes even larger jacking forces, since the RC also tends to rise). Not really a good thing, especially with grippy tires. Google "swing axles", "early Corvair" and "early VW Beetle". Or take my word for it that you don't want that happening with any independent suspension when you're driving it hard.


Close. The height of the PHB at the car centerline is closer still and good enough for most purposes. To be really fussy, the LCA geometry gets involved and can move the RC either up or down a fraction of an inch from there.


No. See above. You'd be stuck with whatever handling balance comes from the car's front to rear weight distribution and any tire size/wheel width/inflation pressure stagger. You'd be giving up what's possibly the best tuning method in your handling-tweak toolkit.


Load is going to transfer off the inside tires onto the outside ones no matter how much or how little the car rolls. Or even what direction it rolls in. It has to, because the inertia force (car mass times lateral acceleration from cornering) times the CG height are the only things that determines how much roll moment about the ground is happening. Roll rotation is only the visible chassis/suspension reaction to the lateral force, not the cause of that force.

What you're getting into is transient handling balance, before the roll has had time enough to fully develop. At the very beginning of cornering, there is no roll so all of whatever lateral load transfer is going on is going through the roll centers. This thread isn't developed far enough for that part of the discussion yet.


This has been done, experimentally, and I may be able to chase down a picture in the Millikens' book. There are some large disadvantages to doing this - I've seen pictures, and IIRC the tire cambers get really ugly. Keep in mind that lateral load transfer is almost completely independent of how much roll is present (I think the roll angle would have to physically move the CG a significant amount up/down/laterally for it matter at all).


One final thought - the geometric roll centers are NOT the points that the body actually rolls about. Try really hard to separate the forces that cause roll from the roll rotation itself.


Norm

RED_DRAGON_85

after some further research, the guys on the FSAE boards tend to all agree that the GEOMETRIC roll center should be at or within a few inches of the ground regardless of CG.
they also seem to have some feelings that the roll center, weather geometric or force based, is only a small part of tuning and should not be made a big deal of.


what i am referring to is the example of a front wheel drive car with a low front RC and the rear roll rate put way too high, causing the rear inner wheel to lift as much as 3" off the ground in some cases.
while this is required in a front drive car in order to get the *** end to rotate so you dont end up with massive understeer, the effect is opposite in a rear drive car, causing (what would seem) a lot of oversteer... is this correct?
my thinking (erroneous as it may be) is that a RWD handling oriented car will almost always have larger tires in back, so the cars roll axis should slope downward slightly to keep the rear in play, hopefully giving more grip.

brutalform

OK lets knock it off, and stay on topic with this thread, or it will get locked. Questions will be asked in a sticky thread. Its ALMOST impossible to not have any questions being asked, but if they are we have to keep it cool with out any bashing or name calling. First there are two, then four, then before you know it, everyone is at every ones throats. A wealth of info here...lets keep it going.

Norm Peterson

Agreed. Tuning via roll center height tweaking has its place, but ignores changes that you might want to make in the longitudinal effects and ride frequencies. My understanding is the the RC heights are more important during the first couple hundred milliseconds and diminish is elastic effects take over as the roll develops.


You can think of "avoiding massive understeer" as being precisely the same effect as "causing a lot of oversteer", except that they start at different points on the scale from scary-oversteer-if-you-even-blink to understeer that's so heavy that you can hardly get the car to turn at all. In each case, the change is specifically an oversteer effect. IOW, in both cases you're moving toward the scary-oversteer-if-you-even-blink end of the scale without in either case necessarily getting all the way to scary-ville. What I'm getting at is that it's less a matter of where the handling balance actually ends up than it is that both cases are describing the same effect that precisely the same change causes, just in different words.


Not necessarily. That also depends on available power and vehicle weight distribution, and likely the front camber characteristics as well. Not to mention class rulesets in some cases.


The slight slope downward rear to front helps get the rear involved by causing its slip angle early-on to be relatively greater than the front slip angle. You then balance for steady-state cornering by making the front suspension have a significantly higher roll stiffness than the rear suspension does, which helps give you a progression that shifts the handling balance in the understeer direction (note that my mention of understeer here is only intended to indicate the direction that things are changing in, not that the heavy, plowing understeer that most folks think of when that word gets used is what you have to end up with).


