Rear Stay bar 101, Page one (from old site)

[chicane67]

camaroboy69
Registered User
Posts: 1313
(7/6/04 7:17 am)
Reply
Rear and front sway bar 101 (excellent info!)
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I was just curious to what some of you were running for a rear sway bar on your 1st gen camaros or any other cars that didnt come with them.
EDIT: Oh yeah pics would be appreciated too.
Adam
My Website 06-25-04

Edited by: camaroboy69 at: 7/12/04 8:55 am

streetfytr68
Registered User
Posts: 1149
(7/6/04 7:54 am)
Reply Re: What are you running for a rear sway bar?
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Addco 1" mounted to the underside of a 12 bolt.
/Steevo

www.lateral-g.net

carreranova
Registered User
Posts: 44
(7/6/04 8:19 am)
Reply Took it off...
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We had a Hellwig bar on the rear of our road racing 64 Nova but removed it after swapping ends unexpectedly a few times. We ended up with a stiffer rear spring and no bar and it works very well.

chicane67
Registered User
Posts: 114
(7/6/04 11:02 am)
Reply | Edit Re: Took it off...
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Nadda....nothing....ZERO....

If the chassis is sprung correctly, a 'Hotchkis Type' rear live axle does not require a rear stabilizer bar what-so-ever.

**EDIT for speeling

Edited by: chicane67 at: 7/6/04 8:23 pm

67Sally
Registered User
Posts: 547
(7/6/04 7:36 pm)
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Re: Took it off...
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I agree......Rear sway bar requirements depend on both the springs and shocks that will be run with it.
William
Project PonySnake - 67 Mustang Fastback

streetfytr68
Registered User
Posts: 1153
(7/6/04 8:04 pm)
Reply Re: Took it off...
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Quote:
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Nadda....nothing....ZERO....

It the chassis is sprung correctly, a 'Hotchkis Type' rear live axle does not require a rear stabilizer bar what-so-ever.
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Uhh..Tom,
Perhaps you should tell the folks what spring rate you consider correct for a "Hotchkis Type rear live axle". I think most of us are running relativley "soft" leaf springs by comparison. Can't a rear sway bar be beneficial with soft springs?


www.lateral-g.net

nancejd
Registered User
Posts: 249
(7/6/04 8:10 pm)
Reply Re: What are you running for a rear sway bar?
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That was my understanding as well. I thought that spring rate and sway bar rate sort of have an inverse relationship to each other.
James

zbugger
Registered User
Posts: 1546
(7/6/04 8:19 pm)
Reply
Re: What are you running for a rear sway bar?
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While you're at it, can you describe how tire/wheel width has an affect on that too?
- Allen

chicane67
Registered User
Posts: 124
(7/6/04 9:08 pm)
Reply | Edit Re: What are you running for a rear sway bar?
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Quote:
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Perhaps you should tell the folks what spring rate you consider correct for a "Hotchkis Type rear live axle". I think most of us are running relativley "soft" leaf springs by comparison. Can't a rear sway bar be beneficial with soft springs?
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This would depend on the front spring and stay bar rates......to give you an applicable answer.

If you were to use a spring less than 240 lb/in, I might think about one.....depending on how the chassis drives. I might use (an outside might at that) a 1/2" bar but I wont just put one on a car because I think or hear its a good idea. You have to drive the car and tune it before you just slap a 1", or any bar on it and go. Most "of you" running softer spring rates like the "Ford approach".....soft spring big - stay bar. I dont. Spring correctly and compliment with a stay bar and shock valving.

