[PaLiAcH]

hey bullitt-heads...

i have heard from a few that the way to go for sway bars is to go with the Saleen Racecraft Front Sway Bar (they say there is no flexing compared with others they have used)... but they were refferring to the GT's and Saleens... how would this sway bar do on a Bullitt, seeing that the suspension the the bullitt is semi-modified?

 

[Barnaby]

What result are you hoping for by adding a thicker sway bar?

The intended result of a sway bar is to equalize the load on your front suspension. Simple answer...The softer the front sway bar, the more front end bite you will have. If you already have understeer(all Mustangs dofrom the factory) then a stiffer front sway bar will only increase that. If you are looking to reduce body roll, stiffer springs may provide a more suitable solution. at least it shouldn't increase understeer, provide they are matched to the rears.
Hope that helps

 

[Vrooom#3440]

I will echo the question: what do you want to accomplish?



The purpose of a sway bar is primarily to limit body roll. It does this by coupling suspension movement between sides. One side goes up, the other wants to up. But in a turn, body roll wants to make one side go up and the other go down. The sway (or anti-roll bar) resists this, effectively increasing the spring rate on the outside going up wheel. This has the affect of increasing weight transfer onto the outside tire.



Now for cornering, the tire only has so much grip to offer. This grip goes up as you add weight to the tire and down when you remove weight. But, and here is the gotcha, it does not go up as much as it goes down. So, ignoring suspension geometry and tire/ground alignment affects, transferring weight from one side to the other will reduce available grip.



We tune handling by adjusting weight transfer. In a stock Bullitt the rear gets a lot of weight transfer by virtue of it's higher roll center, thus for balance it has a much lower anti-roll rate than the front. If you put on a stiffer front anti-roll bar you will A) get more understeer and B) less cornering grip because you have increased weight transfer in the front.



When you start with a pretty well tuned and balanced system, like in the Bullitt, you really cannot make much improvement by changing just one thing. All the parts have to work together to accomplish the desired result.



For example I would like to add a Panhard bar to the back. I think this would greatly improve tracking in the corners by reducing variable rear steer affects. Good so far except that the Panhard bar would lower the rear roll center. This would reduce the rear weight transfer leading to understeer. So now to fix what I just broke I *also* have to change one or both anti-roll bars so as to rebalance the front versus rear weight transfer.



Sorry this got so long, but hopefully it helps folks better understand how this all works.

 

[Barnaby]

Nice explanation.

 

[llama_boy]

thanks Vrooom for the post, this is one of those dark mysterious areas for me.

 

[FordBullitt]

Vroom.. exactly. I have th MM panhard bar and added their adjustable rear sway bar and lower control arms. The LCA's have a sperical bearing at the rear end connection removing unwanted binding. The panhard bar locates the axle more effectively, reducing side load and thus binding on the upper control arms. Lastly, the rear adjustable bar lets me tune roll couple. I have maintained the stock front bar for now until I get done adding coilovers and changing spring rates and rideheight.

As of now, the car is much more neutral than when I tested it at an autocross bne stock where it understeered more heavily.

Brian

 

[Vrooom#3440]

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On 2001-11-15 14:01, FordBullitt wrote:
Vroom.. exactly. I have th MM panhard bar and added their adjustable rear sway bar and lower control arms. The LCA's have a sperical bearing at the rear end connection removing unwanted binding. The panhard bar locates the axle more effectively, reducing side load and thus binding on the upper control arms. Lastly, the rear adjustable bar lets me tune roll couple. I have maintained the stock front bar for now until I get done adding coilovers and changing spring rates and rideheight.

As of now, the car is much more neutral than when I tested it at an autocross bne stock where it understeered more heavily.

Brian

</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>
I came very close to using your car as an example here... I would guess that you have the flattest cornering Bullitt out there since you went the direction of increasing rear roll stiffness.



