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oh, it was my fault steve, i thought this was no holds barred competition car. I am glad you showed why manufacturers do it the way they do though.

My cars runs SM2, should I look at stiffer rates than 550/400 in the area of 600/450?

awesome write up
 

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You bastards (read:mods) better make this a sticky asap. Im sure steve-o will not be or have the time to do this again. Thanks. ;)


steveo, what would be the needed calculation changes i would need to make if i was to delete the front are rear swaybars entirely?
 

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Thanks :) Maybe a reminder too?

I hope to have another installment this week. I was busy the last two weeks working on the DP car getting ready for the Atlanta Tour, a customer car and a business project.

-Steve
 

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Discussion Starter #25
XHead said:
Thanks :) Maybe a reminder too?

I hope to have another installment this week. I was busy the last two weeks working on the DP car getting ready for the Atlanta Tour, a customer car and a business project.

-Steve
Why I would never :p

Nah I've been busy also. Just had a new Exhaust made and need to figure out the rest of the oil leaks in the car.
 

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Discussion Starter #26
Awaiting the next installement if you have time.

Kinda on the edge of my seat to understand how where the sway bars come in to the equation if you are not using them to tune the wheel rate exactly.

I've figured out my wheel rate to be 600 front and 450 rear. Right now I have 250lb springs on the front with 350lb sways and 400lb rear springs with a 35lb rear bar. I'm getting a pretty good balance with the car, although I have not set the ride heights as you have mentioned in your previous posts (I would have to rebuild my suspension for that and get new springs.....which I'm still don't have the info on what they should be)

Anyway, not forcing you, I know you are busy. Friendly reminder and all :)
 

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Well, I may be able to do another installment this week. I have been very busy the last few weeks working on a new business venture. Things may be calming down some this week. Also, my girlfriend Terrie is going to be out the later part of the week and that will free me up some too.

I will endeavor to get it done and posted.

-Steve
 

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Mica,
Will hint that you are a good student. Based on what you and I have discovered, with Steve's insight you are on the right path. Are you thinking to use the stock OEM struts, or modify them? Consider ride height, strut travel, clearance issues (tire diameters) etc. I know my car is very close to being optimum (finally!) based on what Steve's been talking about. Once the coilovers/struts are in just
try it without the sway bars first....
 

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Installment #4:

Now that we understand the function of the springs and how they interact with the body to determine ride quality and body roll we can now directly address the swaybars. To achieve our target body roll and roll ratio we have chosen specific wheel rates. However, the rates we have chosen would result in a very stiff ride if we used only springs to achieve that wheel rate. To soften the ride we need to lower the spring rates, especially in the front (to achieve a positive favored speed) however, that will upset our chosen roll ratio so we add back wheel rate by supplementing spring rate with swaybar rate.

From installment #2 we had chosen 550 lbs/in front and 400 lbs/in rear spring rates. Its easy to now choose a front spring rate that will produce a more comfortable ride. Say 300 lbs/in front springs would give us a positive favored speed and move the center of suspension closer to the CG of the car, just aft of the center point between the two axles. We can then add back the spring rate by installing a swaybar with a rate of 250 lbs/in.

250 lbs/in front bar + 300 lbs/in spring = total rate of 550 lbs/in.

That looks pretty easy. However, its hard to find an off the shelf swaybar that has exactly the rate you want. In reality, unless you want to fabricate a custom bar every time you want to test a different setup, you need to calculate the rates of the available bars and then determine how much spring rate you need to achieve the desired total rate. So lets say you measure your existing swaybar and find it has a rate of 200 lbs/in. The spring rate you would want is determined by subtracting the existing bar rate from the target spring rate.

550 lbs/in target rate ? 200 lbs/in bar = 350 lbs/in springs.

Easy enough. But we have a problem here. Swaybars are not the dynamic equivalent of springs. A swaybar transfers load from the inside tire to the outside tire and thus reduce mechanical grip as they add spring rate. And the effect is not linear. The stiffer the bar in comparison to the springs, the greater the effect (loss of mechanical grip). To give an example of the effect, if we set our proposed STS2 car up using the target data we have assumed above using the target spring rates without any swaybar, the car should have good balance. However, if we achieved that same target spring rate using a front swaybar, the car would tend to understeer more than if we used only springs and no swaybar. And the greater percentage of the total front spring rate the bar accounted for, the more the car would understeer. I noted as much early in the thread.

