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Ground Control Coilover Installation

Last updated 11/19/2001


I have OEM springs and KYB AGX shocks that were installed about two years ago in '99 when they first came out. For the last few months I've been noticing that my car's ride was a bit more harsh and jarring than my wife's '92 Miata, which also has the same suspension setup.

The ride height on my car has noticeably gotten lower over the years - I think my springs may have sagged close to an inch over what it originally was when the car was bought new. With a full tank of gas, the ride height (from the bottom of the fender to the center of the wheel) of my car is: front left: 13", front right: 13 3/8", rear left: 12 5/8", and rear right: 12 7/8". My wife's car rides significantly higher, perhaps 3/4" higher.

After reading Jyri's Virkki's excellent bump stop info page, I became convinced that ride height and bump stops play an important role in how well the car rides. On a Miata, bump stops are not just a rubber element that prevents the shock from jamming into the car body. But it's an active suspension element providing a secondary spring action.

My goal for the spring change was to get a more pleasant, less jarring ride. Also, since I occassionally do track events, I wanted to get a firmer ride with less body roll. The Ground Control coilover springs for the KYB AGX seemed like an ideal solution. It gives the ability to raise or lower the ride height, and it comes with stiffer springs - just right for that track day. My plan is currently to get the car back to stock height: about 13" in front, and 13 1/2" in the back.


I did a little research into the Ground Control coilovers and here's some of the threads and articles which I ended up reading that gave me some background information.

Articles from the Miata power list


Threads from the Miataforum list


Other people's Ground Control coilover pictures (M1 cars)


Rear shock install

I started by doing only the rear shocks on a Saturday, and planned to do the front shocks the following day. This way, I wouldn't be feel so rushed for time in trying to get all 4 shocks replaced by the end of the day and I'd be less tired. Importantly, it would give me a chance test drive the car, and see if there were new noises from the suspension - something that would be easier to isolate since I only replaced the two rear shocks.

Click on any of the preview pictures below to view a larger image and description.

Front shock install

Here's pictures of the front shock installation, which I did on the next day, Sunday.

Click on any of the preview pictures below to view a larger image and description.

Redoing bump stop trimming

I got an email from Jay Evans who pointed out I may have left a part the bump stop unproperly untrimmed. After studying it, I agreed, and spent a few hours taking all the shocks out again, and properly trimming the bump stops. I should have done this the first time around, but better late than never.

Click on any of the preview pictures below to view a larger image and description.

After the install


After taking a test drive, I found the current setup to ride a bit better than my old setup - this was surprising since the spring rate on the new springs are a lot higher. I haven't played with the shock setting yet - I just left them at 3 all around, same as when I had stock springs.

On a twisty roads, the car felt very solid, with no detectable body roll. On normal street driving, bumps, potholes or expansion joints on the freeway produce a sharper impact than my old stock springs, which is what i would expect with such stiff springs. But the ride quality over all is a little better.

I'm sure the ride quality will get better when I raise the car up more. When I was installing the shocks, I set the spring perches to a height that made the spring installatiion easy - ie, I didn't end up using a spring compressor when putting the Eibach springs in. I used 10 turns from the bottom on the front, and 8 turns from the bottom on the rears. This resulted in the following ride height:
front left: 12 5/16", front right: 12 9/16"
rear left: 12 3/4", rear right: 12 3/4"

The new ride height is in the front was lowerthan what I started with, and roughly the same height as the rear. The next change will be to raise both fronts and rears so the ride heights are 13" front and 13 1/2" rear. This should improve the ride even more.


Yesterday evening, I turned the spring perches to raise the car slightly. The fronts springs were turned 2 turns (from 10 to 12 turns from the bottom of the threaded sleeve). The rear springs were turned 3 turns (from 8 to 11 turns from the bottom).

This resulted in the following ride height:
front left: 12 9/16" (+ 4/16"), front right: 12 7/8" (+ 5/16")
rear left: 13 3/16" (+ 7/16"), rear right 13 1/16" (+5/16")

I found out that the spring perches can't just be turned by hand easily without doing other things - the spring was pushing against them too hard. On the >s, I could have disconnected the sway bar from the end link, but chose to use a jack to pry the a-arms away from the body, relieving the spring tension and allow the spring perch to turn up. On the front, I had to disconnect the sway bar from the end link, and this allowed me to push down on the a-arm by hand, and gave me enough free play in the spring to turn the perch up.

The small increase in ride height last night made a noticeable, more mellow ride than what I had with the initial coilover setting. Bumps and potholes became less jarring, but the ride is still taut and crisp as before. The feeling on my normal commute route on street and freeways is about what it was when I had the stock springs on. Execept there is an extra stiffness in the springs that you can notice, specially when going over a freeway when going over expansion joints or areas of patched asphalt. The ride is still very tolerable for a daily commuter, which is what I use my car for. But I suspect if I had chosen a higher spring rate, the stiffness would grow tiring for me. It's definitely not what I'd call a plush ride. Yet I wouldn't hesitate using my car for another lap of the country.

As far as the benefits, it's hard not to notice the rock steady composure on triwsy turns. You frequently hear the expression, "rides like a slot car", and with this setup, that's not far from the truth. The steadiness through a fast turn certainly gives a lot of confidence, and it feels like a cat pouncing through quick transitions.


Today, I pulled out all the shocks and properly trimmed the bump stops (see above).

When I was reinstalling the shocks, I wanted to get closer to the 13" front and 13.5" rear ride height that I originally wanted. I set the front spring perch to 14 turns from the bottom. The rear spring perch was sturned 16 turns from the bottom.

This resulted in the following ride height (the numbers in parenthesis are deltas from the previous measurement):
front left: 13" (+ 7/16"), front right: 13 1/4" (+ 3/8")
rear left: 13 5/16" (+ 2/16"), rear right 13 1/2" (+7/16")

After a quick test drive, the ride is even less harsh than before. I'm going to keep it like this for a while, and seeing if the suspension settles over time.


An update after over a year: I've been happy with the height adjustment. It hasn't sagged in the slightest over a year. I have been adjusting the KYB/AGX shock setting regularly just to see how that changes ride quality. Surprisingly, after a lot experimentation, I've settled on 5 all around. I had been running 2 all around and thought a higher setting would be more harsh. Actually, it felt like it was slightly more comfortable at the higher setting. Still, it's not a plush ride - it's something I wouldn't feel right having my grandmother ride in (well, that and the fact she's been dead for many years). But the car is my daily driver, and I have no problems using it every day, or for very long trips.

Over the last year, I've had no problems with the coilovers or the shocks. No funny squeaks or clunking noises. Overall, I've been very, very pleased.

 Questions? Comments? Send them to me at [email protected]