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Sway-bar? or Lack of sway-bar ?

Old 09-17-02, 03:10 PM
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Lightbulb Sway-bar? or Lack of sway-bar ?

This question is refering to the car in the sig. In the interest of loosing more weight on my car and eliminating one more tuning variable - Is there a way to calculate the needed increased spring rate to keep the body roll the same if I were to remove the sway-bars from the racecar? The increase I'm refering to would be the amount needed to keep the car at the same fairly flat cornering ability with the big sway bars but accomplish that with stiffer coil spring rates. There are a few good National level autocross cars running without sway-bars but some of those people are just unreachable. Either they don't want to share info. or they are on the other side of the USA. I was just curious as I'm trying to plan the next year or two for my cars upgrades and this could be part of the winter rebuild stuff for 2003.
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Old 09-18-02, 09:34 AM
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Yes, it is entirely possible to do what you are asking. And there are two ways to accomplish it. The (possibly) more expensive way is to just keep trying springs until you get what you like. The other way involves a lot of math. You can probably find what your looking for in Milliken & Milliken's "Race Car Vehicle Dynamics". The problem is that even after you "calculate" what you need... it'll probably be wrong, since theoretical seldom equals real life. So you end up spending money on multiple sets of springs anyway.
It will probably be less painful (mentally, and financially) if you just bought an adjustable sway bar and learned to tune the car through trial and error. I'm sure there are some experienced people (autocrossers) in your area that would be wiling to help you sort the car.
Good luck.
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Old 09-18-02, 10:25 AM
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I'm just trying to plan right now. I'll look for that book and start playing with some of the formula's as see what I get. Like I said this is just in the planning/thinking stage right now. If I decide to go that route it will be during a major change in the car. I'll be adding a roll cage and larger racing slicks to the car and possibly a ported engine so I would be basically starting over anyway. The one experience autocrosser I know that runs without sway-bars is not to free with information on his car but his car is a rear engine car so what works for hime maynot work for me. I'll ask but I'm not expecting alot especially if he thinks my car will be faster than his even thou we run in a different classes.
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Old 09-18-02, 12:08 PM
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It just seems to me to be the wrong approach for an auto-x car. For a road race car, sure, since most corners are steady state corners, but in an auto-x, transitions are so much more important, and traction is at a premium with such slow speeds and big power. I'd think a soft spring, stiff swaybar setup would be more ideal for an auto-x course.

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Old 09-18-02, 03:49 PM
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Your also right Silkworm. I've seen competitive cars setup both ways but more of them with sway-bars. I'll probably end up with something like the BP winner at Nationals this year(and last year). I could duplicate his setup easy enough, its the learning to drive better that is the harder more time consuming part. I'm just exploring all possibilities since I have plenty of time to prepare for them.
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Old 09-20-02, 01:50 PM
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Originally posted by Silkworm
... but in an auto-x, transitions are so much more important, and traction is at a premium with such slow speeds and big power. I'd think a soft spring, stiff swaybar setup would be more ideal for an auto-x course.
I'm going to have to disagree with you here. A stiff sway bar setup will try to lift the inside tire (front or rear), resulting in loss of traction. If you run stiff springs, the car will still transition very quickly, maintain proper camber, and not try to pull a tire off the ground. My opinion is to only use the sway bars to fine tune the balance front to rear. That's why I plan on getting adjustable sway bars for both ends.
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Old 09-20-02, 02:13 PM
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Travis R - Your version is similiar to some of the top level autocross guys. Get your spring rates close and fine tune with a smaller sway-bar. Spring rates are fairly stiff 500+ on the front.

Last edited by FPrep2ndGenRX7; 09-20-02 at 02:16 PM.
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Old 09-20-02, 02:40 PM
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This is VERY interesting. I just put a 20B in my FC and the sway bar doesn't fit. Curently, I'm running the stock 13 year old suspension, so that is on my list of "to do in the near future" mods. If I can tune the front springs to behave without a swaybar, that would be one less headache. I will not be autocrossing this car. It is mostly a street car with a 2nd home on the drag strip, so turning is NOT a major concern, but what is an RX7 that can't turn? exactly....
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Old 09-23-02, 10:41 PM
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(*matt dons his convenient, portable, fire-retardant suit.. *)

Originally posted by Kurgan
but what is an RX7 that can't turn?
Hmm... a rotary powered mustang?!
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