rear sway vs no rear sway FCM calculator - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-21-2011, 03:42 PM   #21
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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.
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Old 12-21-2011, 03:47 PM   #22
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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.
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Old 12-21-2011, 03:50 PM   #23
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Originally Posted by ChrisGriffin View Post
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.
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.
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Old 12-21-2011, 05:31 PM   #24
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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...
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Old 12-21-2011, 05:56 PM   #25
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Quote:
Originally Posted by Gryff View Post
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.
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Old 12-21-2011, 06:03 PM   #26
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Originally Posted by Gryff View Post
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...
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).
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Old 12-21-2011, 06:19 PM   #27
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949 has a formula, it works. There are varying opinion on it and personal preference, trial and error is unavoidable.
Formula please!
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Old 12-21-2011, 06:38 PM   #28
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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.
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Old 12-21-2011, 06:44 PM   #29
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Hustly, I has not enough monies for baller 949 suspension, otherwise I would. Im trying to make what I have work.


Quote:
Originally Posted by Track View Post
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).
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.
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Old 12-21-2011, 08:14 PM   #30
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Well, at least my 450/300 rates will be good with my weanie tires.
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Old 12-21-2011, 09:06 PM   #31
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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?
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Old 12-21-2011, 09:10 PM   #32
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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?
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Old 12-21-2011, 10:00 PM   #33
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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.
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Old 12-21-2011, 11:04 PM   #34
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Quote:
Originally Posted by Gryff View Post
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?
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.
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Old 12-21-2011, 11:25 PM   #35
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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...
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Old 12-22-2011, 12:35 AM   #36
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why remove for street?? whats the difference, dont drive like a bitch boy.
It make a huge difference getting power down on windy roads in the rain and snow and on gravel.
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Old 12-22-2011, 01:10 AM   #37
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@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.
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Old 12-22-2011, 01:23 AM   #38
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@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.
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Old 12-22-2011, 07:37 AM   #39
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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.
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Old 12-22-2011, 09:43 AM   #40
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It make a huge difference getting power down on windy roads in the rain and snow and on gravel.
eh.
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