Norm

RED_DRAGON_85

i think i understand most of what you are saying.
basically, for autox, set the car up so that with no sway bars, in steady state cornering, it will oversteer, then add bars to bring the balance closer to neutral?

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mike_c

iTrader: (13)

Excellent thread! I thought I had a relatively well sorted suspension...seems I have some work to do.

Norm Peterson

It would probably work out behaving that way.

The front bar on any front engine/RWD/stick axle car is so much stiffer than any rear bar for the same car that if you had a car that was decently balanced with them it would more than likely oversteer rather strongly if you removed them. Says the same thing just looking at it from the final arrangement and going backwards through the development to see where it would have been.

BTW, the above paragraph absolutely ignores the huge rear antiroll bars used by some in drag racing. Cliff's Notes for those things here is that roll is reduced but the handling balance up toward the cornering limit might get rather exciting (and not in a good way).


Dean - I agree that you really do have to start with roll center location. You have to start somewhere, and if nothing else, the sort of spring rates and bar sizes that are going to be reasonable choices depends in part on where the RC's are. Elastic element stiffnesses vs RC height is a big part of discussions that involve relocating rear roll centers (typically lowering them), whether that be due to completely swapping an existing rear suspension arrangement out for something different or simply lowering a PHB or adjusting an aftermarket Watts link.


Norm

radical82

I've been reading through this thread with considerable interest, some very useful information!!!

Though not having the technical expertise of some on this thread, I do have a bit of experience with suspensions and trying to make them work correctly. Roll center on these 3rd Gens seems to be a concern because of the lack of upper A-arm.... but with a bit of research I think I have discovered how to track and graph it properly.

My concern is this, going by the chart in post #50 it would seem that on the third gen's, the easy way to correct and establish a lower RC would be to lengthen the lower arm and put a bit more of a bend on the ball joint end of it to get the inner and outer pivot points equal.... or am I oversimplyfying this whole thing???

I read in one of Vetruck's posts where we used to compensate by stiffening springs!!! How true! and did we ever pay the penalty!!!!

Would you gentlemen consider 5" of overall travel on the front suspension to be adequate on a limited street use type 3rd gen??? Ride isn't that big of a concern, but handling is....I want to try the front coilovers and rack and pinion steering because of the huge weight reduction. Oh yeah, I don't mind a bit of fabrication to get the geometry correct, so how close can I get to "ideal geometry" with a bit of tweaking?????

Thanks for taking time for a newbie on the board!!!

Norm Peterson

Strut suspensions are relatively new to V8/front engine/stick axle cars.

It may help to imagine a fictitious upper arm that is connected to the strut at its top mount and is always oriented at 90° to the strut axis. This virtual arm will NOT be connected to the chassis anywhere, just imagine letting it float around and through anything that might really be there. Its length therefore does not matter, but if you choose something like 9" or 10" your sketch will at least look something like a SLA suspension. You'd probably use this little trick if you were going to set up a spreadsheet to do all the nasty detailed math for you.


RC height comes from the inclination of the lower arm (between the pivot centers, not necessarily along the arm's physical shape) and the fictitious arm that's at 90° to the strut axis. Where those two lines intersect is the front view instant center for that suspension, and lines drawn from the two front view IC's through their respective tire contact patches will define the roll center. Dean's attachment to post #8 shows this.

So altering the LCA slope, inclining the strut differently, or moving the LCA downward at both ends will all move the RC. Keep in mind that changes in strut inclination will directly affect the static camber setting. A longer LCA would affect the rate at which camber changes with suspension motion even if you don't change anything else.

I think that post #50 is more about illustrating that the moveable ends of suspension arms/links move in arcs rather than straight lines.


