AGX shock with RacingBeat Springs, FM swaybar on the left.

Introduction
Suspension tuning is one of the last “dark arts” in automotive technology that has never really been perfected. And people have so many different philosophies when it comes to properly tuning a suspension that there may never be any real consensus on which way is the best way to build and tune a suspension.
Engineers spend hundreds of hours finding the right balance between comfort, handling, and grip. Often they have develop and fine-tune this package with a less than ideal budget to let them truly go all-out and create a suspension that is world class.
Sometimes they come up with a real winner, and other times they fail miserably and only deliver 1 or 2 out of the 3 goals.

The Miata is a surprising and refreshing example of what happens when engineers manage to work within their budget to create something that is almost perfect straight from the factory.

So how do we improve upon something that is so downright good? That is the question I asked, and the subject I chose to explore using my 91 Miata as the guinea pig.
I’ve come away from this experiment with a much clearer understanding of how and why the Miata’s suspension works the way it does, and what compromises one has to make to attain a better handling or riding Miata.

This page documents all the various suspension modifications I have made, outlines some of my goals I had before starting, and hopefully will be useful to someone.

The page starts out with a brief description for each suspension componnent and what it does, and further down the page I have written reviews on how the car handled and performed with a paticular part or parts installed.
You can start at the top and read down or you can jump to a section by clicking the link below.

Goals for Suspension
AGX Shocks
Swaybars by Flyin'Miata
Springs by RacingBeat
Shock mounts by Flyin'Miata
FCM 46MM Bumpstops
FCM 54MM Bumpstops
1: Stock suspension
2: KYB AGX, FM Swaybars.
3: KYB AGX, FM Swaybars, RB Springs.
4: KYB AGX, FM Swaybars, RB Springs, RB Endlinks, FM Shock Mounts.
5: KYB AGX, FM Swaybars, RB Springs, RB Endlinks, FM Shock Mounts, FCM 46mm Bumpstops.
6: KYB AGX, FM Front Swaybar, Stock rear swaybar, RB Springs, RB Endlinks, FM Shock Mounts, FCM 46MM bumpstops
7: KYB AGX, FM Front Swaybar, Stock rear swaybar, Stock Springs, RB Endlinks, FCM 54MM bumpstops
Alignment Numbers
Summarization and tips

My Goal for the Suspension setup

I had three very simple goals for setting up the suspension the way I did.
1: The one thing I absolutely loved about the Miata was it's handling balance.
That is something that Mazda got right from the factory and something I wanted to preserve.
I did not want to mess up the balance by going with too stiff of a spring or swaybar setup in either the front or the rear could really change the balance for the worst.
2: I wanted to preserve or possibly even gain a better ride.

3: Miyoshi is a Street car first and a track car second. So any and all modifications have to be livable for a daily driven vehicle.







Part List and description

KYB AGX 8-way adjustable shocks

The AGX shocks are adjustable shock absorbers that have 8 settings that adjust for both compression (or "bound" if you prefer) and rebound.
The purpose of an adjustable shock is to provide better handling and ride quality by adjusting for road conditions and driver preference, and to increase compression and rebound to control stiffer springs.
The standard valving for the AGX has lower compression then a stock shock, but higher rebound. Unfortunately, this means the AGX does not work as well with stock spring rates as a stock shock would, and can have a negative impact on ride quality over rough sections of road.

A good refference for the AGX's bound/rebound rates, is this chart from Fat Cat Motor Sports: Shock Dyno Comparison Chart.

The big issue with the AGX's as you can see in the graph, is how disproportional the compression and rebound rates are. In fact, the compression damping doesn't even begin to approach the stock shock's compression level until you get to the 8'th setting, while the rebound has been piled on to the point where it is easily overpowering a stock spring.
Most of this data was unknown to me at the time that I purchased the AGX shocks.
And keep in mind I'm not saying the AGX is a bad shock, for the price it rides fairly well on the lower settings, handles very nicely, and holds the road better then the blown shock absorbers that more then likely are on your Miata right now.
I should also note that my AGX's have been very durable, and have lasted well into the 90,000 mile mark including much autocross abuse, and still feel strong.

I would however recommend something that is stiffer then a stock shock that has higher compression and adjustable rebound, like a Konis or Tokico Illuminas (the Illuminas adjust both compressiona dn rebound like the AGXs, but have better damping curves for better ride and handling.)
The AGX's high rebound rate does allow them to work well with mild lowering springs in the 200-250 lb/in range.








