[DeTomaso] Best all-around rear sway bar size

[Peter Havlik]

Mike:

Thanks for your advice and help on this topic, both on the e-mail list and off.
Since this conversation has now spilled onto the e-mail list, I might as well
post my reply to your last private message here as well.

I should have mentioned that my car is a late-model Euro-spec GT5 with a
chassis stiffening kit. It comes from the factory with a 7/8” front sway bar
and a ¾” rear bar. As you know, these cars came with the 10” wheels in front
and 13” wheels in the rear. This means that I can’t apply directly to my
vehicle the lessons from Jack’s, Larry’s and your tests of an earlier model. 

On Dennis Quella’s recommendation, I originally considered going to 1” bars
front and rear because, as you said, he has a lot of experience with the big
tire, wide body cars. However, I then decided to ship my suspension to Pat
Mical for his highly regarded modifications to eliminate the notorious
high-speed wandering and tramlining of post-1980 wide-body Panteras. Pat was
adamant that 1” bars are too much for my application because they are too stiff
and would, therefore, transfer the twist to my chassis instead. He felt my
factory set-up was adequate if combined with slightly stiffer springs. 

I also read an interview that Dave Adler did with Dick Guldstrand in the Spring
2000 edition of PI Magazine, the relevant excerpt from which is as follows:
DA:     I read an article once where I think there was a test at Willow Springs
with I forgot what kind of car that Guldstrand Engineering prepared and then
some other person prepared a car and I think your car was set up, with your
settings in a “shoot-out”. Do you still favor setting up a car soft or hard?

DG:     Not really. The only thing I really favor is not putting great big sway
bars on them because that really
any car that requires a lot of roll couple
like a Pantera or a Corvette, something that’s got a lot of power and
potential, you can’t overcome, you can’t overwhelm that roll couple with a roll
bar because then you’ve tied all of the wheels together and you make it very
unstable in braking and cornering. You load the outside tires too severely so
the balance has got to be about 60% to 65% of the roll couple in the springs,
shocks and bushings etc., and the last 35% or 40% in the sway bars. That’s the
big argument I’ve had with so many people for so many years is that they tend
to make them way too soft and put huge sway bars on them, which is in my humble
opinion, a disaster. Of course we’ve done many magazine articles and shoot-outs
and so on where we’ve won them all. There again, you can’t fool mother nature.
If it works, it works, whether it be NASCAR or road racing or formula one,
there are some basics you have to live with because it is way too easy for
folks to sell great big sway bars.

Being disinclined to argue with Dick Guldstrand, I started re-thinking what I
was going to do. Then I read Jack DeRyke’s article in the March 2006 POCA
Newsletter on bushings in which he wrote:
If the bar is mounted in rubber, such bushings will slightly deflect before
loading up and finally twisting the bar, so the stiffness of an anti-sway bar
is lessened for a given diameter when mounted in rubber. Or, to put it another
way, adding polyurethane bushings to your Pantera will upgrade a given bar’s
effectiveness nearly as much as going up one bar size (0.750” dia to 0.875”
dia). 

Given that I am optimizing my car for spirited touring and not track use, and
based on my balancing of the competing theories, at this point I’m guessing my
best bet is to:
1.      retain the stock 7/8” front and ¾” rear sway bars,  
2.      put polyurethane bushings in the inside mounting brackets front & rear
(thereby effectively going up one bar size), 
3.      install sphere ball outer mounting brackets front and rear, 
4.      upgrade to new fully adjustable gas Konis, and 
5.      use 2 ½” id Hypercoil springs (450lb front and 550 lb rear).

I understand that using the same diameter sway bars front and rear is intended
(and was proven in your test) to reduce understeer in early model cars, but I’m
reluctant to mess with the factory set-up on my car until I know what effect it
will have on a post-1980 GT5 or GT5-S with original 15x10” and 15x13” wheels
(and, therefore, with the original Euro-spec ride height). Of course, the other
wild card in all this is what effect Pat Mical’s modifications to my A-arms
will have -- something probably only Pat can answer and, as I said, he
recommends against changing my sway bars.

Being a rank amateur, I feel like the ball in a tennis match bouncing back and
forth between the experts. I’m not married to my little five point plan above;
it’s just the best sense I’ve been able to make of things so far. In short, I
remain open to any other option, including the use of larger sway bars, if
someone can show me how it will work better specifically on my car. 

- Peter

At 13:23 25/03/2006 -0500, MikeLDrew at aol.com wrote:
>
>In a message dated 3/25/06 9:50:55, kenn_green at yahoo.com writes:
>
><<   You may want to check with others, but one of the most accepted upgrades 
>to Pantera suspension is to go to a 7/8 rear sway bar.  I think it's suppose 
>to make the handling mroe neutral.  You might want to consider that and just 
>get the 7/8 ball ends and a 7/8 rear sway bar.
>   
>  Can anyone else comment on this? >>
>
>>>>Jack DeRyke and I wrote an article covering this in detail more than ten 
>years ago.  Rather than listening to marketing speak which touted the relative

>goodness and betterness of ever-larger sway bars, we decided to scientifically

>test them and collect real data.
>
>Rather than rehashing the contents of the article, I'll just go ahead and 
>copy/paste it here for all to enjoy.
>
>Note that this article was written before the various chassis-stiffening kits 
>were produced--and in fact was itself the impetus for at least one vendor to 
>design and engineer such a kit.
>
>Cheers!
>
>Mike
>
>=====