JDWalton

All right so I went to a track recently and faired pretty well, but I really am looking at whats going to set me up for the best launch, but I got to thinking about this and want some opinions.

All right, so in a launch you have weight transfer to the rear wheels and create the squat, while at the same time you are creating torsion in the drive-line hence why it squats to the rear and to the right. So I know to counter this the Eibach drag launch kit comes with a air bag so as you reach your squat, it keeps the car from squatting and rotating.

Alternatively, there is the BMR drag launch kit. This kit limits the articulation of the axle by linking a torsion bar with the body.

Now I am already leaning toward the Eibach spring kit, as the soft rear springs as well as the fact that the car isn't lowered, will help with weight transfer and launch. What I am wondering though as a future mod, is how much more traction do you think i would gain with the addition of the drag launch kit? It just seems that with a properly adjusted air bag, the drag launch kit is a second device to do the same job and limit axle articulation at launch.

Thoughts?

EDIT:
Adding parts for clarification:
http://www.bmrfabrication.com/2005MustangSUSPENSION.htm
listed as extreme anti roll bar, but also known as drag launch kit

http://www.americanmuscle.com/eibach...s-2005-gt.html

JDWalton

anyone know what I'm talking about?

MeanStang08

bump..

i'm curious about this myself.. and what about upper 3rd link or those torsion bars in the trunk (tower to tower) or just changing out your lower control arms with stiffer bushings even?

Sam Strano

I know what he's talking about, but the rub is... Those things will wreck handling, and this is the handling section.

If the OP would like to talk about a setup, either full drag, or come compromise that would still make for decent handling he should feel free to call me.

I'll say this: Drag suspensions are only good at drag racing. I don't see much that resembles drag racing out on real world roads, and certainly stability at the top end is not a crucial concern for such a setup, neither is ride... it's all about hooking. A ProStock car wouldn't be much fun to drive on the road.

JDWalton

yeah I know that either is gonna be very bad for cornering, I am looking at a drag setup..... But this section gets used more as a all around s197 suspension specific questions area and is not always limited to strictly cornering. I asked it here instead of the drag section as it seemed more specific. Handling, as in how the car handles (insert situation here), not just how the car corners.

All the items you mention help all around traction by eliminating flex that otherwise fights traction. The items I was talking about are more drag specific. There main point is to assist weight transfer, limit articulation (not what you want ont he street) and ensure that the weight is transfered evenly to the rear wheels so that one does not hook more then the other and cause the car to go sideways at the launch. With the power range your in, you should have the upper and lower control arms already.

The torsion bars are not the same as a strut tower brace like your thinking. The item you mentioned is more for corners by limiting the flexation of the body by linking the tops of the struts. A torsion bar is usualy a steel rod that has fixed mounts on the body, and fixed mounts on the axle. The result is anything more then a few degrees of aticulation on the axle, requires considerably more force, as now it has to flex a thick steel rod.

I really thought I worded a pretty specific question.....

Norm Peterson

I think you're confusing squat with being the cause of rearward load transfer.

It's not. All squat is, is visible evidence that rearward load transfer is happening.

And you can have great initial rearward load transfer that shows either no squat at all, or the tail can actually rise (drag racers call this "separation", indicating the visual effect between the rear tires/wheels and the tops of the fender openings).

Ideally, you want your anti-squat to be right around 100%. When you have that, all of the load transfer happens more quickly than if you have to wait for the suspension to compress. Waiting on spring compression to put all of the load transfer down at the contact patches is what "squat" really means, and that small amount of time can matter.


What that extreme roll bar does is force a lot more of body roll to be resisted at the rear. For a handling application, that'd be bigtime oversteer. But for the drag racer it takes the roll from the engine torque reaction, makes more of that carry back through the chassis to "re-plant" the RR tire (which is going light as the LR is going heavy). The LR gives up a little, but the net difference is an overall gain So the first benefit is more equal tire traction (which gets better still if you also disconnect the front sta-bar). The other benefit has to do with axle roll steer - also more commonly associated with cornering - with less roll, you get less roll steer and the car will leave straighter and require less attention to keeping it pointed in the right direction. But don't bother putting an extreme bar on a ladder bar car (ladder bars turn the axle tubes into a 3" OD tubular antiroll bar - now that's REALLY BIG).


I don't mind seeing a dragstrip topic such as this one show up here. It's still "vehicle dynamics", and the basic geometric and load transfer principles are still the same. Just that with such a different application the compromises and thinking get pushed in a different direction. Getting one's thinking "pushed" is apt to be a good thing.


