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Old 05-13-2013, 07:57 PM   #1
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Default Bar size for big spring rates?

Looks like I just scored a super deal on some Penske double adjustables for my SCCA track only miata. Already valved at 800 / 450, exactly what I was planning.

You guys with similar spring rates, what do you run for bars? What do you have, what would you change? I've used a 1-1/4" hollow (1/4" wall) speedway style bar in the past (f'n huge) with customer cars & they seemed to like it.

I know rear bar is mainly preference, so I can figure that out - But if someone has played with bar sizes & has a better idea I'm all ears
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Old 05-13-2013, 08:52 PM   #2
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RB .125" hollow FSB, MSM RSB.
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Old 05-14-2013, 07:42 PM   #3
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Emilio's got them wrapped in a bow, just for you: SuperMiata Sway Bar Kit Miata
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Old 05-15-2013, 12:16 AM   #4
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The ISC Speedway style bars are hugely adjustable with am length in the front variabl between 9.5 and 11” in the front and 4.75” and 7” in the rear. Stock arm lenths are 8.5” in the front and 4.8” in the rear. I calculated stifnesses and put them in order on Shakes Fat Cat suspension spread sheet.
One big advantage is they pivot on real very low friction pillow ball and rod end bearings adding nearly zero friction compared to big diameter urethane that can produce significant friction. One disadvantage is they are heavy like 4 to 6 lbs heavier than the hollow racing beats.

I’m currently running the front one off full stiff ISC3 and the rear full soft ISC1 with 800/500 lb springs.

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Old 05-15-2013, 12:34 AM   #5
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I hope this isn't too noobish a post, but for instance with RB rates you've come up with, which adjustment hole is that using?
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Old 05-15-2013, 12:59 AM   #6
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Quote:
Originally Posted by z31maniac View Post
I hope this isn't too noobish a post, but for instance with RB rates you've come up with, which adjustment hole is that using?
I think it is the soft adjustment hole. But I’m not sure on that for the front. The version of Shake's spreadsheet I have assumes everything has OEM arm lengths. You can adjust arm lengths in it but I don't have the data. The rear racing beat rear bar I have a sample of the soft hole is the same arm Lenght as stock. Stiff setting must be god awful stiff. I never used it when I was using the racing beat rear bar.

Actually I disconnected the rear bar when I autocross sometimes.

Bob
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Old 05-15-2013, 01:04 AM   #7
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I was curious because I'm researching setups for my DD NC, and for instance, good-win has most the bars effective rate for each setting. The Hotchkis bars are insanely stiff.

I'm pretty set on the big grip kit for the track rat when it comes time to change.
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Old 05-15-2013, 02:54 AM   #8
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FWIW For me I don’t think going any softer in bump or overall roll stiffness would be an improvement. On 275/35/15 A6's or on my Nitto track tires I witness full suspension bump travel usage frequently by the wear marks on my inner fenders both front and rear that require fully smashed bump stops to produce. For suspension to work It’s got to be stiff enough to not excessively blow through all the travel or rely primarily on the stiffness your bump stops provide as appose to your springs.

Also my car is a bit heavy street/track car but I run in the 1:32's at Pacific raceway on Nittos. ~9.5 seconds under the Spec miata Lap record. I have also raced it in a spec miata with not the best prep and made it just into the 1:42's.

Last edited by bbundy; 05-15-2013 at 03:07 AM.
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Old 05-17-2013, 05:14 PM   #9
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I am running 850f and 500r with SM 1.8 bars. The rear is set on full soft. Everyone tells me that is too much rear bar but I like they way it handles so I am reluctant to change it.

With the above setup the car is pretty tail happy till you are rolling on the go pedal. Once on power it feels great.

Driver style and preference varies so keep that in mind when playing with setup.
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Old 05-17-2013, 06:02 PM   #10
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thanks for the thoughts - I've had great luck with the big ISC front bar. I find it better to have too much front bar & adjust it soft than to run out of bar

So, with 800/450 springs & a big bar - think I can run an open diff? Trying to play the weight game (and avoid spending another $1k on setup).