Norm

radical82

Thanks Norm! I guess the strut suspension intrigues me because of it's simplicity--though I must admit I'm having to relearn a lot of suspension geometry along the way!!!! I've studied Herb Adam's chassis books, his definition for determining RC's is fairly straightforward....saying to draw the 90 degree line you suggest, then an intersecting line denoting the lower arm attach points..... That part I can work out, then the re-education process begins on getting the caster, camber, bump steer, and anti-dive to all work in to the equation in an acceptable manner.... When I get a bit closer on my graphing, I'll post it up, but for now it's draw awhile, then go sit on the floor and move suspension pieces around, then sit and scratch my head!!!!!

Camber gain seems to come into play considerably on the strut front, In trying to compensate for this with the length of the lower arm, maybe I'm just confusing myself???? Not sure if my racing time is a help or a hinderance at this point, but I'm going to struggle through it and hopefully get a lot of insight from you and the others on the 3rd gen forum....

I do keep thinking there is a very easy solution that I'm overlooking--maybe time to just back away for awhile and work on the other end of the car?????

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radical82

Thanks, Vetruck---I actually understand some of that.... So, when the time comes, RC's and CG plotted, components mocked up and the car sitting on the scales I can verify, tune, and tweak adjustments by simulating a side (weight) load on the car and the cross weights as registered on the scale will show the chassis loading????

Guess what I'm asking is, I'm not really much on all the math, plotting, and graphing involved---but when I get a car on the scales and can start playing with component placement and adjustment it all starts making a bit more sense to me.... Then again, I'm more then likely going to fall far short of "the ultimate" suspension, but what I do want is a very good handling front and rear suspension that will perform in a neutral manner.... I don't want to have to throttle steer and dirt track the car through every turn... I've found shocks and their valving to be both a tuning item for the suspension, and also seen them used to cover up some serious flaws in the design???? I would imagine a bit of comprimise is going to be necessary to get the car to perform right on "real world" roads with all their crowns, off-cambers, and the rest of the boo-boo's on a road....

I understand the RC's wheel weights, front to rear weight and transfer, CG's, and IC's---but admittedly most of the rest gets over my head...guess I'd better go back to studying......

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RED_DRAGON_85

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radical82

Again, thanks for your input!!!! It certainly got me back to planning on my own car.... I realize there is no one absolute geometry or mathematics that will apply to all cars in any given handling situation...I guess that's why we all build them a bit different!!!! However, thatnks to the help on this thread I've determined some of my plan is good, some is not so good and it gave me a direction to go!!!!

As for Riley--- I think he built a car I crewed on "a few years back", an IMSA Mustang II owned by Charlie Kemp out of Jackson, Ms... I left them and came back to the frozen tundra to race sprint cars in '76....Often wish I would have stayed with Charlie, but then we all have 20/20 hindsight!!!

Anyway, thanks a lot for your input... One other project to get out of the way, then it's on to the Camaro's suspension and another car needing some chassis work for the winter... Thanks for making me think!!!!!

RED_DRAGON_85

you know dean, i am sorry but its called a sense of humor.
it was a joke and thats it. had nothing to do with actual (or make believe) physics, dynamics, ect... thats why they call it a joke


btw, just went and cleaned out my "bs" just for you!
happy?

Norm Peterson

Worse yet, once some tire lifts clear, whatever further lateral acceleration that might develop is transfered at the other end, without letting the airborne wheel back down. The "down" corner at the end with only one wheel down has nothing to transfer load to, so it just throws it to the other end.


Is or was half of "& Scott"?


Norm

Norm Peterson

Even the guys who can do that, still need to have test drivers get out there and actually drive the damn thing.

As far as I know, the engineering solution always gets tweaked. It may start out being closer than just throwing things together, and it will provide some idea how much you need to change "X" by in order to get "Y" change in the vehicle behavior, but it is not at all likely to be a final solution.

Test driving and a little "gut feel" is always going to count for something.


Norm

luke j

iTrader: (1)

This is exactly what I have been looking for, thanks.

MT91Camaro

Lots of info here, and to be completely honest....I'm completely lost. I just picked up a 91 RS w/ a V6. I plan on putting a SBC w/ T-56 trans in the future.

I understand some of it....(damn I wish I could go finish chassis fab at Wyotech).

