Can of worms...here we go though!

IMHO a rear bar should only be used on a street car that is autocrossed where you want to pivot the car on the throttle. I had one on my car (5/8" dia) 4 years ago and I took it off at Hallett and left it there in the trash barrel.

If you've ever experienced what you refer to as "Snap oversteer" (and it sounds like you have) it IS NOT a good thing. I have, and let me tell you, NOBODY can save a car from that situation. Imagine driving at the limit at 85 MPH around a long sweeper and with NO WARNING the rear just SNAPS WAY OUT from under you. VERY SCARY as you exit the track BACKWARDS,.... :horror: :horror:

Therefore.... what works for me is...

5 leaf Mustang Plus mid-eye rear springs with a Panhard bar to locate the rear axle AND allow some rear roll center adjustment.

On the front, 620 coils with a large 1 1/8" swaybar.

With this setup, I can easily tune the car to the track conditions by adjusting the rear roll center and balance it for that perfect 4 wheel drift (which is heaven to drive by the way!). I used to run a Watts link out back but the panhard bar is lighter, simpler and more turnable. A panhard bar with a Hotchkiss suspension is not optimal I know, but it works for me. Although I built the one I run, by buddy Robert has a Maier racing panhard bar on his car and it works just as well.

The hard thing is,... trusting the rear again after you've experienced "Snap oversteer"

With this setup, and the panhard bar set about 1" below the centerline of the axle you'll have plenty of oversteer available.

::

 

What confuses me is reading advice not to use a rear sway bar when Mustangs since 1969 (Boss) and stock on all 5.0 Mustangs since somewhere around 1979 have had rear sway bars.

I don't understand why not to use one when they are standard equipment ????

Not arguing. I just truly don't understand.

 

I'm with pprince, the logic behind this seems a bit confusing. I'd also like to know if a big front bar/Panhard bar setup would be good for a very good handling street car?
--Kyle

 

OK, I'm a novice at this stuff and don't have anywhere near the knowlege of roadracer or opentracker to mention a few here on the forum. But I have been doing a bit of reading trying to understand suspension dynamics to make some meaning full upgrades on my 66 for the street. If you look at a coil spring, obvious it's round and no matter at what point you twist or put pressure on it, it's going to react exactly the same. With the leaf spring, look at it like this. As you compress the suspension, the leafs slide on each other given a designed spring rate. Now in a turn as the car rolls in the turn, the body is no longer parallel to the axle but on an angle. This means not only are the leafs compressing but they are twisting causing more binding and an increased spring rate. When the spring is twisted, it's acting like a torsion bar, resisting the rforce being applied. Basically the axle is going to see the same or similar forces as that of a sway bar. Do an experiment. Visualize this, take a pipe wrench and tighten it on the leaf spring on the side and put an extention on it to give you some leverage. Now try twisting the leaf spring. This force is what resist the body rolling in a turn.

Other things to look at is that the rear axle on a leaf sprung car actually "steers" the car from the back. As the leaf spring is either compressed or unloaded from its normal state, the distance from the center of the axle to the front bolt changes and thw axle actually rotates L to R and visa versa to some extend, steering the car.

 

Let me start by stressing the following:

1. This is only my opinion.
2. I do *NOT* autocross or drive my car at the "limit" very often.
3. I enjoy having my car go where I point the front tires.

With those caveats in place - I have a 1" front bar and a 3/4" rear bar. The stock Mustang set-up (65 - the only one I have any direct experience with) has a *lot* of understeer. I don't think anyone will argue with that statement. Just doing the Shelby drop will correct this to a limited extent. But the cars will still "plow" through tight corners. Adding additional resistence to twist in the rear (through whatever means) will "increase" oversteer - i.e., *decrease* understeer.

The choice than is to figure out how to add that resistance. There are lots of options. Everything from Del-a-lum bushings and stiff leaf springs to race track ready IRS systems.

I selected a rear anti-sway bar for the following reasons:
1. It was available and cheap,
2. I could install it,
3. I didn't need an engineering background to design one,
4. I didn't need an extensive shop and testing ground to install and tune it.

It is an adequate option *for me*. If I wanted to do high speed driving at the limits of tire adhesion it would *not* be my first choice. But for commuting and playing around it is great. I turn the wheels and the car follows them nearly instantly. Will I regret the decision? Well I know that when I had my nasty accident in 2002 that the rear anti-sway bar possibly contributed (but mainly it was the Ford Expidition that cut me off and then stomped on their brakes hard enough that their ABS system was on full display) to my inability to control/recover from a skid. But overall I've been very pleased.