KJ
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Old 05-17-2013, 06:07 PM   #11
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Quote:
Originally Posted by bbundy View Post
The ISC Speedway style bars are hugely adjustable with am length in the front variabl between 9.5 and 11 in the front and 4.75 and 7 in the rear. Stock arm lenths are 8.5 in the front and 4.8 in the rear. I calculated stifnesses and put them in order on Shakes Fat Cat suspension spread sheet.
One big advantage is they pivot on real very low friction pillow ball and rod end bearings adding nearly zero friction compared to big diameter urethane that can produce significant friction. One disadvantage is they are heavy like 4 to 6 lbs heavier than the hollow racing beats.

Im currently running the front one off full stiff ISC3 and the rear full soft ISC1 with 800/500 lb springs.

[IMG]https://www.miataturbo.net/attachments/race-prep-75/76684d1368588058-bar-size-big-spring-rates-sways-png[IMG]
Bob, I'm trying to understand the chart for other reasons than OP.

The rear bars are clearly labeled. But not the fronts. From what I gather the OEM NB front is 19 and rear 11 and the OEM MSM front is 24 and rear is 14. Is this correct?

Reason I ask is because I have the opportunity to swap in some OEM MSM sways onto my daily driven NB for free. Worth the hassle?

Sorry for off topic OP, but this is kinda sorta relevant in some weird way lol
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Old 05-18-2013, 02:12 PM   #12
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Quote:
Originally Posted by mrjones2 View Post
thanks for the thoughts - I've had great luck with the big ISC front bar. I find it better to have too much front bar & adjust it soft than to run out of bar

So, with 800/450 springs & a big bar - think I can run an open diff? Trying to play the weight game (and avoid spending another $1k on setup).

KJ
Unless you have some compelling reason to run an open diff, setting up the balance of the car tight just to save a the cost of a torsen will be less effective than running a torsen. If the budget allows, the OS Giken diff will be faster still.

We have played with FRC or roll couple bias, with stock NA bars (~300 in/lb) all the way through the highest rate RB bar (~1500 in/lb) and find as roll bars get softer, the FRC needs to shift towards the front (higher value). So less front bar means less overall rear roll stiffness to maintain balance. More front bar means more rear roll stiffness (lower FRC)

We like the 1100 in/lb Racing Beat 54107 bar for the 90-05 Miatas and the 14mm Mazda rear with springs in the 800/500 range for R compounds. 700/400 for UHP's like Rival, RS3.

Rear bar size is critical. Even 1.5mm bigger has a huge effect on balance. In arriving at the 14mm we now use, we have tried every step including some prototype bars in-between sizes. We found that for track and street use, the 14 allows fine tuning adjustments with small rear ride height changes and switching between the front two adjustments on the RB 54107. Over a wide range of tires, weight distributions, surfaces, weather we find the combo to work and have zero complaints from the many customers running them.

We see a lot of cars running the rear Spec Miata (Eibach) 15.875mm bar and reporting that the handling is always "a little loose but OK". Those drivers invariably do a bunch of band aid fixes to tame the looseness and think everything is OK. Set the car up just a wee bit more neutral with a slightly smaller rear bar and it simply turns harder. In w2w racing where a RWD car that is slightly loose at the start of 35 minute sprint race will inevitably have it's rear tires go off towards the end of a race (or 20 minute HPDE session) and lose time/track position. The unseen and frequently overlooked value of a more neutral car is consistency. For qualfying or TT (one lap wonder), we make small air pressure tweaks to free the car up a bit and all is good.