Anyhow, most of it makes me scratch my head.

Risewar

I'm just starting my project and have realized I don't have the time to complete a beautiful suspension as described. I am considering using pre packaged parts and have a few questions. You don't recommend coil overs. I was always told coil overs are the way to go. Reading this post is making me rethink. I don't understand how the spring and strut turn while turning. I was looking into getting the Spohn Tubular K-member/A-Arm/Coilover package w Pinto manual rack steering. Would this be a good idea? Is there a better package to get? Rack and pinion VS Stock w/ replaced steering box?

Also, I hear good things about the Hotchkis Rear package. Any input?

Lastly, Subframe connectors?

I had my 88 Trans Am off the road for 3 years and bought a house with a 4 car garage hoping to get cranking on the car, but the house needed the work first and now this first time I'm able to work on it. I would like to get the car on the road soon. I would apprieciate any info.

Norm Peterson

The body of the strut is fixed to the steering knuckle and ultimately the wheel. When you steer, the body end of the strut turns through up to maybe 30-ish degrees either way, while the center rod of the strut does not turn at all. Since the lower end of a C/O spring has to sit on the strut body, and supports against the chassis you have to have some sort of mechanism between the spring and one of the seats to let that 30° happen without trying to twist the spring.

Production strut bearings that permit free steering rotation used in cars with true Mac Strut suspensions (where the spring is coaxial to the strut just like a C/O spring is, only they are bigger diameter) are in many cases of questionable durability.


I don't have any idea how well a Pinto manual R&P would work, but as I recall it was not a particularly fast ratio in that car (4.2 turns lock to lock on a 94" wheelbase car) and might not have as much travel as you'd like if the F-body steering arms are much longer than those in the Pinto. I had a Pinto way back when. Still have my 1972 Ford shop manual set, which might have a little more information in it.


Norm

AM91Camaro_RS

plus with the coil overs, you are limited more on wide tires. You have less room to put wide wheels/tires on the front.

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89_RS

Quick question on weight jacks Dean, is this what you are talking about:

http://www.ground-control-store.com/...hp/II=20/CA=67

Risewar

Thanks for the info. I will be trying this build. After re-reading I decided that this would be the best set-up.

I still have questions about the steering. From what I understand, the rack and pinion setup is the lightest and claim to have the best steering response and fastest ratio. I personally haven't compared the two, but I would like any additional info. I have check out some sites that Vetruck recommends for parts (Racecraft, Spohn) and it seems that they consider this the premium steering setup. There wasn't any info on exact ratio. Has anybody ever tried these? Are they the best setup?

Also the K-member. Same companies have K-Members which are lighter than factory. Are they worth the time and money? Are they stiffer?

I plan on starting the the build soon. I already have checked out the Race craft drop spindles and there are three different types. One stock replacement part #300106. Another one for rack and pinion part #300110. And one that is ultralight part # 300114. I need to decide what steering setup I will be using before making the purchase.

Again I would appreciate any info and help. Thanks

SomeGuy25thZ

I have a lot of these parts that you are looking into. I have all spohn front suspension - k-member, tub. a-arms, manual rack, k-member braces (Had to modify one to make the rack work - spohn even tells u to do this) and I also have race craft drop spindles for use with manual rack, front coil overs from Spohn and koni yellow struts.

Someone once told me that the spohn sway bar will not fit right with the racecraft spindles. I have the spohn sway bars but did not get to install it yet so i'll have to see what that is about (if anyone knows about this please post).

Unfortunately, I have only installed everything and have not driven or adjusted ride heights or anything yet. Car is getting body work finished so I cannot tell you how it rides yet. But installation was smooth - i wish spohns rack n pinion kit came out early and came already installed on the rack so everything is powder coated. I had to install the rack after the fact and now there is bare metal showing everywhere and I need to paint these areas where we there are welds for the brackets.

AM91Camaro_RS

IIRC, I've heard that the rack and pinion will give you a slower steering ratio. I don't personally have experience with that setup, though. You don't want to go to a tubular k-member if you're setting up for cornering, it is lighter but it is also less rigid than your factory k-member.