I plan to add subframe connectors to the car soon, and will try driving the car with and without the rear anti-sway bar after that addition to see what makes sense then.

Bottom line, I think these cars have way to much understeer and that something needs to be done in order for them to be a reasonably handling car.

With regards to the other questions and twisting and up and down forces both matter. A vehicle that had perfectly designed four wheel steering could go through corners without tire scrub (binding) and so it would respond better to steering inputs - i.e., it would be neutral. Such a suspension is impossible with a two wheel steering system (solid axle, IRS, or anything else) because the two rear wheels are always pointing the same direction so in a turn they will be fighting each other. That tension between the rear tires' seperate paths through a corner will be transmitted or dealt with differently if the car has a solid axle and leaf springs verus something else. I *think* that is what Huskihano is talking about.

John Harvey

 

This was a great help in allowing me to understand the dynamics. I think what I am hearing is that coil spring cars really need a rear sway bar and a leaf spring car doesn't "need" one to the same degree.

Back to my original question, why did Ford put a rear sway bar on their leaf spring cars if some experienced racers here are saying it is better not to have a rear sway bar on a leaf spring car?

 

My experience with rear sway bars on a classic Mustang is NO (or at least with 1966s).
Now, I used to run a 3/4" rear sway bar in addition to my 1 1/8" front sway bar. I liked the setup, however it was because I had so little front grip at the time.
The skinny 205 tires I had on the front had so little grip that the front of my car would still push so badly that the rear of the car being loose wasn't an issue.

Move to current times with a 225 front tire with a lower profile and wow, I instantly had one loose ride.
It was a handful on the street and just scary at the track. First thing I did was remove the rear sway bar after my first track event and I could finally control the ride afterwards. Now, the only time I face oversteer is when I use too much of the 347's torque when exiting corners on the track :winkgrin:

 

Oh ya, here's a great video of my car experiencing oversteer at the track :joker:

http://members.cox.net/2bav8video/autox5_1.wmv (1.1 meg)

 

I guess my Cougar is an exception to the above rules.
1" front bar, 3/4" rear bar. Chinese export brace, Monte carlo bar, KYB shocks. No panhard bar, no subframe connectors, stock rear springs, and 600# 1" drop fronts. Backyard negative wedge 1 3/4" drop.

Rear end is very soft on this car, I feel the outside rear can "dig in" or "hook up" in a turn, also transitions in "esses" are less violent and does not upset the car. Having ridden in other cars, I can feel a violent transition from L-R.

I will say the biggest improvement to the track handling was the negative wedge mod, sway bars, and learning to do my own alignment.
Soft springs, big bars.

I've experienced a poorly designed limited slip unit greatly contributes to oversteer (Powertrax).

And forget about power steering.

 

Good question. Since I'm not an engineer, I can't give the exact reason. But I'll take a some what educated quess from my readings. First off, everything is a compromise in a production vehicle. If you look at leaf sprung cars with rear bars, the bars tend to be much thinner then that of a coil sprung car. Also since you understand now about twisting of the leaf spring in a roll, go one step farther and look at everyhing related. There is a lot of rubber used to absorb harshness even at the front bushing of the spring. This bushing is also getting distorted. Replace this rubber bushing with a aluminum bushing for instance, this is like adding a rear bar since now the leaf spring has less compliance in twisting over all. So maybe Ford added the rear bar since it wasn't praticle to use a aluminum bushing on the steet. Keep inmind that these cars had the suspension tuned to keep us idiots from getting into too much trouble and not for the track.

I don't pretend to know it all but the more I read and understand, the more I realize just how much I don't understand! There's an awful lot going on and you must realize this. Not a personal attack but a general bit of wisdom for everyone including myself. FYI, the book I've been reading is called "Stock Car setup secrets" by Bob Bolles. It's a HP Books publication.

 

Since I'm being quoted in the post of this discusion and do not have the experience as Art or the other guys in road racing, I wasn't trying to make the statement to use or not to use a rear bar but merely state that leaf springs and coil springs act totally different. You can't compare the same size bar from one system to another IMO. Every car is different and they are going to act different and need to be tuned differently

 

I agree.. it's certainly confusing and there is no "right" answer.

On the 1969/70 Boss with a stock rear anti-bar setup....remember one critical thing...

