Tein Flex Z’s on my 8th gen

Two years ago, I installed my first set of Tein Flex Z’s on my ’98 Honda Civic. At that time, I was in the market for some coilovers that were going to be installed on my “budget” daily/track toy, and I’ll admit the price point of the Tein Flex Z’s is what first lured me in. After doing some research and reading all about them on Tein’s website, I decided to go ahead and give them a shot. You can read all about my install and review of them from two years ago by clicking the link below.

Is this the BEST civic ever?!

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Fast forward two years, and I’m again looking at trying to get into an entry-level coilover for my daily-driven 8th gen. For the 8th gen, there isn’t much out there that isn’t either a million dollars or entry-level stuff. Sure, I could have done Ground Control/Koni Yellow, but since the 8th gen has a MacPherson front, this meant that I was going to cut up the OEM shocks since the Yellows were just a cartridge and didn’t have the bracket that attaches the strut to the spindle. This isn’t necessarily a hard thing to do; it just wasn’t really a “complete” bolt-on affair. Other options were Fortune Auto coilovers, BC Racing, Stance, Skunk2, Godspeed, K-Tuned, K-Sport, and Function Form. The problem I had with all these options was that they are all Chinese-made. Even the Fortune Auto, while being hand-assembled in America, were still just made with inferior Chinese materials (apart from the valving shims and the shock oils they install). This just doesn’t instill confidence that any of these are built to stand the test of time.

Before you start going off raving about how you have Brand X, Y, or Z and you never have problems, let me explain myself. As with just about anything, ask any two people the same question and you’ll probably get different answers. For example, “person A” has “brand X” coilovers and he loves them, while “person B” has the same brand coilovers and they probably have some negative things to say about them. Let’s break this down a little more…

“Person A” is a regular on the show car scene. Doesn’t drive his car on the street other than going to a meet, or he might even trailer his car to shows. Now, of course, since he is only putting a few hundred miles on his car a year, his “Chinese coilovers” are going to “love him long time.” Since he is not really concerned with the coilovers’ performance, he thinks the car rides nicely and handles well.

Now, let’s introduce “person B.” He has the same coilovers as “person A,” but he daily drives his car and lives in a city where the streets aren’t good. Let’s say that “person B” drives the average 12,000 miles a year. He is most likely going to have blown out his “Chinese coilovers” and have negative things to say about whatever brand they are.

The whole point of this fictional story was to help you realize that just because someone on a forum, or Instagram says their coilovers are great… that doesn’t necessarily mean they are. Hell, most of the time when people post about installing new coilovers, they rave about how great the car feels, rides, and handles, but they haven’t even driven for more than a day on them. Plus, who are they really trying to convince… Us, or themselves? I love seeing when someone comments on an Instagram post of someone who just installed new coilovers… “Hey bro, how do you like those coilovers?” OP states he loves them, and they feel great backing out of his driveway… the person replies “Sick bro, thanks. I know what coils I’m going with when I finally decide to buy a Civic.”

One last thing to keep in mind is that shops can completely customize a Chinese-style coilover by doing custom valving, adding good shock oil, and slapping on some Swift, Hyperco, or Eibach springs. This can totally transform the coilover into a high-quality product, so keep that in mind when you see “cool guys” with certain brand coilovers on their track car… most of the time, they have gone through and customized them. At that point, you would be better off just buying high-end coilovers. DON’T BE FOOLED.

When I first decided to go with the Flex Z’s on my ’98 Civic, I was not only lured in by the price but also impressed that the Flex Z’s were manufactured in Japan. This helped me take comfort in the fact that these were going to last and stand up to the abuse I was going to be dishing out.

In the two years the Flex Z’s have been on my ’98 Civic, they have done everything that would be expected and more from an entry-level coilover. In 2019 alone, I did over 10 HPDE weekends with them and racked up over 15,000 miles on them, and they still work just as well as the day I installed them… No leaks, and all adjustments in damping are noticeable throughout the whole range.