I'll give you the recommended 'general racing' rates for springs and stay bars, for the first gen. This information has been compiled for street and in a racing class chassis for over the last 35+ years, so this isnt just my opinion:

Street use:
Front spring- 550 lb/in
Front bar- 3/4 to 1" (depends if autocrossed)
Rear spring- 220 lb/in
Rear bar- none

General use:
Front spring- 700lb/in
Front bar- 3/4" or 9/16" or a 1"
Rear spring- 300 lb/in
Rear bar- 1/2" to 9/16"

High load:
Front spring- 900 lb/in
Front bar- 7/8" to 15/16"
Rear spring- 390 lb/in
Rear bar- 9/16" to 3/4"

I myself run a 720 / 320 package on my 67 and I find NO reason what-so-ever to install a rear bar. With the shock technology we have today AND the bushing technology we have today.....there is really no use for one in my eyes.

Mind you that these are recommendations for 15" wheel and tire combinations and tires from years ago. Now, combine todays available shocks, suspension bushings, wheel and tire packages.......and the need for a rear bar is nill. Unless you have thrown in a 9" boat anchor for a differential.....

As you see by the "recommended" rates, the size of stay bar goes up with spring rate. Not the inverse. And honestly, a 1/2" bar isnt worth the weight of the material it is comprised of.

Bugg~ I can not put together a simple answer to your question at this time. There are way too many variables to give a simple answer.......unless David can throw one in off the top of his head. But it will take me some time to word a 'readable' answer to this question. I'll get back to you on that.



streetfytr68
Registered User
Posts: 1154
(7/7/04 5:50 am)
Reply Re: What are you running for a rear sway bar?
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Well that's a real eye opener. I will yank the rear bar and take it for a spin. Explain why spring rates and sway bar rates inversely proportional. Softer springs are more prone to height changes. So I figured that a bigger bar complements soft springs.

My rear sway bar has been in place through many combinations of springs, shocks, wheels, and tires--almost 20 years. I haven't given it much thought, to be honest.

My springs are softer than your recommendation all around, track width is pushed to the limits, tires are 35 series, shocks are 12 way QA-1's. And the chassis is stiff thanks to a roll cage and subframe connectors. So overall, I see no reason not to yank the rear bar.

I look forward to tuning my combination when I get out your way.
/Steevo

www.lateral-g.net

Norm Peterson
Registered User
Posts: 154
(7/7/04 7:14 am)
Reply Rear springs vs bars
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I thought that spring rate and sway bar rate sort of have an inverse relationship to each other.

That's true, but only after you've established how much of the lateral load transfer (LLT) that you need or want happening out back. In turn, that depends on what you've done to the front in terms of springs and bar. And on the roll center heights too (the Guldstrand mod affects the front RC a bit).

You also don't want the sta-bar to be responsible for too much of the rear LLT (it'll lift the inside rear wheel) or too little (if it's so thin that it would only add another 15 lb/in of wheel rate you might as well just use a little more spring instead).

Actually, the Hotchkis leaf spring arrangement already acts a little bit as a sta-bar, particularly if stiff bushings are used in the front eyes.

Norm

Edited by: Norm Peterson at: 7/7/04 7:19 am

chicane67
Unregistered User
(7/7/04 1:23 pm)
Reply rate vs. rate
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Norm hit it right on the head.....it is more CG and RC height related......than spring rate related.

The relationship that the rear has to the front is where roll couple distribution, roll center migration and the respected distributed weight balance has the largest effect.

My reasoning for no rear stay bar, comes because of my spring design and years of tuning that spring to the overall chassis configuration. The spring design has enough rate to handle the power/torque of the specific chassis, it has anti-squat built into it and it's design also controls the IC. All of which have an effect on roll. The Hotchkis stuff is close and it works well for moderate power applications, but it could be ALOT better.

The front to rear rates that I have noted above yield the best results without the use of extra parts........extra parts adds and creates unnecessary sprung and unsprung weight.......which requires less shock valving and tuning. But in the end, the basic suspension needs to be tuned for it to yield the greatest results ~BEFORE~ any additional parts are considered.

It will save you time and believe it or not.....money.

Mean 69
Registered User
Posts: 56
(7/7/04 2:48 pm)
Reply Nice tech!
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Seems like there is more and more tech on this site, I'm liking it.