It is also interesting to note the difference in how the rear anti-roll bar is engineered in the stock versus the Maximum Motorsports versions. Stock basically uses the lower arms as parts of the anti-roll bar. I believe that this has the effect of reducing the anti-roll stiffness since this makes for very long lever arms trying to twist the bar. The MM bar OTOH attaches it's own arms to the rear of the lower arms so that 1)the leverage going into twisting the bar is lower and 2) the effective suspension travel going into the up/down part of the anti-roll bar is maximized. That must be one heck of a stiff anti-roll bar from the looks of it.

<font size=-1>[ This Message was edited by: Vrooom#3440 on 2001-11-15 20:09 ]</font>

<font size=-1>[ This Message was edited by: Vrooom#3440 on 2001-11-15 20:10 ]</font>

 

[FordBullitt]

The stock bar also adds to the suspension bind by acting through the lower control arms and therefore the bushings.

The MM bar I put on is their stiffest. It's 3/4" solid. am currently running it not quite full stiff.

Brian

 

[Vrooom#3440]

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On 2001-11-16 08:16, FordBullitt wrote:
The stock bar also adds to the suspension bind by acting through the lower control arms and therefore the bushings.

The MM bar I put on is their stiffest. It's 3/4" solid. am currently running it not quite full stiff.

Brian

</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>
That setup must require some real finesse on the loud pedal, particularily in the lower gears.

To get tutorial again... remember a few posts back I talked about tires only having so much grip? Well that is in total, meaning that whatever you use for cornering is not available for accelleration or braking. This is how throttle steer works. By applying more (or less) power you vary the grip loading on the rear tires. As the grip loading increases so does what is called the "slip angle", which is basically the difference between where the tire is pointing versus where it is actually going. Just like a wing has a critical angle of attack, a tire has a critical slip angle. We all know what happens when you exceed it.

Now I theorize that Brians setup is optimized to absolute maximum cornering and utilizes a large amount of rear weight transfer to balance it all out. This large weight transfer puts close to the full grip budget toward cornering. So there is not much grip left in the cookie jar for acceleration/braking.

Brian, I believe that you have mentioned less understeer than stock after these changes. To what degree? It would seem that lowering the roll center via the Panhard bar makes a huge difference, perhaps more than I might have expected.

For those interested, I don't know if it is still published. But a great book for explaining this stuff is "How to make your car handle" by Fred Puhn. It has a bunch of diagrams and goes into different designs. A very interesting read.

 

[DHG-1934]

I've been enjoying your "tutorial" very much. I think reasonably attentive and naturally "aggressive" drivers pick up alot of basics about how to make a car handle as time goes by. But sometimes I have to remind myself that there is book learnin' that goes with this. (I've got very little of that, I just like to drive fast.) Though I consider myself an above average driver, I like getting nuggets of information that key me in to things I should study. Clearly the dynamics of cornering and traction is one of those things. I'll look for the book, but in the meantime, Preach On Brutha! :grin:

Joe

 

[FordBullitt]

Vroom..
The main thing with the car now is the rear end is more controllable. Testing ot the sway bar whil back, it pulled a nice 4 wheel drift onto a freway feeder road.

I haven't had the car back to another autocross to see how it compares from before the changes to gauge what degree I have reduced the understeer.

Another good source of information are several books from Caroll Smith.. "prepare to Win" and "Tune to Win" offer great theory and practice on chassis and race car tune.

Chassis dynamics are much more complicated than people think. Rea and research as much as you can.

Brian

 

[mystang99]

this site is awesome!!
thanks vrooom and brian, you gave us very good information.
(and i even understood it all!!-LOL)

 

[Vrooom#3440]

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On 2001-11-16 17:04, mystang99 wrote:
this site is awesome!!
thanks vrooom and brian, you gave us very good information.
(and i even understood it all!!-LOL)

</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>
And that (you understood) my friend is the point and, frankly, real test. There is a trick to writing on b-boards and capturing all the thoughts in a way that they actually come across to the reader. Glad folks have enjoyed it!

Steve

 

[evil428]

Hello Vrooom. Just a quick thought: does adding a strut tower brace under the hood have a similar effect as changing the sway bar sizes/thickness, as you described/theorized?

I remember that the GT's and Cobras of a few years ago all had strut tower/fire wall braces in the engine compartment. Anyone know why Ford may have decided to delete them?

Thanks.

