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Please explain Roll Center......

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Fabman

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As I understand it, a roll center (RC) that is closer to the CG the vehicle will resist roll more, much like a stiffer spring. A RC that is farther away from the CG will make that axle softer.

Am I understanding this right or do I have it backwards ?????

That is correct.


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Norm Peterson

Corner Barstool Sitter
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Right as far as it goes.

Any "effective roll stiffness" from having a higher geometric RC comes in sooner than roll stiffness that comes from stiffer springs/bars/shocks/struts, and can be used to juggle transient handling a little.

In stick axle suspensions, rear axle roll steer is also somewhat dependent on the rear geo-RC height.


Norm
 
O.k. thanks.

I am trying to figure out why a Watts Link or this, http://store.kennybrown.com/product...-kit-heavy-duty-double-adjustable-panhard-bar , would require a reduction or complete loss of the rear sway bar.

If rear RC is moved away from the CG, effectively softening the rear, wouldn't removing the rear sway bar make it even softer? Or is the factory too stiff to start with???

Or am I over thinking things
 

Grant 302

basic and well known psychic
I saw and disagree with the video. At least the transcript. I don't think lowering the RC 'allows' the rear sway to be removed. But that it works with their 'system' changes. Without getting into the details, lowering a panhard connection points will change how the weight 'jacks' and transfers.

Side note: and that's very different for right and left turns. Consider how roll center migrates differently.
 
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A caveat here, while the roll center closer to the CG is usually a good thing, beware of going so low the R/C is below pavement level. In the earlier Fox body cars, lowering the car (especially the 99-04) will place the roll center below pavement level..this is why those cars run taller ball joints, bump steer extensions and whatever. Like everything else in suspensions too much of a good thing is usually bad.
Grant is correct in his statement, raising or lowering the PHB can hasve a dramatic effect, I used to mess around with a 250cc mini sprint, and that was ahuge factor in adjusting the suspension.
 

Fabman

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I saw and disagree with the video. At least the transcript. I don't think lowering the RC 'allows' the rear sway to be removed. But that it works with their 'system' changes. Without getting into the details, lowering a panhard connection points will change how the weight 'jacks' and transfers.

Side note: and that's very different for right and left turns. Consider how roll center migrates differently.
I've seen that video before and agree with you.
Additionally, if you watch his video on springs he says that he runs much higher spring rates than others which explains his strategy. Low roll center/no rear sway bar to let the rear end bite and higher spring rates to balance it. Same strategy I used so successfully in stock cars. Kind of an old school mentality. The trend has been towards softer setups in most circles for some time now. The advent of higher quality highly adjustable shocks has shifted thinking considerably.
 

Fabman

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I was watching the Kenny Brown video about his relocation kit. In it he says to remove the RSB.

Why???
It's a strategy, other prominent tuners do the same. It's supposed to make it feel less fidgety. However, to keep the neutral balance of the car much higher spring rates are needed to maintain a similar wheel rate. This works great with low powered cars because you are sacrificing forward bite with higher spring rates, but corner speed may be enhanced. The point of a rear sway bar is to let you run softer springs for traction and ride comfort while adding wheel rate in the corners to help limit body roll and tailor handling as the bar twists. High power cars will just spin the tires with that high of a rear spring rate so things are not so simple. The more power you make, the more complex and critical the interplay between the roll center, spring rate, shock rate and sway bar rates become. The less power you make, the more you can get away with.
 
if you watch his video on springs he says that he runs much higher spring rates than others which explains his strategy. Low roll center/no rear sway bar to let the rear end bite and higher spring rates to balance it. Same strategy I used so successfully in stock cars. Kind of an old school mentality.

So, we are back to running a bit smaller RSB.....
 

Fabman

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So, we are back to running a bit smaller RSB.....
Its like soup....you season to taste.
Most like the smaller rear bar, some prefer no bar.
I drove a spec mustang at Sonoma last year with a super high roll center, no rear bar and super stiff rear springs. While it was a little loose for my taste, the regular driver was able to win the championship with it so it was just right for him. Spec Mustangs also make about 300 Horsepower so they get away with it. Add 100 hp and it would be a whole lot harder to hook up.
 

Norm Peterson

Corner Barstool Sitter
939
712
Exp. Type
HPDE
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a few miles east of Philly
Here's a link to it on YouTube, should work better:
It sure does, and thanks.

Off the top of my head, he may be getting 'jacking' confused with roll. At best, maybe there's enough change in axle roll steer going on to compensate a little for having two effects both moving the TLLTD to a more forward biased condition.


Grant - I could get to the videos tab, but when I click on Part 5 all I get is a black popup box that never does anything at all. I can even click on the 'Part 6 of 8' or whatever and make the box blink and the 'part' change, with no video whatsoever.


Norm
 

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