Running no rear sway bar on track?

Mark Aubele said:

315s all around. Konis with GC coilover kit. Running a bit more spacer up front that necessary. 18x10.5s 7.75" BS 3/4" spacer up front.

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That looks awesome!
I'm on 10" Apex wheels. Really good strong and light wheels, but 10" is the biggest they make so I am limited to a 275 or 285 tire.

Fabman said:

Just sounds like I would be pushing the limits going in with no place to go....

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That's not necessarily true. Even if you were approaching the limits with the dampers as they are, you can get Koni to revalve them to something more suitable to your application. I don't know what the cost of doing that might be, but I'd bet the total cash outlay will still wind up being less than the other options.

However, that said, I've no idea how well the Koni internals will hold up under the increased stress.

Frankly, I'd call Koni and ask about this. Find out how much it would cost to revalve your shocks to better handle increased spring rates (I'm sure you'd have to specify a rate range so they'd know how to valve them), what the turnaround time would be, what you could expect the life expectancy to be, what it would do to the warranty (you'd be sending it to them for the revalve, so the warranty might well remain intact), etc.

There's no money spent until you actually execute on a decision, so it won't hurt to get the info you need, and it'll help you understand your options better.

I have been brutal to these Konis, and they have held up well. As KCBrown says (great posts and info, thank you for the tech), run the Konis as is. Revalve if needed. Mine worked "fine" with 550/300 rates. Sometimes 95% of the way there for 400 dollars is better than 100% for 5k. I guarantee you will see a massive improvement in performance with the simple GC kit if the ride height is kept within reason, and the stiff springs will help keep the car from bottoming, which is what kills the Konis. The ones that get blown are always excessively lowered with way too soft of a spring.

Gentlemen, you have talked me into it....thanks for all the information.
Now if I could just get some help programming my DVR...

This all boils down to one thing. What is the roll stiffness distribution of the suspension? That will determine if you want to remove the rear swaybar or not.

Buried in this thread someone took their front spring rate and added it to the front swaybar rate to come up with the front roll stiffness. This is not correct. Swaybar rates are virtually always quoted as the force required to deflect the end of one arm 1" when the other arm is held static. That only represents 0.5" of roll. If you want to add this swaybar stiffness to the front wheel rate from the springs, you need to double the swaybar rate first.

Jack Hidley said:

Buried in this thread someone took their front spring rate and added it to the front swaybar rate to come up with the front roll stiffness. This is not correct. Swaybar rates are virtually always quoted as the force required to deflect the end of one arm 1" when the other arm is held static. That only represents 0.5" of roll. If you want to add this swaybar stiffness to the front wheel rate from the springs, you need to double the swaybar rate first.

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That's the way I used to work a bar rate into TLLTD calcs, and that's still the way I'd do it for some purposes. But I've found that approach can give unreasonably high roll stiffness results - when commonly available bar rates plus springs in the 250 lb/in ballpark end up giving you roll rates below 1°/g, something is more obviously amiss than when you get ~3°/g with all stock rate stuff.

So more recently I've been working with bar rates reflected directly to in-lbs/deg referenced to either the chassis pickups or the "bend points" at the ends of the torsional section. It's still based on 0.5" (relative) bar end deflection on either side. And this approach has been in far better agreement with the K&C data that C/D published a while back for the Mustang (within 10% of the roll rate and within 2% of the roll stiffness distribution) with no attempt to tweak the inputs or formulas to make the results look good).


Norm

Well, I called Ground Control (in December) and talked to a guy who said his Boss runs a Mustang and that he would find out exactly what the best setup was.....and never called me back.
I also called Koni to find out how much spring the yellows were good for. And they never called me back.
So I sent an email to Cortex on a saturday night and got a reply the next day. Sunday! Some customer service felt good right about then.
Long story short, I ordered the Cortex/JRI track package and I feel pretty good about it.

Stay tuned.

Mark Aubele said:

...The ones that get blown are always excessively lowered with way too soft of a spring.

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Funny how often that part of the story gets left out. 2-1/2 + yrs on mine. 43 plus track and autocross days (and counting). Nothing but good experiences here.

