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Old 12-20-2011, 02:20 PM   #1
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Default rear sway vs no rear sway FCM calculator

I've been reviewing the rear sway vs no rear sway, and it seems to be about 50/50 with what people choose to run.

Here is one thread https://www.miataturbo.net/showthrea...ate+calculator

Using the fcm calculator I was shooting for about a 61% F/R bias.
http://fatcatmotorsports.com/FRC_TUT...S_TUTORIAL.htm

Does the sway matter as long as you reach the desired bias?

i.e 400/250 with stock sway(61%) or 450/300 no rear sway(63%). The bias is basically the same (I don't think I would notice 2%, since it is an ideal estimate), but I like the idea of a little stiffer spring.

Last edited by miatauser884; 12-20-2011 at 07:28 PM.
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Old 12-20-2011, 03:30 PM   #2
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Don't remove the rear sway. Without it, the inside rear doesn't unload like it should, and the car won't turn in properly.
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Old 12-20-2011, 03:32 PM   #3
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I run teins with stock rates so 7/6K, with a 7/8" bar on the stiff setting, and the stock rear 12mm.

This brings me to like 51% FRC, or something. I love it; and that's coming from a calculated 60% (450/250). I don't want to change I thing. I'd have vairous other rates, ratios, and sway bar combos, and they all either pushed like a snow plow or were uncontrollable.

I agree with Sav, autoxing without the rear bar was impossible, I couldn't turn "nimbly". Any hairpins were a joke.

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Old 12-20-2011, 04:25 PM   #4
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I like a car that turns, leave the sway.
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Old 12-20-2011, 05:39 PM   #5
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For the street, I like no sway. I did a two day back to back autox one day without sway and one day with a rear sway. The car drove much, much better with the rear sway in.

I wish I hadn't lost mine :(
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Old 12-20-2011, 05:51 PM   #6
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I liked mine removed on the street.

On the track/autox though I'd listen to these /\ guys and leave it in.
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Old 12-20-2011, 06:49 PM   #7
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why remove for street?? whats the difference, dont drive like a bitch boy.
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Old 12-20-2011, 07:23 PM   #8
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Turn in is better with a sway.
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Old 12-20-2011, 07:30 PM   #9
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OK, what bias is everyone else running? Brains bias surprised me. I thought the FCM thing was the bees knees. What should I be shooting for as far as bias? The FCM calculator suggests my current setup is a touch over 51%. I thought this felt a little tail happy in high speed cornering at the track. The car didn't loosen neutrally, but the back end started to break loose. However this was on a tight off camber turn. I was able to throttle steer easily on longer sweeping turns.

So rear sway in it is, now which one: FM front bar, stock rear with 450/300 nets 59.3%. FM rear bar 53%. Based on Brains review, keeping the the FM sways and changing springs seems like the way to go.

Last edited by miatauser884; 12-20-2011 at 07:50 PM.
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Old 12-20-2011, 07:41 PM   #10
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that same bias in y8s car is pretty oversteery, but his rs2s are dead, they have no grip. maybe my car just has no power.

it's probably because of how my front bar is set. but then again he has an NB and a tubular front bar

id have to actually drive it myself again to tell the difference.
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Old 12-20-2011, 08:01 PM   #11
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Quote:
Originally Posted by djp0623 View Post
OK, what bias is everyone else running? Brains bias surprised me. I thought the FCM thing was the bees knees. What should I be shooting for as far as bias? The FCM calculator suggests my current setup is a touch over 51%. I thought this felt a little tail happy in high speed cornering at the track. The car didn't loosen neutrally, but the back end started to break loose. However this was on a tight off camber turn. I was able to throttle steer easily on longer sweeping turns.

So rear sway in it is, now which one: FM front bar, stock rear with 450/300 nets 59.3%. FM rear bar 53%. Based on Brains review, keeping the the FM sways and changing springs seems like the way to go.
I am probably not the best to give advice on this, but depending on your application (track or autocross), it will make a difference. Generally, you want to run slightly understeery so as you get on the power, you have some grip available to you in the rear. Think about it this way, if you are oversteery you are already using all your available grip, as soon as you get on the power, you will start to slide. But if you are understeery, you can use trailbraking at turn in to get the rotation you need and then at the apex you power out as per how much rotation you want and roll on the throttle (And maintenance throttle in the inbetween, as we don't all trailbrake to the apex. Also, you don't want pig awful understeer, just enough to give you the grip you need so you can be at "more than maintenance" throttle after the apex).

I don't really know if that makes sense, but that's the way I understand it.

