Bay Area Miata Drivers
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by nick
Looking ahead and looking back on the Miata, sports cars, clubs, and BAMD. Plus of course updates on my Miata.
Entry # 18 (23,926 Views) Posted on July 9, 2011
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The Definitive Suspension Blog
I thought I might share my thoughts on Miata suspension upgrades, since so very little has been written about it over the years. Okay, maybe more than a little, but only if you count all the books, magazine articles, and billions of forum posts on the Internet. 
If you've read more than a few of these reputedly informed opinions on the Internet, one thing that seems immediately clear is that the stock Miata suspension sucks, and that anyone with a stock suspension risks launching their Miata into a fatal skid at every turn in the road. In declaiming the design of the Miata suspension, these self-proclaimed suspension gurus have decreed that the engineers at Mazda, with their hundreds of years of combined training and experience, got it wrong. 
Giving these people the benefit of the doubt (which I seldom do), I think we can agree that Mazda designed a pretty good sports car suspension for most of us, but maybe didn't go quite far enough for the type of person who would be inclined to have an opinion on the subject. Having done a little suspension work on my own '97, I of course know as much as all the other self-proclaimed suspension gurus. However, the other gurus have one advantage over me. They don't have to actually drive a Miata with a particular suspension setup in order to know how it rides and handles in every situation and at every suspension setting. I haven't figured out how to do that yet. Maybe I need to meditate more. Okay, I'm probably getting a little too harsh going on about self-proclaimed suspension gurus. Sorry. Let me continue. 
At some point in your Miata ownership, you're probably going to want to do something with the suspension. This can happen for lots of reasons. You could feel like the car doesn't ride the way it used to, and it might be time for new shocks. You could be looking at getting involved in motorsports activities. You might want the car to sit a little lower. Or maybe you just want more grip. All of these things can be achieved through suspension upgrades. The trick is figuring out which ones. What you buy, what you throw away, and what adjustments you make can be a tough decision, especially with all the billions of options out there. 
I've said it many times before, but of course that won’t stop me from saying it again: There is no single perfect Miata suspension. If there was, we'd all have it, and that would be the end of it. Instead, there are many states of compromise. Everybody wants the ultimate in grip, handling, and a smooth ride, but you can't have all three. The best we can do is try to compromise for the type of driving we do most. To that end, we can try to at least come up with optimal suspensions for daily driving, autocross, track, and spirited back roads, both bumpy and smooth. 
Suspension setups can be broken down into five basic categories -- spring rates, shocks, sway bars, ride height, and alignment settings. Obviously there are many options within each of these categories, including vendor options. Putting those aside for now, the chart below contains my own ideas about what suspension upgrades you should consider, based on the type of driving you want to do. I've tried to avoid vendor considerations and prices, because for just about any type of Miata suspension there's a cheap way to go, even if it means buying used. 
type of drivingspring ratesshockssway barsride heightalignment
Daily driver<300 front 
<200 rear
1) Illumina2) AGX
3) Bilstein
FM or RB front
FM or RB rear
>=13" front
>=13.5" rear
-1.0 front
-1.5 rear
Track>300 front
>200 rear
1) Koni Sports
2) Illumina
3) Bilstein (revalved)
FM or RB front
FM or RB rear
12"-12.5" front
12.5"-13" rear
-1.5 front
-2.0 rear
Autocross>420 front
>280 rear
1) Koni Sports
2) Bilstein (revalved)
FM or RB front
stock rear
11.5"-12" front
12"-12.5" rear
<=-2.0 front
<=-2.5 rear
Spirited smooth roads300-450 front
200-300 rear
1) Illumina
2) Koni Sports
3) AGX
FM or RB front
FM or RB rear
12"-12.5" front
12.5"-13" rear
-1.5 front
-2.0 rear
Spirited rough roads200-320 front
150-240 rear
1) Illumina
2) Bilstein
3) Koni Sports
FM or RB front
FM or RB rear
12.5"-13" front
13"-13.5" rear
-1.5 front
-2.0 rear
Springs and Sways 
One thing you can see from the chart is that every type of driving benefits from aftermarket sway bars. These are relatively inexpensive to boot. I don't want to get too technical about the purpose or function of sway bars, but you often see on the Internet a lot of confusing and sometimes conflicting advice about sway bars. The reason it's confusing and conflicting is that a lot of it is just plain wrong. I don't know how some of these myths got started, but they keep getting repeated, and someone once said if you repeat something long enough, it becomes the truth even if it's not true. 