In stock form, Mustangs never came with a way to adjust the rear roll center height and that is the key (for me at least). I use the panhard bar to locate the rear axle (side to side) AND adjust the rear roll center (up/down).

This is what the NASCAR boys call the "Track Bar",.. you know, the one they're always adjusting in the pits "one turn" to "tighten up" of "loosen" the car? Although they do run rear anti-roll bars they rarely adjust them during the race because they are wanting to change the "roll bias" of the car which is the difference between the front and rear roll center heights. Adjusting an anti-roll bar does not do this.... it affects only side to side "roll stiffness"

When you raise the panhard bar you raise the rear roll center. This reduces the distance (which becomes a moment arm) between the center of gravity (CG) of the car and the roll center. In our cars, the CG is ABOVE the roll center. In a turn, centrifugal force acts through the center of gravity and exerts a moment about the roll center defined as the Force x moment arm. More moment ~= "more body roll" ~= more weight transfer ~= a tighter rear end ~= less oversteer.

When the moment arm increases,... so does the moment,.. and so does the body roll... and so does the weight transfer... and so does the tendancy of the rear end to "stick"

So... since for a given speed and corner the Force (centrifugal force) is constant,...how do you increase the moment arm (and thus the "stick")? You lower the panhard bar which lowers the roll center,... and thus increase the moment arm... ... and now you see where this is headed.

To loosen the rear of the car... you raise the panhard bar which raises the rear roll center which reduce the moment arm.... and thus the moment... body roll....weight transfer etc...and well you should get it by now.

Bear in mind, we're talking fractions of an inch here.... I can move my bar up or down 1/4" and feel the difference.

Abeit, NASCAR boys run rear coils and we're stuck with rear leafs which do bind and fight the affect of the panhard bar it does have enough affect to be "tunable". Also, currently "in vogue" in NASCAR is the "soft spring / big bar" camp. The idea being to run very soft springs which allow the car to squat under areodynamic loads and "cheat" the front end down to reduce drag on the straights. You can see this on the short tracks as the front ends rises under acceleration and then drops dramatically to a level well below regulation ride height as they proceed down the straight.

Holy CRAP! :horror:

I just realized this is too much infomation...

(if Art reads this I'll never be able to catch him in that Coog!) ::

 

They cost more, but I used adjustable Stambars. That way I can dial in how much control I want. Tightening the rear makes the steering more responsive. Tighten too much and you'll hook (oversteer). They are also made of spring steel so they are much more efficient than most of the others such as PSTs or whatever. Since body roll is so minimal now I am considering not installing the neg. wedge camber kit I have in the garage. I also use KYB's, GT rated springs for a non jarring ride, subframe connectors, a monte carlo bar and 205/70 14 touring radials. The end result is a nice ride and very good steering response.

 

You can never have too much car related information! Huskinhano, I didn't quote that paragraph in order to disagree or try to prove you wrong.. I just thought it was interesting and worth a discussion.

So far it seems this is the general consensus:

1 - left stock, our cars understeer fairly badly
2 - rear sway bars may be giving TOO MUCH oversteer in conjunction with the leaf springs
3 - panhard bars might provide a middle ground, although I will need to do some more research on that one.

I'm planning on dropping the front 1" and changing over to a roller front end, and possibly a larger front sway bar. I just don't want massive understeer from it. Maybe I should wait on the front sway bar until I get some new leaf springs. Would it be correct to assume that a stock (old) rear suspension and an aftermarket (new) front suspension would tend to increase understeer?

 

Hey guys...this is turning into a pretty educational discussion for the novice guys like myself here. Personally,..like some of the earlier posters,..I was under the impression, that the rear sway bar was a plus....now, having not completed my car yet..and a week or so away from the maiden voyage,..I'm wondering if the rear sway bar on my 68, will only get me into trouble the way 2bav8 was suggesting? Granted I'm not planning on running at the track,...but with 225's up front and 245's in the rear,..and close to 400hp...do you think I will regret having the rear sway bar?

Dan

 

Armon, I'm not upset. In fact I'm a little flattered that someone thought what I said was interesting *G* My main point is to get people to think and not to ruffle any feathers of the guys who know what they are doing since I'm learning as well.