Just to add a bit more info, for what it is worth. Tom, is 100%, absolutely correct in his statement that the sta-bars (front and rear) come last in the overall tuning of the suspension. At least, that is the philosophy of the folks/literature I trust follow. Spring the car to keep it from bottoming out over the intended conditions, damp it correctly through shock tuning, and then fine tune the system using the appropriately sized sta-bars. Note, this doesn't mean try and do all of this without any sta-bar installed, it merely means that the tuning of them comes last.

So why do we need a front sta-bar, even if we don't need a rear one? Is it because of all that mass up front? Is it because of the smaller tires? Partially, but not mostly. Sta bars are designed to do one thing, resist roll. They will add a bit of spring rate in most cases, but this is because of friction, an unwanted consequence of using poly bushings (race cars use bearings in this location instead).

The amount the car wants to roll depends upon a couple of things. Obviously, the lateral acceleration will have an impact, it is customary to use 1G for lateral loading in calcuations, etc. All lateral forces are "felt" at the CG, so that is obviously a very important number, and is usually of the order of 18" or so for a typical sedan. The next important thing is the roll center, which is where the car will want to roll due to the suspension. The front of the car will have a different roll center height than the rear, and 99% of the time the front is lower than the rear (the other 1% of the time is due to people doing things that they flat don't understand). Anyway, the vertical distance between the roll center, and the center of gravity is called the roll moment. The longer the roll moment, the more the car will want to roll for a given lateral force.

Back to the front versus rear. The front roll center of a well executed car is usually an inch or so below ground level, to about three or four inches above. So the roll moment is relatively large. On the rear of a leaf sprung car, the roll center is found by intersecting a line through the front and rear leaf spring bushings, where this line intersects the rear axle centerline is where the RRCH is. A guess is that is around 14" or so, which means that the rear roll moment is alot smaller than the front, which means for a given lateral force, it will roll alot less. Yes, there's weight distribution, and alot of other factors to consider, but this is a start (you have to start somewhere). There are well documented steps to calculate the front to rear roll bias, weight transfer, etc in the literature. In addition, the nice full car suspension software packages will perform this for you too.

So, back to the original question, what type of sta-bar do you run? Obviously it depends. Does your car push, is it neutral, or is over-steer prevalent? On my car, I run (ran) the full Hotchkis deal, with no rear bar. Worked pretty well, but like Tom, I feel that it is a bit too much on the soft-ish spring, big front sta-bar approach. I am in the process of converting the rear suspension on my car from leafs to a link/coil-over arrangement, with highly adjustable rear roll center height. I expect that even with a similar spring rate to the Hotchkis leafs, due a lower roll center height, that I may need to run a small-ish bar. Time (and tuning!!!) will tell.

Steevo, I'd be interested in hearing how your car feels without the rear bar, if you choose to experiment. Just take slow steps, there may be a big difference in the way the car handles, be careful.

Mark

CarlC
Registered User
Posts: 182
(7/7/04 3:35 pm)
Reply Spring, sprang, sprung...
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OK Tom, you asked for it in the past....

Let's use mine as an example. Track days 2 times/year, agressively driven most other times.

It's no lightweight, but is typical of most PT setup cars:

With driver and full tank of gas:

Left-front 1025#
RF 958
LR 864
RR 861

Total weight 3707#, 53.5/46.5% F/R

700 #/in front springs with Landrum adjusters, Hotchkis hollow bar, Bilstein F4-B46-1104-W000 (Guldstrand slalom), del-a-lum, G-mod.

Guldstrand leaf springs (175 #/in?), del-a-lum, Bilstein AK2074 (737 0493 H002 stamped on shock body, Guldstrand slalom), weld-in connectors.

Engine makes 400+ ft-lb to the rear wheels.

Given this scenaro, what's the best plan of attack to make the car better balanced but still not be a kidney beater?

