Attached is my current setup compared to the stock Sport Suspension.

Current alignment values for those interested are:

Front caster: -5.5 degrees
Front camber: -1.5 degrees
Front toe: -1/8" total (toe out)

Rear camber: -1.5 degrees
Rear toe: +1/8" total (toe in)

Current impressions is that the car is very stable in steady state sweepers, and is easily modulated between understeer and oversteer with steering input or throttle. The car pushes with understeer in lower speed fast transitions (autocross), but is very neutral in long sweepers.

Future plans are to increase front camber to -2.0, and probably increase rear roll stiffness for autocross by using the stiffer position on the rear bar.

I am also on stock shocks, which will also explain the difference in handling in steady state and transient responses. D-Specs are on my Xmas list this year.

Thanks again for sharing the spreadsheet.

Wow, that was fast work!

it bodes well for the women-folk that speed is one of my strengths

So after having some fun on track over Saturday and Sunday, here are my findings:

Setup 1A (66.7% calculated FRC): Slight understeer, front tires heat more than the rears leading to more understeer once the tires have gone over their optimum temps. The rear was well planted exiting corners under full throttle. The car would push slightly to start with and then more noticeably as the tires overheated.

Setup 1B (61.7% calculated FRC): Neutral to very slight oversteer. Rears heat up slightly quicker than fronts. Once the tires had gone over their optimum temps the rears would drift a few % more than the fronts exiting a corner full throttle in 3rd gear.

Based on some rough tire temp measurements (used a probe in the garage after a session) I settled on hot pressures of around 32psi rear, 36.5psi front. Rear camber seemed about right. Front could have used a little more camber, but is already maxed out (hence the higher pressures to try and equalize tire temps). This is with a 14inch ride height. 17/255/40 Direzza Z2 tires.

Conclusion: Setup 1A felt 75% away from perfect, while 1B felt 25% away in the opposite direction. I need to try a stock miata (softer) rear bar, or more front camber/lower ride height). I'd really like to run with a softer front bar, and no rear but have not found a front bar with the appropriate stiffness.

Results may vary based on track, conditions, driver, and mental state. I'm also not really sure where I got the spring MR's from (Paimon?), nor how accurate they are, but it's all relative, so you can compare results to mine if you use the same ones.

Kudos to Shaikh at FCM for a really nice setup and being almost exactly spot on with his predictions.

Played around with the spreadsheet some more having realized my earlier error (now edited out in the previous post)

So I just got back from Thunderhill last weekend where I tried a 13.5 inch ride height to give me more effective front (and rear) camber, and the front bar on full stiff with the stock rear bar. This gave me what I think was an ideal balance. I could trail brake with confidence, and get on the throttle early without suffering too much understeer. It felt almost perfectly neutral mid-corner. Massive amounts of fun :)

Only problem is 13.5 inches is too low to work for me on the street. So I have raised it up to 13.75. Will see how it does with that next time and then go back and get the alignment (toe and rear camber) fine tuned...

too bad there are setup values you can't edit that are different between the RX8 and MX5, there's a reason he has separate calculators in the first place

excuse me why I go have a facepalm moment ...

Unlike the RX8 spreadsheet, all the input fields I see on the NC spreadsheet can be edited, even the unit conversion values. What am I missing?

any feedback on hotchkis bars? thay are on sale, had them on my Audi S4 and they were good. Reading their specs and rear bar looks very stiff? These would go with S2 with stock suspension...

Front Sway Bar: 110, 150 and 195 percent stiffer than the stock sway bar
Rear Sway Bar:195, 250 and 340 percent stiffer than the stock sway bar!?

They're just swaybars. Some people have chosen the NC Miata bars instead due to them being less stiff. Ultimately it comes down to your preference between spring rate vs sway bar rate.

I installed the front Progress Miata bar on my RX-8 GT Saturday afternoon. It is currently mounted to Whiteline adjustable end links and is set to its softest setting. The rear bar is a stock orange dot. I am running on Bilstein PSS9 coilovers, and ride height is set to roughly 13.75" [car is corner balanced].

What I am trying to achieve is to dial out a tiny bit of oversteer to make the car more neutral. Most people would consider it to be pretty neutral already, but there is a little bit too much oversteer for my taste, which affects my confidence at times on some tracks.

I have a track night tomorrow and will report back on how it goes.