Bob likes a tighter car than we do so his choices will lean towards a car that plants the tail under power whether it's on entry, mid or coming off (he has driven and raced a few of our cars). Many years driving a 350whp Miata on old R compounds will do that to a guy . We like a car that will throttle steer on entry and mid corner and only plants at corner exit under full power.
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Old 05-19-2013, 08:16 PM   #13
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Quote:
Originally Posted by emilio700 View Post
Bob likes a tighter car than we do so his choices will lean towards a car that plants the tail under power whether it's on entry, mid or coming off (he has driven and raced a few of our cars). Many years driving a 350whp Miata on old R compounds will do that to a guy . We like a car that will throttle steer on entry and mid corner and only plants at corner exit under full power.
I need try try the 14mm rear and see what I am missing.

With the power differences of Crusher and Bob's car you would still set em up the same? I was thinking the reason Bob and I like the larger bar was due to greater weight transfer (harder acceleration) compared to crusher. It will be interesting to see if your thoughts change when your turbo kit is on.
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Old 05-20-2013, 03:59 AM   #14
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Quote:
Originally Posted by 18psi View Post
The rear bars are clearly labeled. But not the fronts. From what I gather the OEM NB front is 19 and rear 11 and the OEM MSM front is 24 and rear is 14. Is this correct?
OEM NBs used 11mm rears on the standard suspension and 12mm with the "HARD S" Bilsteins.

I run a 1" FM front bar (soon to be replaced with a 1.25" RB bar) and no rear bar, but then my car is primarily used for autox.

--Ian
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Old 05-20-2013, 01:49 PM   #15
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Yes as Emillio said I seem to like a bit tighter car than 949 setups. And I think it probably comes from my personal driving development coming in from the High horsepower Miata perspective. Or maybe I’m just a wuss and afraid of a car that might bite me.

FWIW I did some testing this weekend for Autocross at a test and tune which means I took the roll bar out the door bars and all the chassis bracing which is not legal in SSM. The cars chassis is lighter but noticeably flexier like this. Door bars which are not legal in SSM make a huge difference as would a cage. Running on 275 A6 Hoosiers so lots of freekin grip with stiff springs and the flaxiest Miata chassis there is. In this configuration and for this application I think the setup needs no rear bar for my taste. The rear bar seems to stop the rear helper springs from keeping the rear inside tire in good contact with the ground mid corner just as you want to start rolling back into the throttle. It’s kind of weird that in track mode the car feels like a pushy pig when I take the rear bar off but it doesn’t feel pushy in autocross mode. I’m theorizing high amounts of weight transfer to the outside front tire is enough to get the flexi un braced chassis to start playing a role in the suspension behavior and it gets more lift on the inside rear than you want. Tops CSP autocross cars never run rear bars I think I might understand why.

Bob
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Old 05-20-2013, 03:21 PM   #16
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Quote:
Originally Posted by k24madness View Post
I need try try the 14mm rear and see what I am missing.

With the power differences of Crusher and Bob's car you would still set em up the same? I was thinking the reason Bob and I like the larger bar was due to greater weight transfer (harder acceleration) compared to crusher. It will be interesting to see if your thoughts change when your turbo kit is on.
Same tuning. BTDT. Only real change is a bit more rear toe and a bit less rear camber when adding power. Don't ask me how much because it varies greatly with each situation. If it's a tad loose coming off with big power, look at temps, add rear toe and/or reduce camber as needed.


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Its kind of weird that in track mode the car feels like a pushy pig when I take the rear bar off but it doesnt feel pushy in autocross mode.
It's not the chassis, it's the dynamic situation. It's a common misconception that autocrossers need to be setup looser than road racers. The opposite is true. A road racer will never be asked to have the yaw rate and transition at full throttle in 2nd gear like an autocrosser will. The only time it's needed is on the out lap while I'm warming tires. So the autocrosser is defined by being able to put the power down while transitioning at 1g+ in 2nd gear. Being free in a long 4th gear sweeper is not something an autocrosser needs to be able to do.

In general, I suggest to my customers that do both to get the car dialed for track use then disconnect the rear bar for autocross. The exception to that rule is in ultra high grip autocross situations like a cool sunny day on clean concrete where a car running A6's might tighten up and need the rear bar.

