New Sway Bar Option and Sway Bar Summary
 

Just in time, I found a new offering in a sway bar set for the RX-8: Progress Tech for the 06+ Miata MX-5. AFIK, this was developed through Good-Win Racing: Progress Technologies MX5 FRONT and REAR AntiSway Bar Combo! for MX5 2006-2013 The bars, while not (yet) listed on PT's website ( www.progressauto.com ), a Google search with the part number and the word 'Miata' will give several other vendors.

I wanted a sway bar set in the "moderate" range of stiffness, but adjustable enough to take it stiffer, as needed. Something like the Whitelines, but better made ends and with tabs on the bar to prevent it sliding sideways. Eibachs were also a possibility, but have been discontinued as of June 2010.

Here's a table I compiled showing the range of sway options and where the new bars fit in that scheme. Left out are the softer, "red dot", bars that came on the automatic tranny cars sold in the USA and the Speedsource bars made for Mazda racing insiders. The stiffness values are assembled from the forum and company specs and are at best, estimates. They are listed by increasing stiffness (approximately) and where values of stiffness are given, it's relative to the stock models with sport suspension. Bars in the list are for the RX-8, unless "Miata" is specified. Weight is shown in parenthesis, if known.

Front Bars:

Stock Sport “Yellow Dot” 26.5 mm, 3.5 mm wall (6.3 lbs) = 1 and 1.2 redrilled
R3 “Orange Dot” 21.3 mm solid, fixed = 1.2 (guess)
Mazdaspeed 27.2 mm, 4 mm wall, fixed = 1.2
Hotchkis Miata 27 mm, hollow, three hole #22435F = 1.13, 1.34, 1.60
Whiteline 27 mm solid, 3 hole adj. (12.8 lbs) = 1.2, 1.5, 1.7
Eibach 27 mm solid adj. = about like Whiteline
Progress Tech Miata 1.125" (28.5 mm), 0.25" (6.35 mm) wall, 3 hole adjustable (9.1 lbs) #61.1132
AutoExe 28 mm, solid, two hole adj. = 2.22, 2.42
Cusco 28 mm, hollow
Tanabe, 30.4 mm, hollow, fixed = 1.7
Racing Beat 32 mm, 4.8 mm wall (9.4 lbs), fixed = 2.1
Progress #61.1152 / Agency Power 1.25" (31.75 mm), 0.25" (6.35 mm wall), 3 hole adj. = 2.1, 2.6, 3.1
Hotchkis 33 mm, hollow, three hole adj. #22437F = 2.10, 2.50, 2.95 (?)

 
Rear Bars:

Stock Sport “yellow dot” 16 mm, 2.6 mm wall (2.9 lbs) = 1
Mazdaspeed 17.3 mm, hollow, fixed.
Eibach Miata 16 mm hollow, adj. #5536.312
R3 “Orange Dot” 16 mm, solid F197-28-151 large side wing
AutoExe 17 mm solid, 2 hole adj. = 2.16, 2.47
Progress Technology Miata 11/16" (17.5 mm) solid, 2 hole adj. (5.2 lbs) #62.1132
Whiteline 18 mm solid, 2-hole adj.
Eibach 18 mm solid, adj? #5544.312
Cusco 18 mm, solid
Racing Beat 19 mm, 3.2 mm wall, fixed
Progress Tech #62.1152 / Agency Power 19 mm solid, 2 hole adj.
Tanabe 20.4 mm hollow, fixed
Hotchkis 21 mm hollow, three hole adj. #22437R = Hotchkis Miata #22435R

Great deal, did you pull the trigger on these yet?

Sure did, they arrived yesterday. Beautifully made, nicely powder-coated, and with very substantial bushings. Very reasonably priced too.

let us know how easily it installs, curious about this for autox (more so the front bar than the rear)

Any good ideas on the end links or are you planning on using the stocks? if so how do the stocks hold up.. and the 06+ miata sway bars work for the rx8??? didnt know that..

Interesting.

Install should be just like any other sway bar. Because of the beefy bushing mounts, on the MX-5 there's some small interference - they include a couple of doodads with the kit to fix that. No idea yet if that applies to the RX-8. It'll take me a month or so to get the install done. Garage gets cold when it 0 deg F at night.