Don’t worry, there is a downside to them, two of them to be exact. One, they are a monotube shock, which is not the best for performance-oriented coilovers. This can lead to excessive bubbling or foaming of the oil which can alter the characteristics of the coilover. Two, they aren’t really the most comfortable coilovers around, and the damping leaves a lot to be desired. I knew that at the low price these were offered at, of course, there was going to be some sacrificing, and for my ’98 Civic “budget build,” I was ok with sacrificing ride quality for the assurance that the coilovers would hold up to everything I was going to put them through.

Enough talk about my ’98 Civic, let’s get into the detail about the 8th gen Civic and how I ended up going with the Tein Flex Z’s. I’ll be honest, I was a bit hesitant to buy the Flex Z’s because I knew from experience the comfort level wasn’t there, and I was really trying to make the 8th gen more on the comfortable side.

If you keep up with the blog, you’ll know that after getting my RPF1’s, I wasn’t happy with how high the car sat, and it needed to be much lower to achieve the look I had envisioned in my head. Remember the “comfort goal” I had in mind for the car… Your girlfriend had to not hesitate or sigh when you said you guys were taking your car to dinner. If she hesitated or sighed, this meant that the car was too uncomfortable, bouncy, or embarrassing to ride in.

I was leaning heavily towards Fortune Auto coilovers, but the fact that they had such a long lead time to be built and shipped out, the price point was high compared to other entry-level coilovers, and they have the Swift spring upgrade option, which wasn’t that much, but I just couldn’t justify spending nearly 2k on some coilovers. Sure, the Swift springs would have made the car feel great, but the price was just too hard to justify. Then Skunk2 was running a promotion for 25% off all coilovers on their website, and I’m not going to lie, I literally had put them in my cart twice and almost completed the transaction if it wasn’t for the fact that I know personally these coilovers are very stiff and bouncy.

In the back of my mind, I kept remembering that I couldn’t sacrifice the comfort that I was aiming for. I then stumbled across an article on Moto IQ about installing Progress coilovers on one of their daily “do everything” 8th gen’s. They had lots of great things to say about the ride quality and handling of the Progress coilovers. The Progress coilovers were made in the USA and came in at an entry-level price range.

It was settled then, Progress coilovers it was going to be… or was it? After looking into the Progress coilovers more and seeing pictures of the cars that had them installed, it became apparent that these were not going to lower the car to the extent I was looking for. Even though I was excited to get the Progress coilovers, they just weren’t going to lower the car enough, and I knew in the end I wouldn’t be happy with the way it would look.

No matter what I did, I would always end up looking at the Flex Zs. They had most of what I was looking for, but the only hang-up I had was the fact that they didn’t ride that nicely. If you had the damping set very low, the ride was incredibly bouncy; then, if you cranked it up, the ride became too stiff. The combination of spring rates, valving, and the monotube design was really hindering the performance of these coilovers. Again, the fact that they were cheap and would be able to last was a very enticing offer and was making my decision even more difficult.

I stumbled across a post on a forum about someone who had nearly the same experience with Flex Z’s as I did; however, he found what seemed to be a good solution: Preload! Sure, preload might not be the correct answer and might even be more of a band-aid rather than a permanent solution, but it gave me hope that there was a way to make the Flex Z’s ride a little better.

Before I go into talking about some basic preload facts, please keep in mind that preload is a very misunderstood aspect of suspension tuning, and there are many variables/opinions as to why it’s good or bad. I’m not here to tell you that it is necessary or not; rather, I’m just here to shed a little light on what preload is and what it does to suspension. Plus, preload is a free adjustment you can make to pretty much any coilover, and it’s totally reversible, so why not give it a try and see what it does for you.

