Talk Me Off the Ledge - Miata Spring Rates

I'm not sure exactly what the implications of running more spring in the rear would be for my sway bar setup. Right now there is the Supermiata 14mm rear bar in there and I'm not sure I want any more? Alignment is aggressive, 4.5/2.5 f/r with some toe out up front and toe in in the rear.

I feel like my car is pretty representative of a turbo car that kind of wants to do it all. I think that actually represents a fair number of people.

Maybe I'll start with 550 in the rear and see if it feels like a step in the right direction.

If you increase the rear spring rate, you'll typically want to go to less rear bar to maintain the same balance. A lot of track Miatas don't run a rear bar at all depending on what else is being done with alignment and rates and driver preference. 

Note that Spec Miatas have a required spring and sway bar set, so they are excluded from that generalization. 
 

Moving from 500 to 550 in the rear is a fairly subtle change, I'd be tempted to go to 625 or so with the 750 front if you want to keep the same balance I've been playing with - and no rear bar in that case. 
 

 The stock Fox spring rates are aimed at the "do it all" crowd, going 50% higher is generally more of a track-biased setup. 

@stevedallas    I'm gonna take a guess you're in DFW. If you ever find yourself near Austin, you're welcome to drive my '95. It's almost exactly your use case. Xida race setup on 15x9, 245 RS4's

Yes, it's unbelievably, incredibly good on street and track. Believe the hype. Surprisingly compliant even over large potholes/railroad tracks/etc. I currently have 5 cars, and the miata is the 2nd most comfortable ride behind my Prius. I believe Xida makes a setup with slightly softer spring rates as well. I've never driven an FM setup so I can't comment there.

I love the Penske Spec Miata coil-over suspension on my '90.  It takes track bumps and curbs way better than the old Bilstein Spec Miata coil overs, plus they are rebuildable by Penske.   It's a great track set-up IMO

I've never driven the car around town so I don't know how it would be on the street.

Better than the old Bilstein SM is pretty faint praise :)

I've driven a few variants of those SM-based Penskes on the street. They're not back, but their hardware is designed for minimum isolation so they're pretty noisy. Like "did I tighten all the bolts?" noisy. Definitely a very nice track setup.

I think the Fox ride as well as the Xidas on the street but with a calmer front end. The tradeoff (on the NA/NB) is a little less ferocity on turn-in, the Xidas are all about loading up that outside front. More travel overall, too, which helps on stuff like big crests taken at speed.

fornetti14 said:

I love the Penske Spec Miata coil-over suspension on my '90.  It takes track bumps and curbs way better than the old Bilstein Spec Miata coil overs, plus they are rebuildable by Penske.   It's a great track set-up IMO

I've never driven the car around town so I don't know how it would be on the street.

I'm still running the Bilsteins on my SM and I'm not a fan.  I've never liked that setup. The shocks aren't great and the spring rates are even worse.   Their only saving grace was that everyone who didn't cheat and have them re-valved was running the same setup.

I'll try 625 in the rear and take the bar off... And report back.

I've got a 2006 Sport 6AT with 165k on the car and 65k on a stock 2.0l engine from a 2013 Club Sport. Stock everything.  I still drive it like I stole it, and enjoy pushing it hard through lower speed (>50mph) corners.  I'll probably never put money into FI, though I might upgrade the exhaust someday.  I always run summer tres.  Currently the Firestone Firehawk Indy500 on stock wheels 205/45ZR17.

I want to lower it for appearance (currently sits up like a 4x4) as well as lowering the center of gravity for overall performance, and I want to make it handle as best I can w/o spending big bucks.  It's my DD and I love it!

I don't want to "cheap out" on crap coilovers but don't want to spend $3k on them either.  What are the best choices here?

Oh, and if it's recommended, I'll change out the sway bars too.  ;-)

Thank you in advance.

Note that most of the numbers and comments here are based on the NA/NB chassis.

In your case, I'd run a Flyin' Miata Koni Stage 2 kit. FM springs, Koni Sport shocks, FM sway bars. Gives a really good daily driver setup that's got solid performance, and it's got enough spring rate to keep you off the bumpstops unlike most appearance-based "lowering springs". The sways aren't required to make the springs work, but they're a big part of street fun because they'll make it corner flatter and turn in better. They also let you adjust the handling balance to suit your preference easily.

Disclaimer: I work at FM and am the person who signs off on those suspension parts. So of course I think they're the best choice :) If I didn't, I wouldn't have signed off on them...

Glad to see this resurrected thread, lots of good info. With regard to when is spring rate too much?... I'm trying to understand when does spring rate overwhelm tire choice? My use case is a "new to me" NA6, that has the 14-inch BBS rims that I want to retain for the street. This car will see it's fair share of HPDE days. My dilemma is I'm willing to pay for the FM Fox coilovers, and run different wheels for the track, but will the 550/375 lbs springs overwhelm a 185 or 195/60-14 summer performance tire? Track days aside I more often run this through some awesome back country roads, some a bit bumpy, and I want to max out the fun without putting it in a ditch because the tires can't cope. Are the Fox spring rates too high or would I be better off with the Koni Sports that use a lower 318/233 rate? Is the Fox vs Koni valving compliant enough for spongier tires? With or without stiffer sway bars, that also increase effective rate. (@ Keith Tanner, I'd love your input as you may be the only one here with actual experience with these specific set-ups!)

I haven't spent a lot of time with Foxes on 185 "summer performance" tires, although I have run them with 195 winter tires :) Note that sidewall height isn't the only indicator of how spongy a tire is, I used to have a set of Kumho 711s on 17" wheels and some RT215 Azeniseseses on 14" wheels, and the Kumho had much more sidewall compliance. Extreme example but it's real and it does illustrate the point.

In my experience, the tires won't be overwhelmed by the spring rate. Shock behavior has a lot to do with the compliance you're looking for, and the way the Foxes are valved they don't use the shock as an air spring the way some other setups (hello Bilstein) can do. This means they feel like the springs are softer than they are.

I've run both on my street car, including track time. Nothing wrong with the Koni/FM setup, and I think they've got a slight edge in ride quality. But the Foxes work so well on track and certainly don't abuse you on the street. They're both good options.

In reply to Keith Tanner :

Thanks Keith, that was very helpful perspective!