Talk Me Off the Ledge - Miata Spring Rates

I have read forums and otherwise researched this topic to the point of analysis paralysis and need some expert guidance. When it comes to Internet advice, I work with the assumption that 80% of what I read is baloney, but it is impossible to know which 80%. Hopefully, my fellow GRM folks have more actual knowledge and less Internet bravado on tap. Anyway, I'll try to keep it short.

I am an HPDE instructor, who just bought a mint 2003 Miata LS (no ABS) with low miles, and I want to set it up for 12 to 18 HPDE events per year plus driving to and from the track, some weekend cruising, and the occasional Friday commute to work in nice weather. It will not be used for any actual competition. Basically, I want the mythical Skittles pooping unicorn: as fast as possible on the track, while compliant enough on the street to be reasonably enjoyable. My budget for a set of coilovers is up to $2500, but less is better.

From what I can tell, there are two camps, when it comes to spring rates: stiffer is better (Xida (800), Feal (700), GWR (750), etc.) vs. just enough spring to do the job (FM (550), FCM (425), Ohlins (450), etc.).

The two main setups I have in mind at the moment are Xida and FM Fox. The suggested front spring for Xidas for a heavy NB2 is 800, which seems brutal, but reviews on this setup are positive--almost to the point of absurdity. FM Fox front spring is 550, which seems more reasonable in a vacuum. There are few solid reviews of FM Fox available that I can find. I can make either setup work according to the calculators I have used. Both companies appear to have valved their shocks appropriately for their goals, according to the dynos I have seen--with Xida being geared more toward hardcore track use, and FM Fox being geared more toward compromise between track and street.

Inputs into the decision include 15x9 rims with 225 tires with fairly aggressive alignment settings. The tires I tend to favor are in the 100 to 200TW range (Rival S, RE71R, NT01, R888, RC1, etc.). I doubt I will do much with downforce, if anything. This car will never see Hoosiers or the like.

Once all the noise is filtered, the argument seems to come down to controlling body roll with spring rates vs. sway bars vs. both. I have no idea which is better.

Can someone explain and support why I would want one setup over the other for my purposes or point me toward some literature that would help me make this decision? I get one shot at this, considering the cost involved, and I have to get it right the first time.

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Considering that you want the car to be streetable, go with the FM coilovers, because 800lb springs on a street-driven Miata is nuts. I'm sure it's great on a glassy-smooth track, especially if you've got a good bit of downforce, but those will be horrible on any imperfect street. Furthermore, the Miata has good suspension geometry so there isn't as much to be gained through spring stiffness.

I had the XIDA BGK 800/500 on my '90 Miata and ran 205 R88s on 15x8, -3.2/-2.5 camber f/r, 0 toe all around.

Car was fantastic, and I occasionally drove it to work and it wasn't uncomfortable at all.

I've also driven my buddies WRL Miata on Fat Cat's with 650/375....I didn't like the softer setup. It felt like the car took to long to take a set in the corner, it took me until the afternoon of the 2nd day to get "kind of" comfortable on the softer rates.

GameboyRMH wrote: Considering that you want the car to be streetable, go with the FM coilovers, because 800lb springs on a street-driven Miata is nuts. I'm sure it's great on a glassy-smooth track, especially if you've got a good bit of downforce, but those will be horrible on any imperfect street. Furthermore, the Miata has good suspension geometry so there isn't as much to be gained through spring stiffness.

Please don't impart your opinion on what spring rates are appropriate when you've never driven on said setup.

My local track Hallett, is very rough/bumpy, Keith can attest to that. 800/500 was perfectly fine. And I smash curbs so God doesn't kill kittens.

Significant aero and Hoosiers and guys are running 1000/500.

I have a car of similar weight and similar motion ratios on 650lb springs all-around, and I've driven a stock NB Miata, so I'm not just guessing or looking at the setup "on paper."

That said I assumed the springs were 800lb all-around since only one spring rate was specified, 500lb rear springs are reasonable but 800lbs front still seems very questionable to me.

GameboyRMH wrote: I have a car of similar weight and similar motion ratios on 650lb springs all-around, and I've driven a stock NB Miata, so I'm not just guessing or looking at the setup "on paper." That said I assumed the springs were 800lb all-around since only one spring rate was specified, 500lb rear springs are reasonable but 800lbs front still seems very questionable to me.

Ride quality with stiff springs is very, very, very dependent on the shocks. Good shocks that are valved well can lead to a nice ride with some shockingly stiff springs. Poor shock valving or crappy shocks can lead to even not so stiff springs having a back-breaking ride.