Oh boy, where do I even begin? Preload is what it sounds like… Preloading the spring tension. There should always be some sort of preload on all coilovers; otherwise, at full droop, the springs will be able to move freely. Now keep in mind that there are two types of spring rates: Linear-rate springs, which remain constant, no matter how far they’ve been compressed or how much load’s been placed on them, feature coils spaced evenly apart. Progressive-rate springs have varying rates that increase alongside load and are made up of unevenly spaced coils. For the sake of our discussion, it’s safe to say that all major brand out-of-the-box coilovers come with a linear spring rate, while most lowering springs and most OEM springs will have a progressive rate.

A progressive rate spring allows the suspension to soak up all sorts of different terrain while remaining comfortable for the driver; therefore, pretty much all OEM springs are of a progressive rate type. They can be set to have a few coils be stiff to allow the car to handle decently, and then have some that are softer to help cushion some of the harshness of any road.

Then there is a linear rate spring; this type will have the same spring rate no matter what forces are applied to it. Therefore, most coilovers are on the stiff side because if the spring rate is too low, the suspension will be too soft. Please keep in mind that this is a very rudimentary explanation, and I’m only explaining it this way to help you better understand the differences. There are many other variables and almost infinite adjustability when it comes to setting up a coilover.

Sure, it is possible to have a soft linear spring if you have the valving (compression and rebound) set up to work with a soft rate, and on the flip side, if you run a stiff linear rate, then you can also set up the valving to work with that too. Therefore, with most aftermarket coilovers, it is nearly impossible to have your suspension set up to be both comfortable for daily driving and perform well at the track.

Before this post spirals out of control down the rabbit hole of suspension tuning theories, let’s get back on track. I’m only here to briefly discuss preload and what effects it had on my Tein Flex Z’s.

So, let’s just say that you have a linear spring rate of 400 lb./in, what this means is that it will take 400 pounds for the spring to compress 1 inch. Now stay with me here, so say you took a person that weighed 400 lbs… have them stand on the spring and it would compress one inch. The only things that have changed about the spring are the total length of the spring and the amount of force now needed to be applied to make the spring act like a normal spring. This being because sitting alone by itself on a work bench or its “free spring length,” let’s say the spring is 8 inches in total length, then add the person (400 lbs) the spring is now a total length of 7 inches because we have used the 400-pound person to compress the spring one inch.

Preload is pre-adding the 400lbs of weight to the coilover before the weight of the car is added and further compresses the spring. Adding the 400lb of preload is done simply by turning the spring perch on the coilover until it has moved one inch from your base measurement. The proper way to set preload is to ensure the spring perch isn’t loose enough to allow the spring to jiggle and not tight enough to start to compress the spring. Usually, if you can spin the coil spring around with a slight amount of effort, this is “zero” preload. Of course, no one would ever want to add a full 400lbs of preload (well, not anyone with a daily driver) and all those numbers I just used were just random ones I made up; I was only using them for explanation purposes.

Keep this in mind. The short answer is that preload prevents the shock from moving AT ALL until you overcome the preload. So, suppose you have 400# springs and you wind in 1″ of preload. That preloads the spring with 400 pounds. At that point, it takes 400 pounds of force on the spring before it moves at all. Once you’ve reached the threshold where it starts moving, it then acts like a normal spring.

That is, of course, SPRING force, not WHEEL force. Wheel force will probably be less, depending on the geometry of your suspension.

Now that you understand a little more about spring rates and preload, let me try to explain a little more. The biggest misconception of preload is that by adding preload it will increase your spring rate… NOT TRUE, your spring rate will not rise by increasing the preload, the spring is still a 400 lb./in spring all you have done is increased the preload. Preload does not alter the spring rate. The spring does not get harder or softer via preload.

Adding preload to this spring to get more shock travel without using a harder spring.

It’s the same reason Honda used a shitload (metric measurement) of preload on the stock spring. Soft spring…but maintain shock travel in a limited space. Easy peasy.

Preload adds compression travel.

