sway bars....

travisjb

Hopefully Robert (redline) continues to weigh in, he's definitely THE EXPERT in this area... his shop has 2-3 porsche cup cars in it on any given day and he spent years as a mech with PMNA

My thought is that it sounds like you need to work the suspension, this likely isn't a problem with tire pressure based on your cold psi... more negative camber plus stiffen it up... spc/spl control arms plus hotchkis/stillen bars should do the trick... if you decide you want more, then stiffer springs or coilovers... or just keep burning through tires !

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2009 370Z #104
*For Sale*

travisjb

Phim, your logic is sound... I've made that same argument on this board... It's called an asymmetric setup, and it is used on occassion... whiteline has collected data on it here http://www.whiteline.com.au/articles...metric_adj.pdf ... they concluded that using an asymmetric setting will result in asymmetric anti-sway forces (go figure!)... it's a nuance

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2009 370Z #104
*For Sale*

ChrisSlicks

Yes the resulting bar force is linear and equal on both sides as you both described. In order to have different forces on each side you would have to weld the center of the bar to the frame to prevent the forces being spread out the length of the bar.

Phimosis

The asymmetry is really only in the position where the end links are bolted to the sway bar, not in the forces applied to the end links. Because the sway bar and end links are gliding in lubricated bushings, the forces applied to each end link at the sway bar end of the end link are equal. To get to the really technical nitty gritty, the force applied to the sway bar end of the end links will be equal, but because the end links will be at a slightly different angles to the lower control arm, the forces are slightly asymmetric based on the angle of the end link in relation to the lower control arm. Ideally, the end link will be perpendicular (90 degrees) to the lower control arm and the control arm will see 100% of the force that the sway bar applies on the end link. If the end link is not perpendicular to the lower control arm, the force on the lower control arm will be (force applied to end link) X (sin theta angle). So if one end link is perpendicular to the lower control arm on the "long setting" and applying 1000kg force, and the other end link is on the "short setting" at theta angle 88 degrees, it will be applying 999.3908 kg force, or 99.94% as much as at the other end, which I believe is negligible.

If that difference is not negligible due to the asymmetry, then the Stillen bar actually has 4 different settings, not 3 as they claim. I would go with calling it a "3 setting" sway bar.

With my usual disclaimer, I have taken calculus based physics, but I was a biology major. If any engineers want to correct my math, please do. It's been 15 years since I have done these types of calculations.

-Phim

travisjb

Chris, that makes sense from a static forces perspective, but would you think about it differently in terms of the instantaneous forces applied before the load can be transferred across the bar? ie whiteline said an asymmetric setup produces asymmetric forces, and they posted data to back it up... regardless, prob all nets out to very little difference, huh?

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2009 370Z #104
*For Sale*

travisjb

I took plenty of phsyics and calculus in engineering school, but have NO INTEREST in correcting your math ! I think you're right, there's prob a difference in angle... forces are placed upon the wheel hubs, that's what the anti-sway bars are for... so, I suspect there is a force difference for asymmetric setups that has nothing to do with the angle at the hub/bar, and that this force difference across sides exists momentarily until the load is fully absorbed by the bar as torsion deflection... at that point, asymmetry is a non-issue... before that point, asymmetry may be an issue, but the thing I don't know is for how much time and does that translate into anything the driver would notice... honestly, we can dispense with all this discussion and just try it !! and of course, worth going back to whiteline and asking them what they found if you're really curious

__________________
2009 370Z #104
*For Sale*

ChrisSlicks

I don't think instantaneous forces are a factor here, those would be so brief they would be unmeasurable and definitely not something the bar is going to have any effect on. The bar is designed to respond to continuous loads not micro bumps.

Now that I've thought about it a little more the asymmetry has more to do with the length of the lever arm being different on each end. The length of the bar will act as a single spring, however because the length of the lever is different on each side the resulting multiplier will be slightly different. So although the spring tension is equal across the length, the lever length twisting the bar is different.

arcticreaver

could someone tell him which settings would be good for street use and some canyon runs? for both hotchkis and stillen?

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Phimosis

I like it stiff. I have the Stillen bar on the stiffest setting and my coilovers are at 10, with 0 being the stiffest, 20 being similar to the stock shocks and 32 being the softest. I tried the coil overs at 8, but I was just too choppy for street use and started to "skitter" around over expansion joints and whatnot.

I tell you about the coil overs because the Stillen bar on the stiffest setting may not work well with your shocks. You just have to try it out and see if it feels better or worse to you.

ChrisSlicks

I'll be installing the Hotchkis sway bars on the stock suspension this weekend. I'll try the full stiff setting first and let you know how it is.

blackbird

Just an FYI but he NISMO Coils, Shocks and sway bars work very nicely. Tightens up ride but not harsh.