The main thing you need to know about sway bars is that they act like helper springs in a turn. They don't act like helper springs under braking or acceleration, but they do in turns. A stiffer sway bar is just the same as stiffer springs. Running a stiffer sway bar up front is the same as running stiffer springs in front, and running a stiffer sway bar in back is the same as running stiffer springs in back. But only in turns. Stiffer springs are good in turns because they keep the car from leaning too much, which keeps the tires from leaning too much, which helps them stick better. 
Stiffer springs also mean a harsher ride. It's one of the compromises we make for better grip and more responsive handling. So we might want to know if sway bars act like helper springs on bumps. They do, but only about half as much as they help in the turns, and sometimes less. The result is that sway bars give us stiffer springs where we want them, in the turns, but not when we don't want them, on the bumps. 
A lot of sway bar talk revolves around what size bars to run front and rear, and whether to run a rear bar at all. This talk usually centers around the dreaded front roll couple percentage (FRC%), a concept that all self-proclaimed suspension gurus understand implicitly. FRC% is based on the ratio of spring rates front to rear, and it's based on total spring rates, including springs, sway bars, and bushings. A higher FRC% means the front is stiffer, a lower FRC% means the rear is stiffer. A stock Miata has an FRC of around 58%, and it's usually a good idea to keep it there, or maybe a little lower for more nimble (i.e. tail-happy) handling. 
So let's consider the rear sway bar question. The reason we get bigger sway bars in the first place is because we want stiffer springs in the turns without sacrificing ride comfort. So it just doesn't make sense to get a big bar for the front only. We want the same advantages at the rear of the car that we enjoy in front. The only exception to this is autocrossing, where bigger rear bars are sometimes against the rules, and can also reduce traction coming out of those tight autocross turns. The way I figure it, all of this no-rear-sway-bar nonsense got started by 1) autocrossers or 2) some guy who had a bad set of aftermarket springs and found his car handled better without the rear bar, then posted it all over the Internet. 
So if we're keeping the stock springs and only getting aftermarket sway bars, and we want the same friendly FRC% that we have now, we add helper springs (sway bars) both front and rear. Adding only the front bar will significantly increase the FRC%, and the car will plow like a pig. So we get both. As it turns out, FM sway bars (for example) at the recommended settings do decrease the FRC% slightly, but it's barely enough to notice, it just adds a little more nimbleness. 
If we're getting aftermarket sway bars and changing springs at the same time, we'll choose our spring rates so that the FRC% remains close to stock. That way we get to use bigger sway bars front and rear. If for some reason we can't find the spring rates we want, or we buy a package (e.g., coilovers) that has a lower FRC% than stock, only then would we consider running a front sway bar only. But that would not be optimal. 
Here's something important to keep in mind. FRC% isn't the only thing that determines whether your car understeers or oversteers. Tires, tire pressures, and alignment settings affect it as well. Generally, a performance alignment reduces understeer, so if you get an aggressive alignment and you don't want your Miata to be any more tail-happy than it already is, you need to compensate with an FRC% that's a few points higher than stock. You can make those kind of changes with sway bar adjustments, if you have adjustable sway bars. 
Shocks and coilovers 
In Miata parlance, a coilover is a shock/spring combination with a moveable spring perch that lets you adjust the ride height at each corner. I can't say whether or not coilovers are superior to regular springs and shocks, but to me the only real advantage of coilovers is height adjustability, and that's not a big one. Setting ride height is cool, but it's unlikely you'll do it much, especially when you add the cost of an alignment and corner-weight session each time you do it. One problem I do have with coilovers is that you're buying the shocks, springs, bumpstops, and mounts specified by the vendor. They may work great together, but they're going be the vendor's idea of a good time, and maybe not yours or mine. If you can find a coilover vendor who will let you specify spring rates, you're better off. 