I'll use the stock links at first. They are easily swapped when I get tempted to replace them. I like the PowerGrids because of their quieter bushing ends, but not sure that they can be adjusted for length while installed on the car. If not, AWR would be my second choice. Were I racing or anticipating on running the bars full hard, I'd probably upgrade now. D-Spec shocks with MazdaSpeed springs should be fine. Since the '06 Miata was based on the RX-8 chassis, their sways are a direct swap. A popular (and cheap) setup for Miata jockeys is the RX-8 "yellow dot" on the front, with a automatic-version RX-8 "red dot" for the rear. Brian @ Good-Win assured me these bars will work fine on the RX-8.

Sweet.

IMHO, most ppl "overbar" their cars. Perhaps that's my hangover from driving classic Detroit iron in my youth, but there's nothing much more miserable on the street than an undersprung RWD car with monster sway bars. Road racer Eric Meyer has stated that one should use the stiffest spring and softest bar to suit in dry conditions. (He has also said that goes to softer springs and little or no bar in the wet.) This may of course be quite different in autocross where the car spends much of its time "in-transition".

On TTAC there's an occasional series on suspension tuning where the expert claims that many confuse "sport" suspensions with quick turn-in and rough ride, when in fact, the optimal may feel less like this but result in faster track times. It has the ring of truth to me.

Again, very much my IMO, aftermarket makers assume the soft spring/hard bar combination and get ppl on board with that muscle car feel. Why bother with independent suspension when one's gonna weld the left and right sides together with a mega-sway bar?

But then, I'm not a racer ...

Beautiful list, I was actually about to post my own research on this since I am looking for something around the stiffness of the whiteline bar...

A few of the numbers you have posted are not accurate according to my research. The biggest one is the progress wall thickness. 6.35 mm is VERY thick so I emailed them and it seems like the wall thickness is actually half that (3.175mm) which makes more sense.

Also:

The front stock wall thickness is specced as 3.3mm
The front mazdaspeed outside diameter is 27.2mm
The hotchkiss numbers just look wrong. They are too low for raw rate of a 33mm bar, but look too high for wheel rate. The rear rates look about right for raw rates, but you can't get those rates at the wheel with a 21mm bar (so the opposite to the number for the front bar).

You can use the FCM spreadsheet to calculate stiffness. Put the outside and inside diameter into the table under "DATA FOR SPRINGS AND SWAY BARS".

Plug in the numbers and you get:

stock front bar: 1105.3 lb/in raw, 402.9 lb/in wheel rate
Whiteline 27 mm: 1746.5 raw, 636.7 wheel = 1.58x stiffer than stock

+1 on everything you said here. The popularity of stiffer aftermarket bars is due to it being an easy solution to market, and a relatively cheap and easy solution to install compared to changing out the complete suspension. The factory front bar on the RX8 is already quite stiff, so ideally one would be looking to go with a lower rate in combination with stiffer springs. The trade off is in daily driving ride quality. For that it is better to have a front spring wheel rate that is lower than the rear, which then means you need a fairly stiff front bar to get the balance right, and that explains why Mazda ended up with a fairly stiff front bar to start with.

Charles and Blu3dragon: Thanks for the additions/corrections. I'll do fixes when I get home tonight. It's proven very hard to get much real info on many of these bars. When one searches forums, some of the measurements shown don't agree with the specs and at the sub-millimeter level people round English to Metric conversions differently and also end up arguing about the thickness of the paint or powder-coating vs. the steel itself. Ads will disagree with each other and no one specifies the hole distances from the rotation axis of the bar.

I did however, find it useful to compile a list in order of presumed stiffness. For example, one can see that the Miata Hotchkis front is pretty reasonable for an RX-8, but their rear bar is outrageously stiff for the 8 and ridiculous for the Miata ==> oversteer central. Yet perhaps interesting to a drifter.

I've struggled with exactly the same thing and went down the same path... The sub-mm dimensions are more of a nice to have than a necessity. However, the uncertainty around the progress and hotchkiss numbers are far enough off to make a pretty significant difference.

