Stock sway bars and road race suspension
 

I'm considering going back to stock sway bars due to my current classing and I wonder if any of you have tried it, did it work on track? I've got double adjustable shocks so I could compensate for some of the body roll with stiffer springs and shock adjustments.

You can put in stiffer springs to compensate but hopefully your tracks aren't bumpy.

You will have to run higher rate springs to achieve the same loaded wheel rate. If you had really stiff bars it might be a bigger number than you realize.

Shocks only control the "rate" of roll no different than they control the rate of suspension movement over bumps and whether the wheel stays in contact with the road surface or not. The amount of roll is determined by the total loaded wheel rate resulting from the combination of spring and swaybar together. I'm sure that you know this, but the way you worded the last part seems to imply to someone with less experience than yourself that shocks can be used to limit roll angle.

Thanks, Arca and Team. Yeah.. I know shocks won't limit total roll. I currently run the RB front sway and stock rear sway, combined with my current spring rates, it works beautifully.

My question is more about whether someone has faced this situation and, if so, is there any way to calculate a spring rate baseline based on current setup.

The one resource I checked online is the FCM calculator and, according to the numbers, I'd have to run 50% stiffer springs in the front.

That will get you in the general ballpark. It's not 100% accurate IMO.

Is there anything better out there? I am trying to avoid going to my friendly neighborhood university library and finding suspension design books!

You have to plot out the geometry relationships in order to calculate the theoretical forces. Either you measure all the suspension point positions, lengths, angles, etc. and model it on a 3-D suspension program or pay someone else to The site you mentioned has attempted to do so to some degree, but a few times using it didn't add up for me. Due to the time involved most people don't share the info for free. I'd say using that program is your best starting point.

Some people support a 'no sway bar' concept. I don't have any direct experience with it though. This vid is from the owner who put that modeling program together. It's a bit chatty, but might interest you if you have patience to watch it all the way through:



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sadly removing the bar you take the same hit as running an aftermarket one -- silly rules!

To me one of the keys to making this work outside of figuring out the right spring rate to compensate will be getting the stock bar and endlinks to work with the car being lowered and all that. NASA treats the endlinks as part of the swaybar currently. I've been lobbying against that for years to no avail.

The endlinks length when lowered is overplayed mostly, at least in this application. It' does have an impact, but a minor one IMO. Worst case it make s them slightly less effective (softer) which if you can't remove the bar without penalty is not necessarily a bad thing if that's the direction you want to head in.

In the vid above he actually suggest that a compromise between no-bars & stiff-bars is likely the best choice i.e. the OE bars in this case

I suspect in the end you will also need to adjust the rear springs as well. Even with the same bar the dynamics of softer front bar/stiffer front springs is likely to impact the balance some. Or at least that's my expectation ...

I didn't know if they would physically even work, you hear of in other platforms the endlinks breaking or bending when being run with an "upgraded" suspension - stiffer springs, lower ride height. Miata NA & NB most notably that I can recall as the biggest one. Some other platfroms the bar can flip over or otherwise do weird things.

If the RX8 is immune, sounds like a good 2pt savings to apply elsewhere.

I reviewed FCM's spreadsheet again. The data for RX8 is a bit bogus; for example, motion ratios are off. After using more accurate values, I can get a similar roll stiffness by bumping spring rates up approx 33%. I will need to get the shocks revalved, though.

Lol, the OE bars are so soft that the only way to bend an OE endlink is to install the rear bar upside down so that it jams against the subframe. I ran OE endlinks on bars much stiffer than OE without issue. If you can update to newer year RX8 bars the 2009+ R3 bars are the stiffest.

Yeah. I agree. I run OE end links with much stiffer ARB. Never had a problem with them.

Pretty much all us SoCal guys who are running the RX8 or NC Miata have switched back to the stock sway bar with pretty good results, including me. Just not worth the extra points as you can somewhat compensate with springs.

On the flip side, the 04-05 RX8 Auto trans 'red dot' swaybars are the softest

what spring rates are you guys using?