Why stiffer springs over stiffer swaybars? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 5 Old 01-04-2011, 09:39 PM Thread Starter
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Why stiffer springs over stiffer swaybars?

I don't see why its better to increase wheel rate over increasing roll resistance alone with bars.

I know that you will lift a wheel if you have too much roll stiffness in the front or rear, but if you balance between the front and rear, that shouldn't happen right? I would think you would want the softest springs you can get away with without bottoming out and to use stiffer bars to combat body roll. This way the tires will follow the irregularities in the road.

I'm not saying to run stock springs or softer than stock springs. I just think that a setup with say 450 front, 350 rear coil overs and stock bars may do better with bigger than stock bars (balanced of course) and slightly softer springs.

I'm just trying to wrap my head around what I've been reading on this site and on other sites.

Thanks for the help.

Ricky

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post #2 of 5 Old 01-04-2011, 10:19 PM
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Springs vs. bars is a religious argument...might as well throw damper theory and tuning in there, too, just to really get things started

You did hit on a fundamental difference, bars effect both sides of the suspension...one side gets forced down, the other side gets forced up. So, too big of bar hurts both turn in and the ability to put power down off turn. Also, bars don't do anything for squat or dive. Also, a bigger bar does actually increase spring rate, as soon as it encounters force to resist...if I'm saying it correctly. So, you're not "increasing roll resistance alone". Springs work independently of each other, with all the implications that brings with it.

It is an interesting topic, but I don't know that there is any real answer...but, I'm far from a suspension engineer or expert, so I'll just STFU and see what those that really know have to say.


Last edited by tigerdrvr; 01-04-2011 at 11:25 PM.
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post #3 of 5 Old 01-05-2011, 08:08 AM
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Stabilizer bars directly reduce the independence of the right and left wheels. As long as the pavement is smooth, this isn't a big concern, but smooth pavement is frequently not the case.

Another issue concerns damping. You have one shock per corner that has to damp both pure vertical chassis "heave" motion and chassis roll motion. With a big bar and soft springs you might well end up being overdamped in heave (with likely ride quality consequences) AND underdamped in roll (think about overshooting in roll and a longer time for a "set" to take).

NASCAR "big bar/soft spring" thinking aside, big bars and soft springs do tend to provide a softer ride in OE production cars, since OE cars tend to be underdamped below the point of best grip anyway.

I *think* you want to first choose your springs based on ride frequencies and "flat ride" behavior over the range of speeds that you anticipate mostly driving in. There are some rough guidelines for the frequencies, to which I'd add that with smoother pavement you can go higher with spring rates and ride frequencies (softer and lower frequencies for rougher pavement). Then choose the bars based on some target amount of roll per lateral g and overall front:rear balance of lateral load transfer. Tune your damping - I'm assuming at least single adjustables here - based on observing transient behavior. There's a Koni shock tuning procedure floating around that basically has you starting out full soft and adjusting upward.

There is another input to your choice of springs, and that is the amounts of anti-squat and anti-dive geometry that are present. With greater amounts of these "anti's", you'll need less spring to keep from having excessive vertical motion under acceleration/braking (or possible bottoming in the extreme). But don't go overboard with increasing the anti's solely to allow running softer springs, as this has some downsides if taken to extremes (think rear axle "brake hop" for one, unusually harsh front ride quality when braking on rough surfaces or over bumps for another).

There are many compromises.


Norm

Mine: '08 GT, 5MT, black/light graphite, un-Fstock (DD, occasional track day)
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Last edited by Norm Peterson; 01-05-2011 at 08:11 AM.
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post #4 of 5 Old 01-05-2011, 12:10 PM
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Here is a decent article on big bar/soft spring theory. The article relates to circle track asphalt racing, but the theories can be applied to road course setup as well.

http://www.longacreracing.com/articles/art.asp?ARTID=30

I recently had a long discussion with Mike Maier about this topic. He recently switched to the bb/ss setup and won another CP national championship this year. I'm not going to get into the specifics of the setup but he said the front grip and forward bite was better than ever. As stated earlier this is like religion, it's a theory just like the conventional setup is a theory. Both setups can be made to work very well, not as many people use the bb/ss setup so you will be on your own more so than if you choose to run a conventional setup.

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post #5 of 5 Old 01-06-2011, 09:35 AM Thread Starter
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Thanks all. Very informative.
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