I particularly don't like the lower-priced coilovers. They're very popular, but I think that's mostly among drivers who's top priority is lowering the car. The shocks they use aren't usually adjustable and I don't think they'll last very long, maybe 40K tops. Some people point to the fact that Flyin' Miata sells bargain coilovers, and if Flyin' Miata sells them they must be good. I actually think Flyin' Miata sells them to make a profit, and doesn't really have a lot of respect for them. 
I prefer mix and match suspensions over coilovers. Springs are available from a variety of sources in a lot of different rates, and you get to choose. You also have a lot of great shock manufacturers to choose from, and the shocks in the chart are just the more popular examples. Some shocks are adjustable, and adjusting them can change the handling of a Miata dramatically for different types of driving. Among the adjustable shocks, Tokico Illuminas are generally considered high-quality and comfortable for daily driving, and even spirited driving with the proper adjustments. Konis aren't considered to be as comfortable, and they're not as adjustable, but they have a good damping curve for autocross and track, especially when the rebound damping is turned up. I've had both of these shocks on my Miata at one time or another, and I tend to agree with this consensus. 
Another popular aftermarket shock is the KYB AGX, which is sometimes described as a low-priced Illumina. I've driven a car with AGXs and found them very comfortable. Bilsteins are also really popular for the Miata, in part because they're standard equipment on some Miatas, and also because they use a monotube design. Monotube shocks can have a slight performance advantage over concentric tube shocks if they're properly designed, however they're also more prone to failure from external damage. Personally, I'd be more concerned with how well a shock works than how it's designed, but that's just me. Bilsteins aren't adjustable, but that hasn't stopped people from changing the damping by swapping out the internal valves. Not as easy as, say, turning a knob on the side of the shock, but there are people who do it. I find it slightly amusing that Bilstein proponents who downplay the need for adjustability in a shock are the first to send their Bilsteins out for revalving when they change springs. 
Probably the most important thing about picking shocks is making sure they have enough damping for the spring rates you're running. Illuminas are fine with stock springs on the lower settings, and they can handle springs up to about 400 in/lbs if you turn them all the way up. Springs much stiffer than 400 lbs. will feel underdamped, like the shocks are wearing out. Konis are less able to handle the really stiff springs because they're only adjustable in rebound. You can use them with 500 lb. springs, but they're optimal in the 300 lb. range. Because of the lack of jounce adjustment, stock springs feel overdamped with Konis, which isn't a big problem but it makes them ride harsher than other shocks. Konis are also available in a Race version, which have a lot of adjustments on them and can handle almost any spring rate. However they will pretty much blow up anybody's suspension budget. 
These aren't the only options of course, but they are the most popular. Some people try to keep costs down by using a cheaper brand, or going with a lower-priced shock from one of the popular brands, like Tokico Blues instead of Illuminas. This seldom ends well. You're better off buying used. All of these shocks are good for at least 50K miles, and some a lot more. 
Ride height 
I like to think the car's height should be set for the best compromise of ride and handling. Many people feel the height should be set by how the car looks. The numbers in the chart above are not based on looks, and if you want to go lower that's fine, so long as you keep in mind that the other recommendations in the chart probably won't work for you either. 
Lowering your Miata has a couple of positives, and a long list of negatives. Lowering the car affects ground clearance, wheel travel, camber geometry, wheel clearance, roll centers, and bump steer. The negatives don't get too bad until you go below about 12.5" front/13" rear. I like to think that Mazda designed everything about the Miata with the idea that it would sit a certain height above the ground, and not two inches lower. For an autocross or track-only car, the negatives aren't as important or they can be corrected, but on a daily driver you'll notice them every day. 
Unless you're looking for the ultimate in grip and you don't care about tire wear, I wouldn't get cute with alignment settings. Anything negative up front is an improvement over the stock settings, and setting the rear about half a degree more negative than the front is a good balance. I like zero toe-in all around. It's simple, predictable, and easiest on the tires. Some autocrossers prefer a little toe-in or toe-out in front or in back, but I'm not really sure they all agree on which tire should point where. There are a couple of "boutique" alignments floating around the Internet, and if you think it's cool that your alignment has a name, go for it, but I personally think it's unreasonable to assume that one alignment can work for everybody and every suspension. 