Daily driver and crap roads here means modest lowering and mild (by track terms) springs. Konis are more that up to that dampening task. Might make different choices for a dedicated track machine of course, but that's not where I'm at, and the full tilt coilover setup would be 2-3 years tire budget.

My times on track and autocross compare very well. Sure hisses off the koni haters. Fortunately, I'm not above a little smack talk. Sometimes give it, sometimes get it.

El_Tortuga said:

My times on track and autocross compare very well. Sure hisses off the koni haters. Fortunately, I'm not above a little smack talk. Sometimes give it, sometimes get it.

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They can also be revalved. I will be running between a 700-800lb spring up front. Will post shock dyno when I get them back in a couple weeks. Not sure what I will run in the rear, will likely go back to 300 from 250 but I will try the 250 first.

Lee Grimes is the man to talk to at Koni NA. Answered my call and spent 20+ minutes with me discussing my options with my desire to go up in spring rate. Didn't try to upsell me, and answered every question I had, even though I ended up going through Truechoice for the revalve, Koni was a 8 week wait.

Norm,

Both techniques should give the same results.

Not doubling the swaybar stiffness numbers is sort of like inventorying eggs by counting 10 of them in each carton to compensate for the fact that 2 out of every dozen get broken.

To get numbers that agree with data from a K/C rig you are going to have to measure everything very accurately. In my experience the differences are all the results of tolerance stackup in the analysis and not taking into account items that are not easy to find values for. Without putting the swaybars stiffness in parallel with the frame horns stiffness, you will never be even close for instance. The front swaybar mounts are cantilevered as far from the strut towers as possible off in space.

Another thing to consider is bushing stiffness. As an example, on the rear of the S550, the bushings create more than 20% of the ride rate.

I agree, both approaches should end up with much better agreement, but then I remembered a discussion elsewhere where the question of what to do with the spring stiffness and the bar stiffness on the inboard side of the car. So I went back to RCVD, where the equations work with the roll stiffness of the bar (units of moment per unit roll) added to the KwT^2 for the springs rather than end stiffnesses reflected to the wheels and added to the Kw from the springs. I still don't know where the disconnect is. But I do have a clear memory of installing a front bar on a car that came OE with no bars at all . . . and having a decided feeling with that as the only mod that the entire front end of the car was being held up higher through the turns, not just the outside front.

Off the top of my head, I was using the C/D-listed wheel rates which if taken from the K&C session should include bushing stiffnesses, and the stiffness for a 24mm front bar (forget which rear bar). The model allows for inputting finite chassis torsional stiffness and vertical tire spring rates (typically between 1000 and 2000 lb/in).


Norm

And there it is....ordered on Sunday, Delivered on Tuesday, will Install this Sunday. Can't wait.

Fabman said:

And there it is....ordered on Sunday, Delivered on Tuesday, will Install this Sunday. Can't wait.

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After the install, can you kindly show us a pix of both the front + back?

Here's the rear.
I didn't take pictures of the front, but I will later and post.

Looks great

Can we see the rear at ride height? Curious about bump travel.

csamsh said:

Can we see the rear at ride height? Curious about bump travel.

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Weeeelllll....I'll tell ya. The jury is still out on that one.
The directions that came with the kit call for a measurement that makes the suspension angles all happy but the car looks a little 4WD if you know what I mean.
The height given in the kit is labeled "street".
Its a measurement from a spot on the chassis as measured from the ground. This does not take in consideration the height of the tires.
So a car with 24.5" tall tires and a car with 27.5" tires will look very different to the suspension.
At this point I have everything installed and close to ride height, but I left the final setup and alignment for next weekend.
Ima need to think about this one a little bit before I move forward.

What I CAN tell you is that on my 06 s197 I have 27" to the top of the wheel well arch in front and 27.5 in back and there is 2" of wheel gap in front and 3" in back.
According to the paperwork I have this is still way too low.

See that pic of my car in the sig?
It looks nothing like that now. :-/

What size tires is that measurement for?