Also, why do the Mustangs tend to run less rear spring? Seems many of them run max 180#/in. Doug at GW told Torker and I at SEMA that springs over 175#/in on F-bodies are not necessary, even the trick spherical bushing/CAT5 setups. I'm not trying to start an argument, just trying to learn/figure out the right way to take a good car to the next performance level.

Mean 69
Registered User
Posts: 57
(7/7/04 3:40 pm)
Reply What do you want to change?
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Carl, I was under the impression that you were pretty happy with your car. What aspect do you want to change, and what do you mean by making it better balanced?

Mark

CarlC
Registered User
Posts: 184
(7/7/04 5:31 pm)
Reply Ignorance is bliss
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Mark,

I dig the car, but I could easily be overlooking/don't understand how well the overall system could be working.



It's got a lot of neat stuff, but are there subtle changes (spring rate, shock valving, etc) that could be made to make it work together better? Many of us bolt on "trick" stuff, but it's really hard to understand and make it all work to the best of it's ability.

I used mine as a test case since it has a lot of "trick" parts, but how well do they compliment each other? That's what I don't know, and would like to try and figure out without spending another $bazillon.

streetfytr68
Registered User
Posts: 1157
(7/7/04 7:20 pm)
Reply Re: Ignorance is bliss
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Carl,
Post your wheel & tire specs as well. I'm curious how tire sidewall affects spring rate selection.
Mean,
I'll yank the bar and mess around with shock damping. Hopefully on Friday. If not then next week. I'll measure fr and rr roll center height as well.

www.lateral-g.net

CarlC
Registered User
Posts: 186
(7/7/04 8:40 pm)
Reply Tires
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255/50/16 and 245/50/16 BFG Comp T/A ZR.

With -1.8* camber, 6.5* castor, and 3/16" toe out the track tire temps, using Pozzi's temp probe, were reasonably consistant across the tread using 39psi cold front, 38psi cold rear. Even with this much camber there appears to be some excessive outside tire wear, but some of that came from pushing the car too hard.

davidpozzi
Moderator
Posts: 1220
(7/7/04 10:05 pm)
Reply
Re: Tires
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Just disconnect one link on the bar to disable it, no need to completely remove it for a test.
Typical spring rates measured at the front wheels are 100 - 200 lbs/in even with 700 lb coils, tire spring rates are above 1000 lbs, if I remember right. Changing tire pressure changes their spring rate but it's felt most on very stiffly sprung cars running on banked tracks. I've seen guys changing tire pressure by a pound at autocrosses, but for me on my Camaros it just wasn't that sensitive.

Carl, I think your Camaro has a little understeer, it seemed you had more times where the front pushed a little than where the rear swung out. I don't think it's badly out of balance but some experimenting would help point the way. Of course, how you enter the turn can greatly influence how balanced the car acts too, so pay attention to the balance in steady state corners where you are not accelerating or decelerating.
David
67 RS Camaro, 69 Camaro vint racer, 65 Lola T-70 Can-Am vint racer.
ourworld.compuserve.com/homepages/David_Pozzi/

jon
Unregistered User
(7/8/04 6:55 am)
Reply x
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here are my numbers;3200# w/full tank,driver.265/50/16 front 275 40 17 rear.hot pressure target is 39 psi.dse uppers relocated with the dse jig.koni 30 series coil overs with bottom moved to 11.5" from pivot,for a motion ratio of .741(.513 correction factor),with 300# spings(that is about 538# conventional coil,doing the math in my head).hotchkis hollow bar.rear leaf,176#,rubber bushing in front,poly for shackle.pro shocks,set at 5/6.i tend towards understeer,if i let more air under the nose it is pretty good.i need a wing.bottoms slightly in the on ramp at buttonwillow.

camaroboy69
Registered User
Posts: 1328
(7/8/04 10:49 am)
Reply
Re: x
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awesome information guys!!
Adam
My Website 06-25-04