We now must choose how much bar we want to use for our final setup. As the reader may know, I don?t use swaybars on my DP car. Nor did I use swaybars on my previous racecar, a DSP X1/9. For me it is far easier to manage the setup of the car without swaybars. I also prefer the feel of the car without swaybars. It has long been my thought that; because a swaybar reduces mechanical grip, why would you want to put anything on the car that reduces mechanical grip?

With this simple method, it is easy to compare the effect of the front bar by comparing the same total spring rate using just springs and no front bar to the same total spring rate incorporating a front bar. I have done extensive testing and have proven to my own satisfaction that the theory is in fact accurate. The same total front spring rate achieved using a front swaybar will produce more understeer than the same total front spring rate achieved using springs only. In addition, the effect of the front bar changes based on the level of grip the surface offers. As a result, the car does not have consistent balance from surface to surface or even from run to run as the tires heat up from and the surface cleans and heat up throughout the day. I have found that my no-swaybar setup is very consistent on different surfaces and conditions seldom if ever requiring any changes to setup. At most, a pound or two of air pressure is all that is needed to tune the balance even in the most extreme of conditions. In fact, I don?t even change the setup for rain. All I have to do is bolt on the rain tires and the car is fine.

If one chooses to use a front swaybar, the effect resulting from the loss of mechanical grip will have to be accounted for by softening the front springs enough to bring the balance back to neutral. Choosing the amount of swaybar to use is now easy and dependant on driver taste. If the driver prefers a smoother/softer ride, use a very stiff front swaybar and subtract the front bar rate from the total spring rate to determine the required front spring rate. Testing can then determine how much less spring rate is necessary to bring the handling balance back to neutral. One could also compromise and use a very soft front bar, thus minimizing the loss of mechanical grip.

-Steve
 

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Thank you Steve. Good to know my thinking was going in the right direction at least.
So, to do a noobish recap - You can use sway bars to compensate for the additional roll-rate you want without using super-stiff springs, but at the cost of mechanical grip at that end of the car. In this regard, swaybars help keep the suspension geometry closer to the sweet spot, but loads up the tire that is already doing the hard work. Compromises, compromises.

Did I get that right?
 

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Discussion Starter #33
truebluemr2 said:
Mica,
Will hint that you are a good student. Based on what you and I have discovered, with Steve's insight you are on the right path. Are you thinking to use the stock OEM struts, or modify them? Consider ride height, strut travel, clearance issues (tire diameters) etc. I know my car is very close to being optimum (finally!) based on what Steve's been talking about. Once the coilovers/struts are in just
try it without the sway bars first....
I am using the stock oem Strut tubes with Koni's. Now I might do something with them if they will not allow me full control over my suspension though.

I still need to cut the perches off of them...been to lazy and had too many cars to work on :)


Yeah I have been on the ball with the whole sway bar thing. This might be the time to let the sway bars go and go for a spring only setup which would make it easier.
 

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thirdvector said:
In this regard, swaybars help keep the suspension geometry closer to the sweet spot, but loads up the tire that is already doing the hard work. Compromises, compromises.

Did I get that right?
I think you swapped terms. Try this instead:

A swaybar (especially a front swaybar) lets you keep the front spring rates down and thus keep the ride frequencies closer to the "sweet spot".

The car will roll close to the same amount for a given spring/bar rate regardless of how the rates are divided between spring and bar.

The next installment will cover some of my testing results and throw you a curve. :smile:

-Steve
 

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XHead said:
I think you swapped terms. Try this instead:

A swaybar (especially a front swaybar) lets you keep the front spring rates down and thus keep the ride frequencies closer to the "sweet spot".

The car will roll close to the same amount for a given spring/bar rate regardless of how the rates are divided between spring and bar.

The next installment will cover some of my testing results and throw you a curve. :smile:
-Steve
Im thinking that you found out that you needed more spring that what your calculations came up with.
 

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verno-dub said:
Im thinking that you found out that you needed more spring that what your calculations came up with.
I'm "guessing" that his testing shows the car handles most neutrally when the (total) front spring rates are 150% of the rear spring rates.
 

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Discussion Starter #40
XHead said:
Who the ____ is that guy???

I just thought it would be fun dropping in a little teaser. How about this:

Remember this number: 150%

-Steve
M Night Shalalmalayalaman. 6th Sense, Unbreakable and so on :)

There is always a twist in his movies.
 
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