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.

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.

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.

I like a car that turns, leave the sway.

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 :(

I liked mine removed on the street.

On the track/autox though I'd listen to these /\ guys and leave it in.

why remove for street?? whats the difference, dont drive like a bitch boy.

Turn in is better with a sway.

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.

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 :dunno:

id have to actually drive it myself again to tell the difference.

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.

Sounds/looks like I need to pick up a stock rear sway.

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.

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.

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.

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

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.

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.

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

Could someone explain what is trying to be determined by the FCM, I have done some suspension work but never seen this much thought put into roll rates at this level. I have seen this on multiple Miata forums.

The calculator let's you know generally how the car is going to behave on the track before you order the parts. If you already have 600/300 springs it can help you choose sway bars so your not just guessing in the dark.

FCM is FatCat Motorsports. He/They have developed a suspension calculator which will roughly indicate your Front Roll Couple based on the spring rates and sway bar of your choosing. A few things to mention, the Motion Ratios are measured and have changed slightly. Not sure how correct the NB ratios for both the sway bars and the control arms are, but its pretty close.

http://www.fatcatmotorsports.com/
go to FAQs, Tech Articles > Online suspension calculator.

Its more about the balance than roll rates, although its nice to "compare" your roll rates with spec miatas since we run different rates and sway bars.

This is the stuff that gets me so confused... I kinda wish we had a sticky that stated what every kind of change to the car would do. Although that would have to be huge. But its the kinda thing where, im trying to get less understeer out of my car, do I put a bigger front sway, lower tire pressure, more/less camber f/b ratio, up spring rates? I like what fcm does, but sometimes I cant make heads or tails of it...

949 has a formula, it works. There are varying opinion on it and personal preference, trial and error is unavoidable.

while you can use tire pressure to change balance you generally want to set it and camber down right based on:

Tire pressure - based on conditions and temp. for full tread use.
Camber - for even or graidented tire temps.

Not sure what the f/b ratio is

Unless your rates are totally whack (230 front, 200 rear?), you probably should not have to change that either. Spring rates are usually pre-determined based on a bunch of suspension geometry stuff and bounce frequency. We got it easy, because spring rates on the beat have been beaten to death.

Which leaves sway bars. Your sway bars should be the biggest balance factors and perhaps the amount of toe you run. For the most part, the plaguing understeer we had was mostly due to shitty alignment (I fixed mine btw, I got some new toys and figured out some mistakes we made).

This part may not always apply, but I have read/heard this on a few occasions from a couple of TT and racers: If you are not particularly towards the grip limit on the tires, the car may have a tendency to understeer since that's how our suspension is setup. What it means is, avoid going slow enough to accelerate (keep maintenance throttle) before the apex (although some corners you are supposed to do that. For example turn 7 at RA, you actually start to track out before the apex).

Formula please!

lol



Sorry! If you have a 90-97 Miata and do not have factory NB mounts and hardware, you can just add them to your Xida Club Sport order for a complete ready to bolt in system. If you have a 99-05 Miata or the upper shock mounts from same, just order the Xida Club Sports without mounts.

For race tired cars with track performance as the main goal, we generally start with 700/400 rates. If you all of your local tracks are really rough and bumpy, then drop to 600 or 650 from and 350/400 rear. If running 275 Hoosiers on smoother lots or 225/45's on 9" wheels with noticeable aero downforce, 800/500.

For a mostly daily driver that only sees occasional autocross or track use, 550/350 if using really sticky street tires. For medium or small (205/50 on 15x7) street tires on a mostly street car, 450/300 rates. If running an LSx conversion, sames rates apply. If running a small block Ford conversion, add 100# front and 50# to each recommendation range. If you are still not sure, give us a call. We'll get the system matched exactly to your needs.

Hustly, I has not enough monies for baller 949 suspension, otherwise I would. Im trying to make what I have work.


Whoo new toys! lol, I know that the alignment has a good bit to do with things, but I cant help but feel like there is more to it than just that. I suppose the only logical step is to fix the alignment and see where I stand after that is done.

Well, at least my 450/300 rates will be good with my weanie tires.

Gryff, if you post what youhave now I can fix your understeer problem. I need spring rates, alignment numbers, and what sways do you have?

kyb AGX with ground control springs, so 350F/275R Stock sways, 19mm front, 12mm rear (sways are stock to my knowledge)

Last known alignment numbers. (Iknow theyre bad, wasnt what I wanted, long story.)