One installation note: the tabs are so long, that the bar cannot be installed the Racing Beat way. The undertray has to be removed.

https://cimg8.ibsrv.net/gimg/www.rx8...b605bfb8fa.jpg

Success! Set on its softest setting, the bar effectively eliminated the oversteer I wanted to remove, and the car was more neutral yesterday. It is still biased slightly toward oversteer, therefore I had no problems with pushing, or with getting the rear to rotate when I wanted it to. The only time I found myself battling oversteer was when the tires became greasy from the heat. Additionally, turn-in is more crisp, which gives me more confidence in the car. Really liking this bar so far. My next track day is in a little over 2 weeks. I'll report back again after that one.

I am about to pull the trigger on set of Hotchkis bars, but I am on stock suspension which proved to be quite neutral when I was on Summit Point Shenandoah track which is quite twisty and technical. Car rotated very nicely, but it did have quite a bit of the lean in the tight corners..my knees were hurting from bracing :-)

The Progress bar on it's softest setting should be stiffer than the R3 front bar.

Not sure what the RB way is, but all you have to do is drop off the lower radiator mounts as I recall, maybe the front undercover too. Been a while since I last did one, maybe 6 years or so.

^ Then it seems I needed a touch more than the R3 bar I was considering.

The RB way is to remove the rearmost undertray screws and push against the undertray to squeeze the old one out and the new one in without having to remove the undertray or the lower radiator mounts. I was able to fish the old one out that way and fish the new one in, but I could not get the tabs to clear the tie rod ends without removing the undertray. Really wish my new radiator had arrived last Friday like it was supposed to, so I could do it all at once...

Mazda actually designs their suspensions to use body roll to an advantage. The roll vs. the bump stops is engineered in. It is weird, but it is true. I read an article featuring an interview with Randy Pobst some years back in which he discusses this from a driver's point of view. The thrust is that it takes some adjustment, but is more than fine thereafter. He is always skeptical, but always convinced in short order.

My limited experience says that many, if not most, adjustments to Mazda suspensions actually cause more problems than they solve. Judge the performance of yourself and your car by your lap times--not by the amount of body roll you experience.

"Mazda actually designs their suspensions to use body roll to an advantage. The roll vs. the bump stops is engineered in."
This is true to some extent and in the circumstances that you can encounter on the street with street tires, track is different environment all together especially when run with r-comps. Then excessive body roll reduces your contact patch and increases weight transfers which takes your grip away and reduces cornering speeds....

True. R comps are a whole different ballgame.

Installed Hotchkis sways last night at the local Mazda Club Tech session. Much easier to do on the lift :-), however that plastic under-tray was still bitch to take off. Took me more time to R&R the under-tray then then sway bar! didn't have to undo radiator support either. I set both bars on the middle setting, didn't have chance to really push the car on the way home but there was noticeable improvement in the turn in, steering response and almost no lean in the corners :-)

Changed transmission fluid to redline mt-90 as well, but didn't take sample since I ran out of the UOA sample bottles. Car only has 29K miles and there was lot of crap on the magnetic plug with stock fluid...

Groovy. Let us know how it handles on the track. Hotchkis makes a huge bar for this car.

How do you like the MT-90? I felt like I had a whole new transmission when I changed mine with it at 20K.

What advice to readers have for sway bar changes for a supercharger or turbo conversion, involving as they do an increase in weight over the front wheels?

Does anyone know the diameter of the stock red dot automatic rear swaybar?

Pretty sure for the S1 cars that it's the same OD as the rear sport yellow dot bar, just slightly thinner wall thickness

Been a while though ...

You can't edit the wheelbase, which the RX8 wheelbase is over 17" longer (19.3 %) than the NC

That makes all your numbers fubar ...

Gr8 thread

My set up uses stock sway bars and I am running front 504 (9) and rear 336 (6) spring rates.


The front roll couple (FRC) is 62.3% and I consider this to be almost perfect. I need to run just a hair less damping in the rear then the front is dial it in where I like it. you can run the damping even clicks front and rear and the car is basically neutral.


I concur with your FRC numbers.

You guys love to quote numbers ...

how big is the difference after installing rear bars? been looking into it, is it worth sacrificing the trunk for it?

:dunno: are you thinking about a strut bar? The sway bar goes under the car. If you have to ask, you don't need an upgraded one.