RacingBeat Springs (Mixed sets)

Spring Location Spring Rate (lbs/inch) Spring Type
Front 226 Race - Linear
Rear 113 Street(new) - Linear
RacingBeat (RB) still had a few of the front Race springs in stock.
At 226 lbs/inch (front springs), it seemed like a good beginner spring that would give a modest bump in spring rate from the stock 168 lbs/inch (front).
I wanted to keep my larger rear FM swaybar connected, and this meant I needed to preserve the front/rear roll couple balance.
So I went with the rather conservative 113 lb/inch (up from 97 lb/inch stock) rear springs that RacingBeat is offering up as there new street spring.


One of the big advantages to choosing the RacingBeat springs was that now I had the proper spring rate (220) to handle the increased rebound rate and lack of compression damping that the AGX shocks have. I heard that the Race springs would lower about 1 inch in the front and the rear springs would also lower 1 inch in the rear.
In the end once the springs had finally settled, my ride height ended up at 12.2 inches in the front and 12.5 inches in the rear. Stock ride height was 13.0 front, and 13.5 rear.







Flyin'Miata Shock Mounts for the Rear

The mounts raise the shock shaft mounting point without moving the spring seat location, allowing the suspension to gain 1 inch of bump travel and 1.25 inches of wheel travel. In return you will lose about 1 inch of droop travel.
More travel means a more compliant and comfortable ride as the suspension is no longer bouncing off the bump stops.
Because the shock haft mounting point is raised and the spring seat is the same as stock, these new mounts will not lower the car's ride height.

The FM mounts come with 2 new bumpstops, 2 new dust covers designed to fit over the new bumpstops, 4 bearing pieces that have to be fitted to the inside of the mounts (they snap into place), and of course 2 purple and shiny shock mounts. Installation was very straight forward, and the mounts came with some very easy to read instructions for new comers to the suspension swapping party.
A big problem I noticed with these mounts is that unlike the OEM mounts, the mount opening is a perfect circle instead of being D-cut as it is on the OEM mounts, and as a result the shock shaft can spin when you are trying to torque the lock nuts in place.
Only way around this issue is to use an impact wrench.







Fat Cat Motor Sports 46mm MCU bumpstops.

After the RacingBeat springs had settled into place, the ride height was unbearably low for a car sitting on stock un-trimmed bumpstops on the front suspension.
The result was a choppy ride and unsettled handling characteristics, and a mid-corner bump was all that was needed to send to the front end skittering for traction at 8/10ths.
The solution? Get the car off the bumpstops! To accomplish this task, I turned to Shaikh at FCM, and a set of 46mm MCU linear progression bumpstops, known for adding suspension travel and providing a softer transition onto the bumpstops than the rubber OEM pieces.
These bumpstops slid right over the shock shaft with no problems whatsoever, the same couldn’t be said the foam stops that came with the Flyin’Miata rear shock mounts.







Fat Cat Motor Sports 54mm MCU bumpstops.

With the thought of taking my car back in E-stock dancing through my head, I decided to swap in a set of stock 91 springs and remove the FM mounts and rear swaybar.
I decided to go ahead and address the two major shortcomings of the stock Miata’s suspension right off the bat.
1: Lack of suspension travel.
2: Awful ride and handling when you use up the suspension travel and go straight to the OEM rubber stops.
To address these issues, I once again turned to FCM’s bumpstops, this time opting for a set of the 54mm stops without the dust boots.
And the result of this upgrade? I now have a NA that now handles and rides closer to an NB.
I was now using the springs during hard cornering and to absorb bumps and pot holes instead of the bumpstops, which makes for more predictable handling and much better ride quality.
The few times I have come in contact with the stops, the transition from spring to bump stop is almost impossible to detect, it’s like adding more spring length.







1.0: Stock Suspension

The Miata comes with a good suspension setup straight from the factory, with the only weak link in it's armor being the OEM rubber bumpstops and their rather "un-predictable" nature at the limit.
The handling balance is exceptional, favoring a "tail-led" aproach to taking a corner.
Pros
Cons
  • Fairly soft ride
  • Nicely balanced
  • Fun and easy to drive on the limit
  • Good steering feel and feed back
  • Despite soft nature of suspension, it can be upset rather easily by mid-corner bumps, and it can downright hurt when you bounce off the OEM bumpstops.
  • Shocks are only good for 40,000 miles.