OK, are you all still with me? By adding the 400 lbs. of preload, the car’s weight has less impact on the overall length of the spring, or the Static height spring length (length of spring with the car flat on the ground) is not as impacted as it would be if there was no preload on the spring. Adding the preload will increase the compression travel and allow the shock piston to potentially be in a more central position of the shock, allowing for more even up and down stroke before hitting bump stop or bottoming out.

This will make the car feel much better since the shock piston won’t always be so near the end of its stroke. This means more oil can flow and there is a more linear shock feel instead of being so near the bottom of its stroke that it bottoms out on moderate bumps. Using preload to add compression travel will increase the amount of time the suspension has to absorb the bump and then release that energy to put the spring back into its neutral position.

Bump stops are also harder than springs. With added preload, fewer bumps will be big enough to hit the bump stop. So, the car will ride smoother. Keep in mind some companies design the bump stops to be used as a secondary shock to slow the suspension travel down and have taken this into consideration when deciding on what spring rates to choose for their coilover.

Please keep in mind there are plenty of other variables and endless opinions on preload; this is only a basic overview. If you were getting more serious, you would of course consider various factors, one big one being Motion ratio: The wheel hub and the shock move at certain RATES. Meaning that as the wheel moves up and down due to suspension compression/extension, the shock also moves. Motion ratio is the RATE at which those two components move, relative to each other.

Now we can’t just add preload and magically expect it to fix everything. No, there are a few downsides to preload, and one of the main ones is that although preload will increase compression travel by allowing the shock to be less compressed at static ride height, it will decrease the droop travel, effectively limiting the amount of travel the wheel can move downward. This can cause your car to “tripod” or have one wheel come off the ground more easily when going through a fast corner.

If you apply too much preload, you can even make it so there isn’t enough wheel droop to allow the suspension to completely cycle (of course, this is in very extreme cases). One other thing to consider is that adding preload will make it more likely for the UCA to hit the shock tower because the suspension will compress more before the shock bottoms out. You’re adding shock compression travel and shortening the overall length of the coil spring.

Ok, now that you have read all that, hopefully you have a better understanding of preload and spring rates. I made sure to carefully word what I was saying and tried not to specifically state any one way or thing is better than another because, like most car modifications, things are subjective to driving styles, chassis platforms, styles of racing, and just about anything else.

With all that being said, please take a chance at doing some beginner suspension tuning with the knowledge you have gained from the above paragraphs. Adjusting preload a few mm’s (5-10mm) isn’t going to hurt anything, and you might even end up liking those adjustments you have made. You may even want to make incremental adjustments until you start to see negative effects, then go back a few from there. The only way to truly learn is by experiencing it firsthand, so go on out to the garage and give it a try.

Let me preface by saying that I’m actually pretty happy with the ride of my Tein Flex Zs after adding some preload to them, which you will read about below as I go through my installation process of the Flex Zs on my 8th gen. Please keep in mind that the amount of preload you will want/need will vary greatly depending on coilover manufacturer, spring rates, the chassis you are installing it on, and what type of suspension the chassis uses. Please don’t just assume my measurements below will work for you, but they are a good place to start.

Below is what comes included in the box. (notice the rear coils are a progressive spring)

I’m going to set the preload before I even install them on the car since I know they won’t feel good without it. Do this by loosening the lock ring. I bet you have always wondered why coilover wrenches come with a “square hole.” Well, now you know; it’s for a 1/2-inch ratchet so you can increase leverage. I chose to also use a 1 1/2-inch tube as a breaker for reference, just so you could see your options. (I do have more than one 1/2-inch breaker bar or ratchet.)

Once you have cracked loose the lock ring you can ensure there is no preload on the spring and then make your measurements.

I measure from the flat part of the top of the spring where it sits flush against the upper perch to the lower spring perch (there is a small lip on it, just about the 7 3/4-inch mark of the tape measure)

Below you can see just how small an amount of preload I added. (I think it was 8mm of preload) The coilover at the bottom has the preload, and the one above has zero preload.