Other Suspension Considerations 
Something that's not in the chart but should be considered with any upgrade on an NA Miata (90-97 model years) is a switch to NB shock mounts. Some aftermarket suspensions include mounts, which is great, but for any other upgrade it's really worthwhile to spend another $150 for NB shock mounts and the related hardware. You'll never get an NA suspension to work as well as an NB no matter what you do with bumpstops. 
Speaking of bumpstops, which I'll try to do without getting on my soapbox again, stock NB bumpstops will work with just about any suspension you put on an NB, or any NA with NB suspension hardware. It gets tricky on an NA with NA mounts, at least in back, because the car wasn't given a lot of suspension travel to begin with and it wasn't designed for long, compressible bumpstops. So you see a lot of confusing and sometimes conflicting advice about bumpstop size and length on the Internet. You can avoid all that by just switching to NB hardware. 
No one is really sure when Miata suspension bushings wear out. In the early days, before NBs and NCs, bushings were supposed to get pretty tired after 60-80K miles. Nowadays they're said to work fine even after 200K. The fact that they're a PITA to replace may have something to do with the higher estimates. 
If you're not sure about replacing your bushings, I wouldn't. They're really expensive. A cheaper option is polyurethane bushings, and that's an option for a track or autocross car, but you'll feel them on every bump. They're not jarring, but they're not exactly supple either. A good compromise is the Mazdaspeed high-density rubber bushings. They're just like stock except the rubber is about 40% stiffer. They're also just as expensive as stock bushings. Not as harsh as polys, but you feel the difference. You can tell there's still a little rubber in the suspension, but it feels pretty thin. 
So what do you get? 
To be honest, at this point I wouldn't have a clue. There really are hundreds of options, and it seems like every few weeks someone comes out with something new. The competition for your suspension dollars is fierce. Two things I think are very important when you're contemplating dropping serious cash on new suspension bits. The first is to drive a Miata that has the suspension you want. Try to drive it in lots of different situations. The second is to ignore any review of the suspension you want. I have read hundreds of suspension reviews and have yet to find one that doesn't claim that their new suspension is the finest ever made for the Miata, and worth every penny they paid. 
In the end, I think you have two ways to go. You can go with one of the tried-and-true spring and shock combinations, which would include some of the low-priced coilovers, or you can go with one of the "boutique" suspensions, like the high-end coilover setups. In either case it's mostly going to boil down to the numbers in the chart, and those aren't fixed in stone. You can set your Miata up as a full-out autocross car and drive it daily on the street, or you can drive your street creampuff at an autocross. As long as you're having fun, I think that's all that really matters.
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Comments (newest first)
2011-07-20 17:57:12 from nick
To answer David's question, the difference is that the front wheels also steer the car, and more camber up front when the wheels are turned has a bigger effect than more camber at the rear. The half-degree difference front-to-rear isn't an absolute requirement, but it's been found to work best.
2011-07-20 11:15:56 from David
I see a lot of people recommend the alignment for Miata the same way, the rear camber should has about half degree more negative than the front. What do think about the reverse (front camber more negative than rear)? Would you recommend that? And the difference is?
2011-07-15 19:59:26 from ada
What a great blog! I just did a suspension upgrade for a friend, DD and track use. I went with Koni Sports & C coilovers 300+/250s. Very nice ride on the street, track should be good novice -> low intermediate. You just confirmed what I thought!
2011-07-10 14:48:43 from alex
I know I said I liked how my Miata looked when it was really low, kinda bad-ass, but that was just the bonus (at least I thought so!) because I REALLY like how well it transitioned, like it was on rails. Of course that could have been a result of any number of concurrent tweaks, including FM sways. Though those are still on there and it doesn't feel quite as crisp as it did. But I also don't miss the tires rubbing the fender liners. . .So yeah, IDKWIATA!
2011-07-09 21:21:58 from alex
Thanks Nick! 
+1 on the having fun with the car, and I would add that you should have fun modding your suspension too. Don't take it too seriously, expect to make mistakes and gain experience. My brother says "experience is what you get when you didn't get what you wanted." If a setup you paid too much for isn't working, don't worry, there's some other sap, er, guy or gal who will buy that stuff from you. Not at full price, it's used after all, but for a price that will take some of the sting out of buying something else.