Toe 1/16th in all corners, I zero'ed the toe in the front as best I could at the track. turn in was better.

3 deg front camber,
2.5 rear.
caster was somewhere around 3 deg?

Doesn't look like a setup that should understeer, in fact quite the opposite. Use zip ties on your shock shafts to see if the front is on the bump stops also lube the front sway. Your around 49% on the fatcat calulator.

I checked my toe when I got back, driver's side had about 3/8th toe IN lol.

I am at 3mm total toe out, which is 1/16th on each. we will talk more on g chat.

Whoops! I got my spring rates wrong, 375F/250R 55.9% FRC

I really like the zip tie idea, Ill give that a shot, see where that lands me. plus it cant hurt to lube the sway joints while im under there.

joe, hmmm, that may explain a bit...

It make a huge difference getting power down on windy roads in the rain and snow and on gravel.

@wayne, Having no rear sway on the street or autox is ok, the big track is another story.

@gryff, 55.9 is not bad. You have something funky going on with the diff, tires, alignment, sways, or bumpstops. Start investigating.

@jake: Thats what Ive been saying. I don know a good way to look into each aspect. The bumpstops make sense by using zip ties. tires shouldnt be an issue, they are not that old, and I rotated them halfway through the weekend, no change in handling. anything else to check with them?

What do I need to check with sways? lubed up right, not binding, ect?

same for diff...

As far as alignment, I told you what I had above. Im aiming for something like 2-2.5 front, 1.5 rear 0 toe front, 1/32 toe in rear. and 5 deg. caster next time I get the car aligned.

When do you get understeer Gryff? At turn in or track out? I ran the same setup as you, and if I even looked at the accelerator mid turn the car would have its tail out the rest of the way through.

What I have noticed is that ride heights can have a HUGE impact, no matter what springs you are running.

Zip ties are useless on a miata with GC coils. I can pretty much guarantee you that you're using the bumpstops at those rates.

eh.

I think Wayne means winding

When was the last time on track you were 'trying' to induce oversteer Collin? On the skid pad - before you ran over the railroad ties? :) sorry, couldn't resist!

I regularily disconnect the rear sway when the track is wet which helps keeping the rear in place. I'm running 500F/300R on GCs/Koni yellows and still sometimes have understeer issues, usually going into a hairpin too hot - have Emilio's track alignment setup. In for baller Xida setup...

it was on purpose, so he can get more front camber.:giggle:

@joe & Bryan: you guys are assholes...
just thought you would like to know.

bryan, I was trying to make it better, The turn in was a lot better on Sunday, but not great. but yeah, I knew I wasnt going to be able to completely fix it, this is an issue I have had for a long time. like since I have had the car kinda long time. I feel like I need to look for bent stuff tbh, but not sure where to start, or how to start.

Understeer is everywhere. turn in, mid turn, and track out. I would be full throttle through the entire turn with not even a hint of oversteer. Ride heights if I remember correctly were 4.75" from all of the pinch welds? I know it was very close to 949 reccomendation, if not right on the money, but my car does seem to sit lower than most. I'll go measure it again for the heck of it.

:rofl:

For not-so-serious cheap redneck testing - you could sammwich in some of those rubber coilspring blocks to 'stiffen' the rear springs, but would be at a loss for what 'compareable' rates would be - not to mention adding to rear ride height. Again, it's a cheap ass thought for trying something to see what it does - just avoid the sprinkler head, wich I'm so glad you did NOT hit! :giggle:

and bust your power steering while you are at it. he did some good donuts though, I am jealous of stupid amounts of power on all season tires...then again, not really!

Yeah me too! thats what I get for using a skidpad at night, and assuming that road atlanta was nice enough to have a auto popup sprinkler head... oh well, nothing broke or bent :loser:

Joe, that was his fault... all im saying

Might be worthwhile to have somebody drive your car. You may be driving at street tire limits on r-comps for example. A good clue is if you can't rotate the car under braking.

not sure I 100% understood what your saying, but im on street tires, not R-comps.

see above.

That is a possibility as well. It may be helpful to have someone else drive my car at cmp, see what their thoughts are as well.

Dean is talking about adding slip angle with trail braking.

If its understeer all over, then something is wrong. My guess is you have some kind of bad binding going on in the front suspension.

WAG, Id say the only thing causing your understeer is the toe in everywhere. I know you said you tried getting rid of the front toe in to zero, but you should never want front toe in. Toe out is the way to go and it doesnt just affect turn in, it affects the entire turn. Something to do with ackerman I believe. Toe in in the back is an aid to help putting power down in corners but it doesnt sound like thats your problem so get rid of it. Never dial in rear toe in on a pushy car, it makes no sense.