I've driven some of those revered high spring rate setups and let's just say that the reality doesn't quite match the online statements. One of the "I run 800 lb springs on my FCM setup and it's like butter!" guys threw me his keys and admitted to a bunch of weak points in his car's setup when I drove it. You can tell they're running a lot of rate. The really aggressive nose on the compression curve of the Xidas always makes itself felt, too - the front end moves around a lot with the road. It's a good setup if you have really fast hands on turn-in, it loads up that outer front immediately. Still, you can get performance without that compromise. I know we can be more aggressive on curbs with the Fox than some of the other guys because we don't limit shaft travel and we let the suspension move.

BTW, I run 750/500 with the Fox on my track Miata. It's surprisingly good on the street. Not something I'd choose for a daily driver, but you'll come home with your neck still attached to your spine. So if you want full travel and crazy spring rate, the Foxes can manage that. The 550/375 setup is the default standard rate, the sort of thing we use on fast street cars. My daily driver is in that range and it's the same front spring I ran in the Targa Newfoundland.

Historical viewpoint: the ultra-high spring rates you see now are a new development. 5-8 years ago, nobody would have considered it. Heck, for years we took flak for having springs that were just over 300 lbs for our street springs. Now they're called soft. It's a fashion. It's become uncool to let the car "breathe" over the road, it's got to be stapled down. It's true that shock damping quality is a factor, it's also true that 15 years ago there was no interest in $2000 Miata suspensions so nobody was working on them.

If you want an unbiased review of the Fox, wait until the Road and Track article about "19 Miatas in one day" comes out. I know the writer was really impressed with the Fox setups, and he was driving multiple setups on Laguna Seca back to back. I can probably put you in touch with Sam if you want to get his direct opinion.

There are also reviews of the Fox on other platforms, such as the NC and ND. I don't know why the NA/NB guys aren't posting reviews. It could be because of the near-religious enthusiasm that surrounds some of the favored products, it's tough to admit you bought something else!

Steve, if you want to talk give me a call. I'll be out of the office for the holidays and some work trips starting tomorrow, so today would be good.

z31maniac wrote: I had the XIDA BGK 800/500 on my '90 Miata and ran 205 R88s on 15x8, -3.2/-2.5 camber f/r, 0 toe all around. Car was fantastic, and I occasionally drove it to work and it wasn't uncomfortable at all. I've also driven my buddies WRL Miata on Fat Cat's with 650/375....I didn't like the softer setup. It felt like the car took to long to take a set in the corner, it took me until the afternoon of the 2nd day to get "kind of" comfortable on the softer rates.

What bars were on those cars?

I had a 600/375 (ish) setup on my NA with 15x9/225 Hankooks, no rear bar, RB 1.125" front bar. I know many go higher with front rates, and 600 definitely didn't seem too high/rough. I could see going higher on a smooth track. What I am curious about is if those running 800 or 1000lb front springs are still running the large front bar or not.

Edit: mine was STR prepped. I believe the common setup for STS/STR is the same as what I had except 700lb in front. It seemed a few years ago that that had almost become a 'spec' setup. Also, I wouldn't call the setup "comfortable" or "smooth" on the street. On flat pavement its fine, and you can drive it to the track just fine, but any transition, expansion joint, etc. was a bumpy ride.

GameboyRMH wrote: I have a car of similar weight and similar motion ratios on 650lb springs all-around, and I've driven a stock NB Miata, so I'm not just guessing or looking at the setup "on paper." That said I assumed the springs were 800lb all-around since only one spring rate was specified, 500lb rear springs are reasonable but 800lbs front still seems very questionable to me.

Trying to compare spring rates between two different vehicles, not on the same tires, or same dampers..........it's not even possible to make a comparison. Oh the lulz.

In reply to Keith Tanner:

FCMs are weak sauce. XIDAs are not. Also, I have absolutely no doubt the Fox are awesome. I was looking at buying your setup until my NC decided it needed about $3500 worth of work in the course of a week, so I ditched it. If I end up with an ND.......I'll be spending more money with you guys :)

In reply to ProDarwin:

I was running the 0.188" 90-97 bar on my car with the MSM rear bar. Running no rear bar seems like a recipe for terminal understeer. But setting up for Auto-X is different from the track.

I just replaced the stock Bilsteins on my MSM (the heaviest of the NBs). I went with Xidas using 700/400 springs and a RB 1.125" front bar (and kept the MSM rear bar). It's surprisingly comfortable on the street with the shocks set to 8 from full soft (out of 20 steps). The maximum rear ride height was a little low for me, but a pair of 3/8" spacers fixed that. No autocrosses yet, but I'm really looking forward to the first event next year.