 

I didn't have time to read all the responses, so I apologize if I repeat anything, but I would like to respond to what I did read. I don't think you can say that Mustangs either do or don't need a rear bar. Oversteer and understeer are affected by many things. In this case, we are talking about roll stiffness. Generally, if you increase front roll stiffness, the handling goes towards understeer. If you increase rear roll stiffness, handling goes towards oversteer. This is with everything else staying equal. Armon, does your mustang need a rear bar? Nobody here can tell you that because there are too many variables like tires brand/size/aspect ratio/air pressure, front end alignment, spring rates, weight distribution, ride height, driving style, chassis stiffness, etc...
Only you can make that decision. I do agree with John that these old Mustangs plow badly in stock form, and I think if you were going to make just one change to correct that (understeer, not overall handling), adding a rear bar would be the most effective change. Every car is unique, so you have to evaluate it based on how YOU think it handles. As an example, I have 5 leaf rear springs , 700 lb/in front springs, hard rubber bushings, a 1" front bar, a 3/4" rear bar, and my car still understeers! I'm going to change to softer front springs, which will increase front roll stiffness and move my car further towards oversteer. I don't know if it will get me where I want to be, but it's my next step, because for me my car rides too stiff in the front.
Leaf spring and coil spring cars are apples and oranges when it comes to rear bars, but that doesn't mean you won't find a coil spring car that doesn't need a bar and a leaf spring car that does. Like I said, too many variables to make those assumptions.

 

Well I started this firestorm so here is more info (check 1/2 way down page). http://www.mustangandfords.com/techarticles/29200/

I ran a 66 fastback with fat T/As, Export brace/Monte Carlo bar, Shelby drop, 1" front bar, 3/4" sway bar and Shelby pitman/idler arm, 4-1/2 leaf mid-eye rear springs and all poly bushings. Out of all of these the rear sway bar made the most difference. And I am not talking breakneck autocrossing (although I did that too)..just talking about straightening out some windy country roads at speed. This DOES take some more expertise in driving but nobody should go beyond their abilities anyway. I never experienced 'snap oversteer' whatever that may be...I usually got a very nice 4-wheel 'drift' which is the ultimate in neutral handling.

 

I'll throw a little more heat on the fire... :joker:

Global West and Cobra Automotive do not recommend a rear sway bar.
They are definitely some of the main leaders in suspensions for our classic Mustangs.
Global West goes as far as saying on their website that non of their packages will require the use of a rear sway bar in bold letters.

Also, fat T/A tires are not exactly what I would call a sticky tire.
Wide yes, a good handling tire, no :winkgrin:
Which is probably why the rear sway bar works great for you.
The lack of great front grip would be similar to my previous condition.

And of course, there is never a one size fits all.
There are so many ways to set up a suspension.
One guy will want soft springs and large sway bars, another guy runs stiff springs and small sway bars as an example.
What matters is that you're comfortable with the way the car drives.

I'm just throwing in my experience from the track.
Your individual results may vary :biggrin:

 

I'll throw a little more heat on the fire... :joker:

Global West and Cobra Automotive do not recommend a rear sway bar.
They are definitely some of the main leaders in suspensions for our classic Mustangs.
Global West goes as far as saying on their website that non of their packages will require the use of a rear sway bar in bold letters.

This is my point. You are really misleading people with a statement like this. That ONLY applies to cars with those systems on them, not a stock mustang. One of the reasons these cars plow like they do is the screwed up front end geometry, and aftermarket suspension systems change all of that. Each car is unique. Just because one doesn't need a rear bar doesn't mean another doesn't. Adding a rear bar to a Mustang that has a relatively stock suspension is more likely going to provide huge positive benefits, but whether they are or not is really going to be determined by what the owner is looking to accomplish. It's not about parts, it's about roll stiffness and balance, and there are multiple ways to do that. The original poster doesn't to my knowledge had a Cobra Automovive or Global West suspension, so that information doesn't apply here.

 

Jim...that is true. A Global West setup is a different beast. The point is that you don't really get the benefit of great tires in the curves without decent suspension geometry (read that as rear sway bar for my money). I took the advice from Pete Sessler, author of "Mustang Performance and Handling Guide, 1964-1985" on this topic. Best discussion I ever read on Mustang handling. He advises on putting in a rear sway bar as the first handling mod on all older Mustangs if you want to get the benefit of any other mods (e.g. big tires).

Its hard to describe the increased confidence I had driving "hard" with a rear sway bar installed. I could 'drift' into a turn at speed with neutral handling or downshift & goose it some and break rear traction and power slide around a curve (oversteer) effortlessly. Understeer is usually built into cars so the driver has to 'crank in more steering' at speed and reduces the possibility of 'swapping ends' on a curve (less chance of a liability suit). Neutral to slight oversteer is desirable for performance purposes.