As for a % number, if you look at xidas 800/500 add in the 1.125" RB hollow and either stock rear or 14mm mazdaspeed rear, you will find thats about 59-60% on the NB. I think thats pretty close to the setup that Emillio runs on the enduro cars (I don't really know what they ran), so thats a naturally aspirated car at ~150 hp.

if you are churbo'd you will need to put in other people's turbo setups in your general application and go from there.
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Old 12-20-2011, 09:36 PM   #12
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Sounds/looks like I need to pick up a stock rear sway.
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Old 12-21-2011, 02:35 PM   #13
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Quote:
Originally Posted by djp0623 View Post
So rear sway in it is, now which one: FM front bar, stock rear with 450/300 nets 59.3%. FM rear bar 53%.
I have those same spring rates and sway bars. The stock rear bar is on the car and the FM hangs on a hook in my garage. With the FM rear bar the rear has a slightly greater tendency to step out if you overcook a corner and I found myself tiptoeing through certain turns at VIR. With the stock rear bar the handling balance is more neutral, breakaway is much more predictable, and the car generally inspires more confidence IMO.
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Old 12-21-2011, 02:43 PM   #14
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Simple answer:

Set up suspension with stock rear bar in place.

Drive car.

Too much power-on oversteer? Disconnect bar.


Personally, I disconnected my rear bar after an... incident occurred on the street during which much tire smoke was generated and a small tree was uprooted by my rear bumper.
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Old 12-21-2011, 03:10 PM   #15
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I don't care about the FCM set-up, 949's info is the king of fast cars around here. I don't like auto-x, but I could not enjoy a car with a soft swaybar. I'm running 700/400 springs, RB front sway, FM rear sway on middle setting, and the 949 alignment.

The real answer is the set-up that allows you to get the car in and out of the corner clean, fast, and comfortably. John drives my car a lot and we both agree that it's predictable and easy to drive, but my car is a tough stiffer in the rear and it's all personal preference. Follow Joe's logic.
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Old 12-21-2011, 03:18 PM   #16
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In layman's terms, what does each hole in the FM ear bar represent. I just put it where Shaike said to, which made it the least intrusive (softer) iirc.

What does moving the bar from one position to another accomplish, and what is it doing to the geometry? I plan on running the stock sway since the softest setting on the FM seemed to cause oversteer in cornering. W
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Old 12-21-2011, 03:34 PM   #17
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I shoot for 57 on a lower hp Miata and 60 if you have a turbo. If you can't get the right bias with a rear bar them pull it until you can get a new set of springs. Changing the holes changes the spring rate of the car. I making this up as an example but let's say the three holes in a rear sway are 600, 650, and 700lbs. The stiffer you run the car the looser it will get. Sway bars are a tuning aid.
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Old 12-21-2011, 03:35 PM   #18
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Quote:
Originally Posted by djp0623 View Post
In layman's terms, what does each hole in the FM ear bar represent. I just put it where Shaike said to, which made it the least intrusive (softer) iirc.

What does moving the bar from one position to another accomplish, and what is it doing to the geometry? I plan on running the stock sway since the softest setting on the FM seemed to cause oversteer in cornering. W
Total bullshit ahead:
changing the attachment point, changes the arm length. by changing the arm length you are effectively changing the leverage point where the force is applied on the sway bar. the shorter the arm, the stiffer the bar.

Use your sway bar to fine tune balance. Ideally you would have an "infinitely" adjustable sway bar, but thats not really possible, so you make do with 2-3 settings. This is also not just 3 settings, as one side on stiff and one side on lesser will average out and is completely kosher to run (from my readings at least). Not sure about the mazdaspeed bar, I would assume that its one setting, but I seem to have enough adjustability in my front bar for all the balancing I need. That may change as I get faster though, I still have to take this setup out to CMP which is probably my strongest track at this point.
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Old 12-21-2011, 03:39 PM   #19
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Quote:
Originally Posted by Track View Post
Total bullshit ahead:
changing the attachment point, changes the arm length. by changing the arm length you are effectively changing the leverage point where the force is applied on the sway bar. the shorter the arm, the stiffer the bar.
It's not bullshit, that's exactly how it works.

Moving the attachment point further away from the fulcrum point increases the effective length of the arm, which has the same effect as softening the bar.
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Old 12-21-2011, 03:41 PM   #20
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Quote:
Originally Posted by Joe Perez View Post
It's not bullshit, that's exactly how it works.

Moving the attachment point further away from the fulcrum point increases the effective length of the arm, which has the same effect as softening the bar.
Thanks, I am electrical, so terminology falls short in my knowledge and would rather not get called out on it. lol
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