2.0: KYB AGX Shocks and FM Swaybars

In order to keep up with my friend and fellow Autocrosser Jason G at the track, I knew I was going to have to beef up more then just the shock absorbers.
But the question was how to do it?
After exhaustive research into the age old debate of Springs VS Sway bars, I ordered the AGX shocks off ebay and a set of Flyin'Miata swaybars.
Both packages arrived at the same time and the shocks went in first followed by the sway bars the next day.
Pros
Cons
  • 8-way adjustable damping allows you to adjust the shocks stiffer for Autocross or canyon carving.
  • Swaybars are adjustable for various situations and surface conditions.
  • Chassis feels more connected to the road when at speed
  • Decent steering feel and feedback.
  • Flatter cornering, faster transitional response (slalom situation)
  • Preserved the handling balance nicely
  • Shocks should last well into the 100K miles range
  • Good blend of performance per dollar for anyone on a budget
  • Steering lost some feel and some of it's delicacy with the swaybars.
  • Rear end is more prone to stepping out.
  • Slight increase in NVH (noise vibration harshness) from thickier swaybars not allowing completely independant suspension movements anymore
  • Could not find a good all-round shock setting for daily driving in combination with these swaybars.
  • Lack of travel coupled with the stiffer rear swaybar could lead to snap oversteer if a mid corner bump was encountered fast enough.
  • Not enough Compression Damping from settings 1 to 3, and too much rebound from settings 3 to 8.







3.0: KYB AGX Shocks, Flyin'Miata Swaybars, RacingBeat Endlinks, RacingBeat Springs.

I'm not going to say the ride was bad, but...
The only way to try and keep the rear suspension off the bump stops was to turn the shocks up to about 6 or so to increase the compression rate.
Worked great for highway driving, but the second you were back on a rough city street it was a chiropractor's wet dream.
Pros
Cons
  • Dive and squat were reduced tremendously.
  • Transitional response time was reduced even further, felt fantastic in medium to high speed transitions.
  • RB End links helped to reduce some of the NVH coming from the front swaybar, and help to keep the bar from binding when set correctly.
  • Ride harshness increased significantly both front and rear.
  • The lack of suspension travel in the rear was reduced even further with the springs
  • Wet weather traction would suffer from either running the shocks high to keep off the bump stops, or smacking the bump stops because the shocks were too soft. No win scenario.
  • Car is starting to exhibit more bump-steer than it had with the stock springs.







Version 4.0: KYB AGX Shocks, Flyin'Miata Swaybars, RacingBeat End links, RacingBeat Springs, Flyin'Miata Shock Mounts

After tolerating the harsh ride from the springs as long as I possibly could stand,
I came to a conclusion that either I needed to increase the rear suspension travel or get rid of the springs.
Guess which one I chose...

Thanks to the increased travel in the rear suspension from the FM mounts, I was now able to turn the shocks down to a more modest and more appropriate setting of 3 all around without the fear of bouncing off the bump stops with every surface imperfection.
Pros
Cons
  • Ride quality became much smoother, especially over rough roads
  • Rear suspension is less bothered by mid corner bumps
  • Tail slides are now even easier to prevent when needed, and much easier to control when you want to have some fun
  • The FM mounts I've found have a tendency to "clunk" when you hit a bump just right.
  • The bumpstops provided by FM have to be cut for your needs.
  • The bumpstops feel like a good improvement over stock, but are still harsher then a set of FCM stops.
  • Front suspension still lacks the travel it needs.







Version 5.0: KYB AGX Shocks, Flyin'Miata Swaybars, RacingBeat End links, RacingBeat Springs, Flyin'Miata Shock Mounts, FCM 46mm Bumpstops

With the rear of the car pretty well sorted, I turned my attention to the front. The FCM 46mm stops provided the travel needed for the front, but bumpstop engagement was still inevitable under hard cornering or in an autocross situation. Still the car was more predictable in the front end, and this setup rode decently, and the car handled well, still favoring a tail-led corner exit.
Pros
Cons
  • Ride quality became much smoother still.
  • Front end feels more connected to the road, not as easily upset by mid-corner bumps.
  • Ride quality while being imrpoved, still did not have the amount of compliance I desired.
  • Tail-led aproaches to the corner are fun, but can get tiresome after a while. Especially when autocrossing.







Version 6.0: KYB AGX Shocks, Flyin'Miata Front Swaybar, Stock Rear Swaybar, RacingBeat End links, RacingBeat Springs, Flyin'Miata Shock Mounts, FCM 46mm Bumpstops

This was easily the best riding/handling combo I had with the lowering springs in place.
I removed the 5/8ths rear FM swaybar and went back to a stock bar. The result was a much more compliant ride, and the tail end now stayed planted much better on corner exit under power.
I was actually kicking myself in the head for not doing this little step backwards sooner.
The extra roll stiffness provided by the rear springs was more than enough to compensate for losing the thicker rear bar, and the ride and handling improvements were definitely worth it.
Pros
Cons
  • Ride quality was easily the best out of all my previous setups.
  • The rear tires stay planted better under power, especially in a tight/slow corner.
  • This setup provided the best transient response, and the best cornering grip while on the lowering springs.
  • Handling balance felt more understeer biased, but still felt great.
  • Ride still has room for improvement, and the lack of travel provided by the springs is a bit annoying.
  • Ride height is at it's lowest point, making speed bumps a pain in the rear.
  • Bumpsteer is at an all-time high, providing some interesting kickback through the wheel.
  • The shocks feel like they are controlling the springs, but initial impact when you hit a bump is still greater than it was with the stock springs.