It would be great if you can both weigh the Miata bar and measure the total arm length and the distance to each hole once you get it as that would allow both the side wall thickness and the leverage of the arms to be confirmed.

the Powergrid endlinks are nice, but I recommend these heavy duty M10 x 1.5 flange nuts rather their nuts

http://www.mcmaster.com/#cadinlnord/91005a037/=l715at

also recommend this same nut for the bolting the exhaust manifold onto the engine, the large flange with extra thread depth and 17mm hex head allows you to torque them nicely - be sure to use high temp nickel anti-seize on the manifold stud thread with them and you'll never have another manifold nut headache or ever need to replace them.

Charles, OIC. It's still good info. I'd gone to PT's website ( Progress Technology: Anti-roll bars, sport springs, coil-overs, camber kits and more since 1995! ) and searched for 06+ Miata sways. There weren't listed, and still aren't, nor does the PN you provided show up with a search on PT's site. However, a general www Google search with the PN and the word 'Miata' does indeed yield many vendor options. Odd that PT itself doesn't list them, but you are correct. I'll modify the original post to reflect this.

On the second item, I agree, but within some range of "reason". Yes, "reason" is also subjective, but most would probably agree say that a RX switch to leaf springs and a solid rear axle would be a bad thing. WRT sway bars, my opinion on them came with an IMO. One of the nice things about a forum like this is the ability to poll the experience of others to come up with a balance of opinions about this or that.

I do think though that BHR's next project should be a kit to swap the fog lights for photon torpedo launchers ... :rock:

Thanks for the tips. I'd been buying new Mazda nuts every time I'd taken the manifold off, but they are rather dinky.

Do you know if the Powergrids can be adjusted without removing and end? In other words, do they have a left/right threaded piece? I kinda think not, but it's hard to tell from the catalog pics.

I have them installed on my steam pipe size front swaybar and recommend them. They have the correct turnbuckle-style adjusters

Oh, it gets worse.

I measured the diameter of the front bar to be 1.133"
Good-Win claims it to be 28.5 mm = 1.12"
Considering paint thickness, roundoff error, and a USA-made product, the real diameter is likely 1 1/8" = 1.125" = 28.575 mm

If PT claims the inner bore is 1", then the thickness of 2 walls is 1/8" and one wall is 1/16" = 1.5875 mm. So thin, it's hard to believe.

So, will working out weights help? Both crude scales I have here give me a weight of 8.3 lbs for the front bar, but that could be off 1/2 lb.

What we really have here are a 1 1/8" diameter bar with either 1/16", 1/8", or 1/4" wall thickness. Take a density of steel = 7.7 gm/cc. From the estimated volume, the endpieces weigh .37 lb each (though I don't know how far into the tube they extend. The length of the tube is about 121 cm. From that I get weight estimates of:

(solid) => 13.88 lb
(1/4" wall) => 9.83 lb
(1/8" wall) => 5.93 lb
(1/16" wall) => 3.5 lb

So def not solid, or a 1/16" wall. Closer to 1/4" (6.35 mm) than 1/8" (3.175 mm), but I wouldn't bet on it.

3/16" (4.783 mm) ?

Aargh!

:crying:

Edit: Bought a better scale, 9.1 lbs +/- 0.15 ... so consistent with a 0.25" wall thickness.

Agency Power. Sway Bars - Agency Power

You need to quit playing on the internet and go work on your car instead

^ Excellent point!

Thankyou so much for taking the time to weigh the bar and for the very informative post. Motivated by this I ran the numbers through myself using a density of 7.9 and I get 4.8mm for wall thickness so agree with 3/16" (4.783 mm).

According to wiki the density of steel varies between 7.75 and 8.05 g/cm3, so using 7.9. For weight I used 8.3 lbs - (0.37 lbs * 2)

volume=weight/density= 434070.319 mm3
outside volume=pi*r2*lenght= 775975 mm3
inside volume=outside-volume=341904.6814
inside diameter=[sqrt(volume/pi/lenght)]*2=18.96770986
wall thickness=(outside diameter-inside diameter)/2=4.803645071

which is close enough to 4.783 for me to call it a win.

Using a density of 7.7 I get an inside diameter of ~4.96mm
With a starting weight of 8.3 lbs and a total lenght of 1230mm I get ~5.3mm. (This was my initial estimate ignoring the end piece weight you provided)

Also, the inside diameter progress gave me was for the RX8 bar. So, it could be that the RX8 bar uses a 1/8" wall, while the miata bar uses a 3/16" wall.