There are other aspects of your set-up that could be causing the push too. You have plenty of camber all around according to your numbers. Well, you may not need it. You say street tires but what kind of street tires? All season radials or sticky extreme summer tires? If the all season variety then I would expect the push and blame the tires and you have no choice but to slow down. If you have sticky summer tires then you have a handling issue or you just need to slow down. Tire pressure could also be causing it. I would say about 30f/28r is a decent starting place. Raise rear tire pressure to help with understeer unless the fronts are rolling over.

Front shocks bottoming out, sure. How much travel do you have at static ride height before hitting the bumpstops? Easy fix to get more travel is to run NB mounts.

Sway bars I dont think would be in bind unless you have urethane bushings for body mounts. The stock bushings are rubber and dont require lube and are generally loose and get looser with use.

And take this advice FWIW. Ive never been on a track, just an autoxer. And I am not some suspension set up genius but I have had to deal with getting a car to handle like I like it and know that small adjustments make big changes.

I had problems with my front RB bar binding and then hitting the control arms, explaining gross mid-corner understeer. Once I fixed that I found the sweet-spot dean speaks of where you can increase trail-braking rotation with pedal pressure...it's a sweet feeling when you hit it You'll suddenly have a single tear in your eye, the clouds will part, horns will call out, and a sparrow will carry the message for all of the world, your glorious chariot has a arrived, behold it's glory.

I have the complete opposite experience with toe.. as long as its a degree here or there the differences are small. It can exaggerate an already present condition, but not cause terminal understeer.

But I have had the same experience as hustler with fat front swaybars. The bushing fit is usually terrible and there can be a LOT of bind in there. Its shocking how poor the fit is of the US made kits out there.

Ride height variations are also a big influence. I found that half an inch of added ride height in the rear more or less cancelled out the influence of the fatty arb up front. Make sure to measure ride height on a 100% flat surface.

Good thread.

My two cents. The FCM worksheet allows for a quick assessment of comparative setups, and what-if checks based on what you already have and what you might consider getting to change the balance. But, as mentioned there are a lot of other variables beyond springs and sways that make a big difference: front to rear rake, tire pressure, alignment, and power output to name a few. Personally I have used the spreadsheet to get my setup close, and check things like spring rate combinations. For example, if I change the front rate, what do I need to do to the rear rate to keep the same balance? Then when I get to the track I make relatively small adjustments and the car ends up being balanced to my liking.

Chronic understeer sucks. Been there. Get rid of it and you will be a lot happier.

Are you talking about removing the rear bar and running stiffer springs to maintain FRC?

If you run without a rear sway but also run stiffer springs, so that the FRC is the same, I believe *transient* turn in at the end of trail braking (lifting off brake), should improve because the weight transfer from front to rear is quicker and the tires get "upset" a bit more, over a shorter period of time.

If you keep your total roll resistance the same and the FRC the same, but increase spring rates (and by necessity reduce swaybar rates), the roll natural frequency remains the same but the heave (bounce) frequency and pitch frequency increase.

Cool, Ill zero the toe and play with tire pressures a bit next time im driving.
for the record, tires were 32 psi all around, potenza re-11.

Happy New Year! @Damir, sorry I dont speak degrees in toe alignment. Im an inches kinda guy. Im a dinosaur I know, but this whole thing of degrees and minutes and seconds is too technical for me. He said he has a 1/16 of toe in each side so a total of 1/8" toe in on the rear. I would be willing to bet thats more than a degree or two and would make a noticeable difference. On the front it gets worse with a lowered car as you end up with the steering arms in an upwards arc already so toe in makes it even worse and not just in turn in but the whole turn. And you make a good point that rake affects the handling of a car and can be a helpful adjustment in balancing a car out. I forgot to mention that. Unfortunately for Gryff, I dont think he has control of his ride height from when I read his set up. If he does then definitely, jack the weight around.

And I think re11s are pretty sticky so keep tinkering with things one at a time. I know rear toe isnt easy to change and get right but front toe is. Tire pressure is easy. I dont think the FSB is binding as it is stock but if it is binding, remove it or disconnect it. However, getting rid of the front roll control it provides may not help the balance at all but at least you can try it. Good luck.

I can, I need to find a flat spot to measure things before I make any changes though.