Norm

JDWalton

so thats a fancy way of elaborating on everything I said already, where the car naturally squats, and both products fight squat to increase traction in there own way, but still manages to sidestep the question.
I didn't confuse anything, but you guys are succeeding at way over complicating a simple question. Stop being autocross experts or engineers for a few minutes and keep it simple.

Now dont read too much into that and get into how they accomplish things different ways, I understand there two different devices, but my point on what they do is valid, and I was originaly trying to get at just how much added grip (roughly) people would think the drag launch kit would add, if there was already a properly installed and adjusted air bag. Reason being, to see if the added cost would be justified by performance.

Norm Peterson

Quote:

Originally Posted by JDWalton

Now dont read too much into that and get into how they accomplish things different ways, I understand there two different devices, but my point on what they do is valid, and I was originaly trying to get at just how much added grip (roughly) people would think the drag launch kit would add, if there was already a properly installed and adjusted air bag. Reason being, to see if the added cost would be justified by performance.

No flame intended, but the kind of answer that you're looking for requires a little understanding of how the various approaches work, not just that they can work. Generally, drag racing manufacturer/vendor literature isn't complete enough, because its audience isn't oriented to the nuances of suspension function. So it's sometimes more difficult to get a handle on what's "known knowledge" as opposed to what's just a reprint of mass-market advertising copy. It really is possible to want things oversimplified to the point where a single, direct answer simply isn't possible.

You want help. I'm willing to try. But since it should be common knowledge that drag racing isn't my main automotive interest, you might be inclined to dismiss anything I post in a drag racing thread if I simply post it as a "just do it this way" kind of response without any explanation ("He's just an auotcrosser, what does he know about drag racing?"). Never mind that I need to go through a thought process first because even though I have some idea what's going on, it's not first and foremost from a drag racer's point of view.


A single air bag, in combination with the right spring rates, could be tuned via pressure to come up with some overall optimum combination of resisting roll and squat effects. A single air bag works indirectly by trading chassis roll off against the separate left and right squats, so it requires tuning. And since tuning is involved, you should expect that optimum tuning for one time and place may not be optimum under other conditions.

The big antiroll bar is easier to get right, since it directly opposes the driveshaft torque that leads to unequal left and right traction. The antiroll bar only needs for the endlink loads to be rigidly transferred back into main chassis structure, since any flexibility in the mounting structure reduces the effectiveness of the bar. That's a fabrication/installation factor that you should only have to address just the one time.

These two approaches are similar in that they oppose however much motion that the suspension geometry is going to let happen. The effectiveness of either is tied to chassis torsional stiffness.

Relo brackets attack the problem differently, in that they reduce the amount of motion that can happen, and the effectiveness of this mod is independent of chassis torsional stiffness. Think of this mod as being kind of "upstream" from the other two.

Does that at all help give your thinking better direction?


Norm

JDWalton

actualy its kind of insulting that you essentially came in here, continue to act like I must not have any understanding, explain how each work individually again, and didn't actually answer the question?

I understand that inertia wants to keep the weight of the car where its at, so as you accelerate and the car moves forward and the weight shifts to the rear.

I understand that is what makes the car squat.

I understand that whatever device you put in the back that fights squat (weather it be a air bag or torsion bar) is applying upward pressure (or resistance) as the rear trys to lower.

I understand that anytime you exert force the result is that a equal and opposite force is being applied.

I understand that the coefficient of the tire is not changing so the opposite force being applied by the device fighting the squat is transferring that force to the axle, applying more weight to the wheels, and giving you a net gain in traction.

I understand as changes in pressure and traction happen a air bag needs to be adjusted to provide proper launch.

I understand that the two devices I am talking about, do not achieve there advantage in the same way, they each have there own effect and means of transferring energy, but have a similar result on traction.

Now without breaking things down or trying to explain how anything else works, the question is:

If someone has a properly adjusted air bag, how much more traction do people think would generally be gained by adding a second device doing a similar job (like the BMR drag launch kit)? Do you think the cost would justify the reward?

Maybe this will help. I never asked for a explination of how these things work, I was looking for info from maybe.. someone who went through this series of mods or something similar. For example if someone came in and was like:
"Hey, I actualy have both these mods. When I had just my springs and airbag, I pulled 1.6 60 foot times, then I spent $500 on the drag launch kit, and it only got me to a 1.58 60 foot."

See thats a simple answer to my question, not assuming I don't know how some things work and try to explain everything. It requires no more explanation.

Doogie65

This thread on S197Forums should answer your question about what works.