Following on from above, a 28.58mm bar with a 4.783 wall gives a raw rate of 1762.7, which is almost exactly the same as the 27mm whiteline bar and 1.58x stiffer than stock.

Assuming this is correct, then this is the bar I need :-)
At this point, that seems like a big assumption to make though!

I'll get a more accurate weight measurement later on. Rest of my weekend is full of movie events and cute actresses ...

thanks for starting a new thread on an old subject rather than just adding it on so all the misinformed n00bs can have a place to play

Now there's a topic more interesting. Picts or GTFO. :)

Oh you're so welcome. The old threads are scattered all over in both time and in different forums. One could hypothesize that getting by getting post 1 into reasonable shape to the point RIWWP could refer to it, it would cut down on the number of noob same-question threads.

Or not.

The weight with better scales is 9.1 +/- 0.15 lbs, which is more consistent with a .25" wall.

Your info emails on the PT RX-8 bar are inconsistent with previous info on that bar: 1 1/4" diameter, and 1/4 inch wall. One source: https://www.rx8club.com/wheels-tires...y-bars-109096/

another: Progress Technologies RX8 FRONT AntiSway Bar. for RX8 2004-2011

:dunno:

Hmm, thanks for the more precise weight. That's still a little bit lighter than what I would expect for a 0.25" wall, but I agree it is now close to that.

Actually knowing it is in the range of 3/16" to 1/4" is perhaps good enough. The 1/4" wall will only be ~12% stiffer than the 3/16" wall.

Well, thanks to the data from HiFlite I decided to order the PT miata front bar as combined with the adjustments it should be close enough for my needs. If there is any way to actaully measure the stiffness when it is on the car I'm all ears.

Thanks, I had some crazy ideas about jacking up one side of the car while on some scales, but I don't have easy access to any scales anyway. I think I'll just try driving it, see how I like the balance, and then adjust from there.

So this thread turned me on to the FCM calculator and I guess I have a couple of questions for the more experienced.

https://www.rx8club.com/attachment.p...1&d=1371669250

So above is a snippet of my results, and there are a few things that make me :scratchhe. So reading some of their resources on the value each of those columns has, I was focusing a bit on the bounce frequency.

They mention that higher bounce frequencies can induce worse traction on the road when hitting bumps and that ideally, for a non-dedicated race vehicle, you want the frequencies to be about 1.8. Now my question is, how exactly does damping come into play? For example, we can see that my bounce frequency on the front is "high", now can that not be compensated for by increasing damping on the coilover, and furthermore, is that what one would ideally do to balance my setup more?

Also, how would one simulate running no rear bar? Putting a 0 in the rear sway size throws some of the numbers out of whack, whereas putting a 1 in the sway diameter and thickness seems to make more sense.

Hmm, bounce frequency is a measure of how stiffly spring the car is. For a track or autocross car, you want to be up around 2.3-2.5Hz. That's not going to be too comfortable on the street. I think the 1.8 figure is basically seen as a good compromise between street comfort and performance. You also want the rear to be slightly higher frequency than the front (5-10%) so when you hit a bump, both ends of the car land at the same time (the faster rear catches up with the slower front). When setting the front to rear spring rate ratio though you also affect the balance of the car. So, if you change this, you need to change the sway bars to compensate.

Yes, if the damping is correct then it will help keep the tire in contact with the road.

On the sway bar settings, putting 0 in seems to work for me.

I've since started using the NC calculator. It is a little more flexible and you can edit all the fields to input the RX8 values.

https://www.rx8club.com/attachment.p...1&d=1373497185

That calculator looks great blu3dragon. Is it available to the public?

I did not see wheelbase in the calculator though, and I think this will affect the ratio bounce frequency. The wheelbase will also affect the pitch frequency, but that isn't listed on your spreadsheet.

Do you mind sharing the equation that provides the ratio bounce frequency?

Thanks for the info blu3. I will check out the NC calculator and report results.