Version 7.0: KYB AGX Shocks, Stock 1991 Springs, Flyin'Miata Front Swaybar, Stock Rear Swaybar, RacingBeat End links, FCM 54mm Bumpstops

After a very successful season in C-stock driving a bone-stock Mazdaspeed Miata, I decided to put my car back to E-Stock trim for next year’s Autocross season.
This setup is my current setup, and it is easily the best blend of performance, handling, and ride comfort that this car has ever seen.
The FCM stops provide extra travel over the OEM rubber pieces, and the result is the car is now using it’s springs to corner on and absorb bumps with rather then the bumpstops.
Pros
Cons
  • Ride quality is at it's best.
  • Handling is more predictable in nature, cornering grip is slightly less than that of the 6.0 setup, but that is due to not running as much camber with this setup.
  • The suspension finally has the travel it needs on all four corners. making the above two points possible.
  • No bumpsteer is present.
  • Car corners fairly flat thanks to the big front bar.
  • Rear tires stay planted through a corner under power.
  • Not as fast to responde as the 6.0 setup, but otherwise, aboslutely no drawbacks.


My Alignment Numbers

A good suspension setup is only as useful as the alignment you perform afterwards to tune the basic handling balance of the car.
I make it a point to always set my base handling characteristics with alignment settings, then fine tune the handling bias to under-steer, over-steer, or as neutral as I can get using shock, swaybar, and tire pressure settings.
Here are the alignment numbers, remember that these numbers MUST match on each side.

Camber Castor Toe
Front
-1.3 4.8 0 degrees
Rear
-1.7 Not applicable .20 degrees of toe IN.

This alignment provided me with neutral handling base with enough negative camber to keep me from getting abnormal wear at the track.
I'm a pretty aggressive driver, so tire wear is even across the tires despite how much camber I'm running.





Summarization and tips.


This experiment has been a wild ride. It's taken a little over 4 years to try out all of these different setups and see how they did both on the autocross track and out in the real world.
In the end, I ended up almost right back where I started, with a relatively stock configuration, but with allot more knowledge about what to do and what not to do with a Miata’s suspension setup in the future. And below is a small summarization of what I’ve learned:

1: TIRES This page is mostly about suspension talk, but there is one VERY important part of the handling puzzle on your car that matters more than ANY shock absorber, spring, bumpstop, or swaybar you choose to add to your car, and that piece of the puzzle, is the tires you choose.
The best suspension setup in the world is useless without a good set of tires.
I recommend picking up a set of high performance tires before you do ANYTHING to the suspension.
I recommend the following tires:
  1. Bridgestone RE-01
  2. Falken Azenis 615
  3. Hankook RS2
  4. Toyo T1-R

Those three tires above are easily the best high performance rubber for the street you can buy, and all three come in Miata friendly sizes and are fairly easy to find.

2: ALIGNMENT. Just like tires, a good or bad suspension is useless to you if you are running too little negative camber or too much toe-in or toe-out.
Check my alignment section above to see a high performance alignment.
For street driving, around –1.0 degrees of camber in the front and –1.5 degrees in the rear should provide a nice sport handling nature and not show any excessive wear.

3: The stock Miata is suspension travel limited, and re-using your old OEM rubber pieces or buying new ones are a downright retarded thing to do. Especially given the whole host of foam and MCU replacements available on the web (and all for less than the cost of the OEM bump stops!)

4: If you want flatter cornering without a heavy ride penalty, or if you are looking to help keep the rear tires planted under hard cornering, upgrade the front anti-swaybar only.
My preference is for a slightly larger than stock front bar (7/8ths” if you own a 90-93 1.6, and 1” if you own a 94-2005 NA or NB 1.8.)
This bigger bar will help to keep your inside rear tire planted on corner exit under power in Autocross racing or in performance driving, and it will improve the transient handling of the car (think of a slalom, same thing.)
Contrary to popular literature published by online vendors, the Miata doesn’t need a larger rear swaybar than stock to maintain a good handling balance.

5: Stock shock absorbers only last 40,000 miles. Replace these with a good quality aftermarket replacement shock. I recommend (in order) for stock application:
  1. Tokico Illumina
  2. Koni Sport
  3. KYB AGX
  4. Bilstein HD