On the Teins, there is an indicator on the collar so you can count the number of full rotations. Teins use a 2mm thread, so I made four full rotations and it gave me 8mm of preload.

Now ensure that both coilovers have the same preload, tighten back down the lock rings and you’re set to install.

before coilovers

I’ll spare you the details of how to remove the old springs/struts and install the coilovers. I have already done the how-to when I installed the Swift springs. You can read the step-by-step process by clicking the link below.

How to lower an 8th gen civic

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If you didn’t want to read that, here’s a super-fast run-through… Gain access to the three bolts that secure the top of the strut to the chassis by popping the hood and removing the two plastic pieces on the windshield cowl. Unbolt the brake line and the sensor wire from the strut. Unbolt the two lower strut bolts that secure the strut to the spindle. The strut will now fall right out. To install the new coilovers, just do the same thing as removal (except I usually hand start one or two nuts on top just so the coilover can hang while I get the spindle all lined up).

Bam! all done, on 8th gens it’s pretty damn easy to install the fronts.

Now on to the back, you must move some truck interior to gain access to the upper shock mount. It’s just a few (3 if I remember correctly) and the plastic trim piece that goes along where the truck latches too. You can then gently pull back the interior and just fold it out of your way.

You need to use an Allen wrench to hold the shock shaft, so it doesn’t spin while you take the wrench and remove the nut.

Hopefully this picture will give you a better idea of what I mean about “folding” the interior panel out of the way

I didn’t cover the step-by-step process for the rear either, since I covered it when I did the swift spring install. (Click the same link above to read about the rear). The reason I showed how to access the rear shock in the trunk is because I didn’t have to do that when I installed the swifts.

The rear is relatively easy too. If you don’t want to read the link above I’ll briefly go over the process. You’ll want to unbolt where the E-brake bracket mounts to the rear arm, also remove the sensor wire. Then disconnect the bolt from the camber arm where it attaches to the spindle and remove the rear sway bar end link. Lastly, unbolt the lower shock bolt. Now you’ll be able to push down on the rear suspension and the coil will come out. The adjustable part of the rear coilover fits into the upper part of the coil mount on the chassis and the spring itself rests on the lower arm.

There are threads on the Tein rear shock; this is how you will set preload to the rear if you want. (I did not) You just want to adjust the length of the rear shock so that at full droop of the rear suspension, the coil spring still has a slight amount of tension. If you don’t, you might get some clicking, clunking, or rattling when going up driveways at an angle (or any other time the rear suspension is completely unloaded).

Below is what the car looked like without any adjusting of the coilover, camber, or the springs settled.

Believe it or not, this still wasn’t low enough for me. The unfortunate part is that because I’m running a 245 tire on a 9-inch-wide wheel with a +35 offset, the inner part of the tire rubs on the coilover lock ring/spring perch. UGHHHHH. Yes, I could have just put more positive camber on the front, but then I would have had to roll/modify the fenders, and I didn’t want to do that. I really wanted the car to remain as close to stock body as possible.

I was able to add 3mm spacers, and then I had enough clearance to lower the car more. But yes, exactly, you can’t safely run any size spacer with standard-length wheel studs. Well, you can, but I wouldn’t recommend it. You need to have at least 7 full turns of the lug nuts (before you torque them down), and with the standard-length studs, I was only able to get 5 full turns.

You know me and OEM; no ARP studs for me, especially on a car that didn’t need to have increased strength studs. Check out my solution below!

Thats right OEM studs that are 10mm longer than stock. Part number is 90113-S84-901

I wouldn’t say that you should use these over ARP studs on your high horsepower or track car. For my daily driver, though, they are perfect.