JCrane: FRC_NC.xls

Ok so here is my results with the NC sheet and after realizing how to put in solid bar data. Setup 1 is what i run daily, and what i run at autocross. Setup 2 is what I would have if I threw on 8K in the rear. I have a set of 8K swift springs sitting in my garage which is why i put that data there, just for comparison.

The ratio bounce frequency is simply (rear bounce freq/front bounce freq). Wheelbase does not change that, but wheelbase and speed will change the way the car pitches over bumps. I have not done the math on the rx8, but ~10% higher rear frequency (so a bounce ratio frequency of 1.1) is a good ballpark to aim for, with any thing in the 5-15% (1.05 to 1.15 BRF) range acceptable. This is for ride, for racecar, then you are more concerned with front to rear roll couple (FRC) to get the balance right.

Thanks for sharing. How do you find the balance with your current setup?

What bump stops are you using - are the bump stop rates you used correct?

I'm going to try and dial my balance (FRC) in this weekend which will be the first time I drive on track with coilovers and sway bars.

I actually used to have 8K/6K on my stance coilovers, but then at the advice of another member who autocrosses their 8 a lot, i bumped up to 11K and left the 6K in the rear. It gave me an insane boost in confidence on the track and after about 4 clicks up from full soft and a disconnect of the rear bar, I started really putting down my best times (my definition of 'best times' is my delta from the first place finish in my class, they are generally the same group of guys).

I am not too sure what to put down for bump stop. I am using the ones that came with stance coilovers. I can't seem to find any data about their size or rate online.

2 questions:

1. based on what you were saying about about the bounce freq.... if i wanted more street comfort, I would be using the 11K/8K setup, and for a more aggresive track setup, I would stick with the 11K/6K?

2. Any idea what the front arm measurement would be on a swaybar on full soft?

edit: *derp* just noticed you had the full soft measurement above ;)

Hrmm, interestingly enough, it looks like I should keep my rear bar on and my front on the softest hole as it will put my FRC closer to 69%? I am reading through the FCM tutorial and it comments on how a AutoX Miata shoots for about 65%

And even lower if you go with the MX5 Bar in the front, while keeping the PT rear bar.

^So you are thinking 69% FRC since the RX8 has more power than the miata? I was actually aiming for 66% expecting that to give me slight understeer at the limit (the first row in my screenshot is my starting point this weekend...).

It is likely your bump stops are stiffer than 100 lbs/in since those are the softest ones FCM have. Stiffer bump stops will bring that FRC down. Given your experience and the unknown here, I would just use the spreadsheet as a guide to increase or lower FRC based on whether you want more front or rear grip.

In theory, you want to set the springs right first, and then tune FRC with the sway bars (and finally bump stops). So, I'd expect the stiffer 11k/8k setup to be better for racing/AX as long as the shocks can control those stiffer springs. If I were you I would try that, along with bars to keep the FRC where it works for you (11k/8k with the PT miata front bar and no rear bar should give you similar balance/FRC to your current setup) [EDIT: I meant miata front bar on softest setting. Stiffer bars reduce grip over mid corner bumps, so softer bars with stiffer springs is better for handling than softer springs with stiffer bars]

On your other question, I would expect the stiffer rear springs will have more effect on ride than the improved bounce frequency ratio. No way to know without trying it though :)

And yes, I measured (well more eyeballed) my front sway bar holes to be 15mm apart, with the furthest hole giving an arm length of ~200mm (leading me to trust Shaikh's 187mm measurement for the middle hole)

Well I only mentioned 69 because it was the lowest I could go, for "free" lol.

So here is what would happen with:

Front bar on full soft
Rear bar on full soft
11K front
8K rear
200mm bump stops (set arbitrarily, only affects the last column)

^Unless you have a lot of understeer right now, I would guess you are going to get too much oversteer going that far! However, front bar on medium, or hard, with rear bar on soft will probably work well.

Same as above with front bar on medium

This only gives me an imbedded spreadsheet in html format. Do you have an excel file?

Nope, I am just using it in a browser and then "saving" my work via a screenshot.
The spreadsheet is created and owned by Fatcat Motorsports.

OK, sounds good......I will update this thread with my current settings and my impressions as to how I like my current setup. I will also include alignment settings for those interested.

Swapped my rear swift springs to 8K. So far loving it on the twisty backroads near my house.