Maybe I'm just used to the stock MSM suspension and stiff TR6 setups, but I'm fine with this for my daily driver. I certainly won't steer you away from the FM Fox setup because I have no experience with it. But the Xidas are amazing so far.

z31maniac wrote: FCMs are weak sauce. XIDAs are not.

I've never driven an FCM setup that really worked as advertised. The Xidas I've tried are better, but they still come across as race shocks on the street to me. The lack of overall travel (as noted by Joe) is an indicator of that, as is that fidgeting nose. There's no question that it's a better setup than the jiggly stock MSM suspension at least

The defining trait of the Foxes - to me - is a stability mid-corner that I haven't found anywhere else. I'm not sure I can point to where it is in the dyno charts, but man is it reassuring. The car is really stable and encourages you to push harder. Interestingly, it's also the only suspension that's really made the NA and NB platforms feel dated relative to the NC and ND. It's the first one that's fully taken advantage of the capabilities of the newer chassis and made them feel like more than just a different looking Miata. I haven't driven a Xida setup on anything newer than an NB, however.

^No doubt. But if the focus is mainly to be a track car, I'd go for more track oriented spring rates and valving.

Mainly a street car, it would likely be FOX all the way, but I haven't driven a Miata on those yet. But given how well the VMaxx worked, especially at the price point, I have no doubt the FOX setup is the balls.

z31maniac wrote: Running no rear bar seems like a recipe for terminal understeer. But setting up for Auto-X is different from the track.

We had a lot of trouble with a rear bar on the autox course. Seems to be the way most STS cars are setup: http://forum.miata.net/vb/showthread.php?p=7866834

I could definitely see putting it back on for track as you don't have slaloms or such abrupt changes in direction. Also probably don't have as many issues with wheelspin on corner exit (Keith and other people with 543254 horsepower excluded).

ProDarwin wrote:

z31maniac wrote: Running no rear bar seems like a recipe for terminal understeer. But setting up for Auto-X is different from the track.

We had a lot of trouble with a rear bar on the autox course. Seems to be the way most STS cars are setup: http://forum.miata.net/vb/showthread.php?p=7866834 I could definitely see putting it back on for track as you don't have slaloms or such abrupt changes in direction. Also probably don't have as many issues with wheelspin on corner exit (Keith and other people with 543254 horsepower excluded).

I could get my NB to spin at will with the rear sway attached. Even with it unattached it was easy to get oversteer if I wanted it.

I don't have my handy-dandy Miata suspension calculator available right now. What range of suspension natural frequencies are we talking about at these spring rates? If it's what I'm expecting, for the stated use I'd probably stick with one of the 'softer' setups. While the appropriately damped stiffer setups may be 'surprisingly not-uncomfortable' on the street, for me personally, the equivalently damped softer setup would generally make the car more enjoyable to drive more of the time...Making it more likely to get used more often.

When you're autoxing, you're in relatively low gears at relatively slow speeds in relatively tight corners. So you can rotate on the throttle when necessary, and the ability to put down power is really important. Autoxers seem to set up with a little more understeer to get that drive off the corner, pitching the car in to get it to rotate.

You have to take alignment into account as well. There are two basic setups out there, one based on an evolution of Mazda's original specs (a bit more rear camber than front) and one that's more recent (more front camber). Running the original will require more rear roll stiffness for the same balance.

The FOX can run big spring rates. I think they're good for 900+ in the front. That's just not the default spring set because it doesn't match what our customers ask for. Even then, on a pure track car, you want some compliance.

Keith Tanner wrote: There's no question that it's a better setup than the jiggly stock MSM suspension at least

For ride comfort, I've come to prefer the stiffened TR6 suspension over the stock MSM.

On the plus side, this thread (plus some emails) convinced me to get Flyin Miata Fox suspension for my RallyCross Miata!

Changing springs is easy so try it both ways. I never would have guessed that stiff would be good on dirt without giving it a go!

Thanks, guys. I think I'm slightly less likely to throw myself out of this first story window now.

Thank you for the offer to impart some wisdom, Keith. I am tied up with daddy duty for the rest of the day today, but I will definitely reach out to you after the holidays. I do plan to speak with each vendor before making a purchase decision, and you guys are obviously high on my list. It's a little off topic, but this time next year, my winter project will be adding one of your turbo kits to this little Miata.

For reference, my home track is Motorsport Ranch in Cresson, TX. I also visit the other regional tracks: Eagle's Canyon, Hallett, and Texas World, along with making a yearly pilgrimage to CoTA.