Let’s go through the process of installing the new wheel studs. On the R18 Civic, you can remove the old studs and install new ones without having to press out the wheel hub. This is because the hub on the R18 Civic is smaller than the one on an SI model. So, if you’re doing this on an SI, you will have to remove the front wheel hub. Usually, it’s best to press it out (yes, there are other methods, but I’m not going to talk about those since they usually end up damaging the bearing). As for the rear, I didn’t do any studs on the rear since I don’t need to run a spacer on the rear, but I imagine it would be easy; usually, the rears are always easier than the fronts.

You will need to start by removing the brake caliper’s two 17mm bolts and then tucking it out of the way. (Below you can see I have it hanging by a zip tie)

You’ll have to rotate the wheel so that the lug nut I’m pointing to below is always in the same position for each stud that you will hammer out. This is because there is a small groove in the hub that will allow for clearance so the stud can come out.

Now since I’m not going to reuse the old studs, I’m just hammering them out. Just one or two good smacks with a large hammer, and they will just pop out. If for some reason you want to save the studs and reuse them, just thread an old lug nut on and give it a few smacks, then unscrew the lug nut so the stud can slide out.

Below you can see the stud loosely sitting in the hub; you will be able to just reach around to the backside and grab it with your fingers — it will come right out.

To install the new studs, I would suggest getting this tool. yes, you can just use old lug nuts and washers. But this tool has a bearing built into it so it can freely spin as you tighten down a lug nut. this is good because it will prevent you from damaging the threads on the new studs.

I just used a base model lug nut i had laying around.

I lightly used an impact gun to “set” the stud. Then after they were all in, I used a breaker bar to make sure they were firmly set. If you go crazy with the impact or put too much force with the breaker bar, you can possibly snap the new stud. Remember, torque specs of wheels are only 80-95 lb./ft.

Below you can see the one new one compared to the other 4 old ones.

Rotate the hub so the stud you are going to remove is lined up with the groove on the spindle.

below you can see the two studs at the bottom are new. Again I have moved the hub so the stud i’m removing is aligned with the groove in the spindle.

Below you can see i’m using the impact to “lightly set” the stud

There you go, all the new studs are in. Just repeat the steps for the other side.

Below you can see the 3mm spacer now installed with the new studs. Now there are enough threads safely secure the wheel.

A close-up of the wheel installed. I’m not sure why I took this. Because before the spacer, you still couldn’t see the wheel studs in the lugs.

I was now able to lower the car to my liking. The only other issue I ran into was that the rear coil spring height adjuster part was maxed out low, and the car still wasn’t low enough in the rear. I ended up removing the lock ring from each side. This was enough to get the car low enough for my liking. I have over 5k miles like this and no issue without having these lock rings. As you’ll see in an upcoming blog, I take a road trip to Texas and back without any problems.

Below are some pictures of my car that I took a week ago, and this is most likely the car’s final form for quite a while. I do have a few more upgrades that I will be doing blog posts on. You just can’t see them on the car because of the way the pictures are taken (but they are there).

Also wanted to mention my alignment settings. I’m running -2.5 camber front and rear, with zero toe up front and 0.2 degrees of total rear toe. I had to slightly shave the front and rear inner lip of the fenders, nothing crazy, and the body, as you can see, still looks stock. I still have full front splash guards and only have slight rubbing of them under full lock turns (like a u-turn). Wheels are 17×9 +35 front plus three mm spacers, making the effective offset +32 up front. The rear is 17×9 +45, and I’m running 245/40 tires all around.

As always, thank you for taking the time to read my meandering thoughts. I know there is a lot of info to digest, and because I’m no expert I’m sure I didn’t explain it in the simplest way. Like old Albert says, “if you can’t explain it simply, you don’t understand it well enough.” Hopefully, you can take away something from this post and apply it to your own life, car, hobby, etc. If you have questions or want to have some conversations about what was discussed in this article, please feel free to reach out to me via Instagram @Functiontheory, Email Billy@Functiontheory.com, or simply comment on the post below.