 

[Vrooom#3440]

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On 2001-11-27 20:03, evil428 wrote:
Hello Vrooom. Just a quick thought: does adding a strut tower brace under the hood have a similar effect as changing the sway bar sizes/thickness, as you described/theorized?
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>
Maybe very very slightly. I doubt it would be noticeable in that way. The flex really does not amount to much compared or relative to suspension travel. The flex, and eliminating it, is really more about keeping the rubber aligned with the road :-B And of course keeping the rubber aligned increases grip which is a good thing.
<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
I remember that the GT's and Cobras of a few years ago all had strut tower/fire wall braces in the engine compartment. Anyone know why Ford may have decided to delete them?

Thanks.
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>
I have noted that many of the old iron had braces up front. Sometimes referred to as an import (or was it export?) option.

I would guess that deletion was a combination of cost savings and/or belief that the new body structure was stiff enough without it.

Steve

 

[evil428]

Steve, thanks for your input on the subject. I've been toying with the idea of adding a strut tower brace just for the enhanced grip gained by the reduction in body flex. I like our Bullitts pretty much as they are from Ford, and I'd really love a slightly tighter chassis...but without the inherent increases in understeer associated with the beefier sway bars.

Coming from a '99 Cobra convertible, I was disappointed by how chassis flex and cowl shake there was on that car. And that was just with regular street driving---no racing or autocrossing. Maybe I'm looking for too much tightness right off the shelf from Ford this time around in our Bullitt?

Thanks again!

 

[Vrooom#3440]

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2001-11-27 23:52, evil428 wrote:
Steve, thanks for your input on the subject. I've been toying with the idea of adding a strut tower brace just for the enhanced grip gained by the reduction in body flex. I like our Bullitts pretty much as they are from Ford, and I'd really love a slightly tighter chassis...but without the inherent increases in understeer associated with the beefier sway bars.

Coming from a '99 Cobra convertible, I was disappointed by how chassis flex and cowl shake there was on that car. And that was just with regular street driving---no racing or autocrossing. Maybe I'm looking for too much tightness right off the shelf from Ford this time around in our Bullitt?

Thanks again!
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>
That is very common on convertibles and attempts to fix it are why verts usually weigh more than hard tops.

For an analogy, or experiment, take a cardboard box with an open top and compare it to one with a taped shut top. Major difference in rigidity.

If I can ever get clearance from the tower... here is what I would do for the Bullitt:

1. Add a panhard bar to the rear. Maximum Motorsports claims that the rear end has been measured moving up to 2 inches. This is HUGE! Of course this would require a different rear anti-roll bar at the same time as previously mentioned.

2. Might add offset steering rack bushings. These things are just cheap! I would want to take some measurements first, but given that our cars are factory lowered they probably need offsets. I expect these would reduce bump steer, another of those things that contribute to a loose feel.

3. Add a triangulated front strut brace that ties into the firewall. I expect the difference here to be much subtler. I probably would not be able to tell a difference in cornering. But triangulation of structure is always a good thing and good strut braces give you this. I expect that this would eliminate the little squeak I have now from up behind the dash.

That is pretty much it for a street car. The springs and such are already pretty stiff for general daily street driving in my opinion. You could spend a lot more, there are certainly enough goodies available for these cars to spend money on. And you could get just that extra little bit out. But auto design is always a tradeoff. And for me, this pretty much optimizes the tradeoffs for cost vs. benefit and relative performance vs. daily utility.

Now if I really wanted to have fun, I would transplant the Cobra IRS under the Bullitt. Better geometry, wider wheel track (like the spacers folks are installing), and much less unsprung weight. Sure you might have some wheel hop in 1st gear but I don't spend much time in 1st compared to all of the other gears.

Steve

 

[evil428]

Steve, thanks again for your thoughts. Your presentation of opinions on things are well thought out and clearly written. I, for one, appreciate it.

I agree, the 3-point strut tower/firewall brace is the better choice, and probably the only sensible way to go if I'm going to bother at all.

I just saw a recent post (of an older thread) on a Kenny Brown brace that looks easy AND cheap! I think I'm sold.

Thanks again!