Let's keep in mind the goal of this build is to wow students and witness other instructors' shocked faces as I pass them in their "faster" cars. I'm not going for absolutely every ounce of speed on the track, but I do want all that can reasonably be obtained short of ruining it for the street.

It is good to know that FM Fox shocks can take more spring without re-valving. Springs are relatively cheap, and I don't mind experimenting there. I obviously have more research to do, but starting at 550 with the option to move up to 700 is comforting.

Here is what 949 recommends for the NB2 for a track-focused, streetable car.

949 Racing said: We recently setup an NB2 street car just like this. It has what is essentially a Big Grip Kit, minus the bushings: 800/500 Xida, dual spring, billet mount. Racing Beat 54103 front bar Supermiata rear bar Supermiata endlinks ELBJs At 4.5-5" front pinchweld, you should be able to reach -3* camber with the ELBJs. The extra height makes a huge difference in ride quality. We have recently updated our Miata race alignment page and raised all the recommended ride heights. They're good.

The compression nose is what I was thinking of, when I mentioned thinking of Xidas as being more hardcore track-oriented. The FM Fox dyno plot is much softer. I can definitely see how Xidas could be busier.

AutoX is like kissing your sister. Enough of that nonsense!

Just as another data point. I had the FM 2.5 suspension system (~390/310 springs, tokico white shocks, bars) on my STS 97 Miata. It was perfectly good. When I stepped up the prep level and moved to Hoosiers the springs weren't enough to keep up anymore. Doing a couple of track days with that setup on SM7s reinforced my problem. When the grip goes up you really need to balance it with extra stiffness. Tire tech has come so far in the past 15 years, I suspect that's why the race to 1,000 lb springs has become a thing. Now I'm running SM suspension (700/325 springs, bilsteins, eiback bar) and 275 Hoosiers. The rear bar created terminal oversteer so it went away.

If you really want to pick up track speed I'd spend a bit less on the suspension and get R-comps. 275 rubber on a 10" wheel is the business!

Kylini wrote: On the plus side, this thread (plus some emails) convinced me to get Flyin Miata Fox suspension for my RallyCross Miata! Changing springs is easy so try it both ways. I never would have guessed that stiff would be good on dirt without giving it a go!

Too stiff isn't good on dirt, but too soft and bottoming out all the time is even worse. Being stiff enough to keep it from getting into the bumpstops hard all the time and causing spikes in spring rate helps a lot on dirt. And it makes the car more responsive too.

Wow, he really raised the ride heights with ELBJs.

It used to be more like 4-4.25" F/R ride heights. But that was more to get the necessary camber up front.

KyAllroad wrote: Just as another data point. I had the FM 2.5 suspension system (~390/310 springs, tokico white shocks, bars) on my STS 97 Miata. It was perfectly good. When I stepped up the prep level and moved to Hoosiers the springs weren't enough to keep up anymore. Doing a couple of track days with that setup on SM7s reinforced my problem. When the grip goes up you really need to balance it with extra stiffness. Tire tech has come so far in the past 15 years, I suspect that's why the race to 1,000 lb springs has become a thing. Now I'm running SM suspension (700/325 springs, bilsteins, eiback bar) and 275 Hoosiers. The rear bar created terminal oversteer so it went away. If you really want to pick up track speed I'd spend a bit less on the suspension and get R-comps. 275 rubber on a 10" wheel is the business!

I'm too lazy (and cheap!) for the Purple Crack. Tires have to be streetable--even if barely.

In your mind, what does a less expensive, high performance suspension look like?

z31maniac wrote: Wow, he really raised the ride heights with ELBJs. It used to be more like 4-4.25" F/R ride heights. But that was more to get the necessary camber up front.

Yeah. I had already planned on ELBJs. I have always struggled to get enough -camber in the front of my RX-8 without resorting to unhappy compromises. The new recommendation should really help with travel in the Miata.

z31maniac wrote: Wow, he really raised the ride heights with ELBJs. It used to be more like 4-4.25" F/R ride heights. But that was more to get the necessary camber up front.

It's all about travel You've gotta let that suspension move.

Keith Tanner wrote:

z31maniac wrote: Wow, he really raised the ride heights with ELBJs. It used to be more like 4-4.25" F/R ride heights. But that was more to get the necessary camber up front.

It's all about travel You've gotta let that suspension move.

Very true. But even at that height, with those rates, I think the only time it got to the bumpstops was Turn 1 at Hallet where you nearly want the outside tires on the curb as well!