Regarding the driving style thing, yes it's your style that's developed around big power. We low power guys are accustomed to going to WOT just after turning in. So we set the car up to maintain just the right slip angle with the snarling 125lbs of torque we generate. Lift and it tucks the nose in while scrubbing speed (noooo!). Big power guys just barely touch the throttle to set the rear then roll on as they track out.

I remember you driving our Rental a few years ago and commenting how it was too free mid corner, "wouldn't put the power down". The trick is to not lift in the first place
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Old 05-20-2013, 03:46 PM   #17
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Originally Posted by emilio700 View Post
Same tuning. BTDT. Only real change is a bit more rear toe and a bit less rear camber when adding power. Don't ask me how much because it varies greatly with each situation. If it's a tad loose coming off with big power, look at temps, add rear toe and/or reduce camber as needed.



It's not the chassis, it's the dynamic situation. It's a common misconception that autocrossers need to be setup looser than road racers. The opposite is true. A road racer will never be asked to have the yaw rate and transition at full throttle in 2nd gear like an autocrosser will. The only time it's needed is on the out lap while I'm warming tires. So the autocrosser is defined by being able to put the power down while transitioning at 1g+ in 2nd gear. Being free in a long 4th gear sweeper is not something an autocrosser needs to be able to do.

In general, I suggest to my customers that do both to get the car dialed for track use then disconnect the rear bar for autocross. The exception to that rule is in ultra high grip autocross situations like a cool sunny day on clean concrete where a car running A6's might tighten up and need the rear bar.

Regarding the driving style thing, yes it's your style that's developed around big power. We low power guys are accustomed to going to WOT just after turning in. So we set the car up to maintain just the right slip angle with the snarling 125lbs of torque we generate. Lift and it tucks the nose in while scrubbing speed (noooo!). Big power guys just barely touch the throttle to set the rear then roll on as they track out.

I remember you driving our Rental a few years ago and commenting how it was too free mid corner, "wouldn't put the power down". The trick is to not lift in the first place
A sweeper in an autocross course is about like the tightest hairpin in a road course. I can't think of a road course that I use second gear for with the 6 speed 3:63 and autocross is usually all second gear.
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Old 05-20-2013, 06:39 PM   #18
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Originally Posted by bbundy View Post
The ISC Speedway style bars are hugely adjustable with am length in the front variabl between 9.5 and 11” in the front and 4.75” and 7” in the rear. Stock arm lenths are 8.5” in the front and 4.8” in the rear. I calculated stifnesses and put them in order on Shakes Fat Cat suspension spread sheet.
One big advantage is they pivot on real very low friction pillow ball and rod end bearings adding nearly zero friction compared to big diameter urethane that can produce significant friction. One disadvantage is they are heavy like 4 to 6 lbs heavier than the hollow racing beats.

I’m currently running the front one off full stiff ISC3 and the rear full soft ISC1 with 800/500 lb springs.

I think the stock rear NA is incorrect on this chart. As I understand it, the stock NA 1.6 rear bar is 12mm and the 1.8 rear bar was 11mm.

I just ordered a 12mm rear bar to try on my NA with VLSD.

Last edited by wannafbody; 05-20-2013 at 11:49 PM.
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Old 05-20-2013, 07:38 PM   #19
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To illustrate the arm length difference between the ISC version of the speedway bars and racing beat or the stock lengths.

Attached Thumbnails
Bar size for big spring rates?-p1010004.jpg  

Last edited by bbundy; 05-20-2013 at 08:05 PM.
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Old 05-20-2013, 07:59 PM   #20
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To illustrate the arm length difference between the ISC version of the speedway bars and racing beat or the stock lengths.
The rearmost holes on the ISC bar look like they are too far rearward to reach the control arm tabs for the end links. What's the angle of the endlinks when they're in the rear holes on the ISC?

Is that a #54104 bar from a 90-93 which is shorter than the bars for the 1.8?
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