Author: William Howell
The middle picture shows the difference in the shaft length on the rear dampers, and the far right picture shows the difference in shaft length of the front dampers. When dropping the ride height of a car, shorter shafts are desirable so that the spring does not lose contact with either spring perch.
The big advantage of the Ground Control setup, other than adjustable ride height, is that you can select the spring rates that you want to use. Just be aware that some dampers can be overpowered by springs that are too stiff!! The Ground Control kit includes four threaded bodies with adjustable spring perches, four urethane spring cap adapters, and four Eibach ERS springs (with pre-selected spring rates). I initially chose a 375 lb/in springs for the front at 450 lb/in springs for the rear. I have since changed the spring rates, and I am now using 550 lb/in springs in the front and 450 lb/in springs in the rear. I have also had my Konis revalved and shortened. Note that Ground Control does NOT recommend that you put stiffer springs on the rear of the Prelude. Because the rear of the Prelude is so much lighter than the front, they will usually recommend a spring that is softer than what you choose for the front. The reason for using a stiffer spring in the rear is to induce more oversteer, which is desirable for autocrossing. The harshness of the initial setup could be attributed to my original Konis. I bought them used and they were valved much stiffer than my current Konis. I don't know the specifications to which they were revalved to, but they were definitely stiffer than my Konis now. I replaced them after accidentally bottoming out one of the front dampers (DO NOT forget to install bump stops!).
Here are some pictures of the final setup:
If you notice, I do not have any dust boots on the Konis. After talking with many people that use Konis, I decided not to use dust boots since I have not heard of any problems with the Konis leaking as a result (besides, I could not find any dust boots that fit).
The adjustable spring perches are a new design by Ground Control. Their original design used set screws that applied pressure directly to the threaded body. There is an obvious problem with that design. The set screws will damage the threads on the threaded body and the spring perch could move around. Their new design, however, is much improved. Now the spring perch is more or less a clamp. When you loosen the clamping bolt, the perch expands a little, allowing you to turn the perch to adjust ride height (in many cases by hand). When you tighten the clamping bolt the perch clamps up against the threaded body so that it cannot turn. This way, the threads on the threaded body are not damaged. Another nice touch is that the spring perches and threaded bodies are made of aluminum. Very light indeed. Here is a picture of the new spring perches and threaded bodies.
Notice the cut in the perch, and the clamping bolt to the right of the cut. Here are some pictures comparing a stock front damper with Eibach Pro-Kit springs and the front Koni/Ground Control combination:
In the picture on the right, the spring on the left is an Eibach front Pro-Kit spring and on the spring on the right is an Eibach ERS spring.
The Ground Control coilover kit requires you to cut the dust boot and use it to hold the urethane spring isolator in place. For the dust boot to fit on the Koni shafts, you have to enlarge the hole to 12mm. A dremel tool comes in very handy to modify the dust boot to fit, or a pipe cutter that can handle 2 1/2 OD pipe.
The Konis fit like stock, and no modifications were needed to install them, besides the bump stops. The shaft on the Konis is 12mm vs. 10mm stock shafts, so you have to replace the steel shaft bushing (not the rubber ones) in the spring cap. If you put a little lithium grease on the new steel bushing, it will fit inside of the rubber bushings very easily. Koni supplies all new steel bushings, washers, and locknuts for the upper spring caps. The stock hardware is used for the lower damper mounts. Be careful when you install the front Konis. There is a small indention in the bottom of the damper body. This indention NEEDS to face inward. The indention provides clearance for the fork bolt that holds the fork to the lower damper body. If the fork bolt does not go in smoothly, DO NOT force it. Turn the damper body a little and try again. Also, try moving the damper up and down to get the indention in the right position.
I have a few tips for those of you who are thinking of using this combination. First of all, USE BUMP STOPS. I learned the hard way. I bottomed out one of the front struts and it cratered the damping mechanism. Instead of getting the damaged strut repaired I ordered a complete new set. On the front spring cap, use the stock isolator with the Ground Control isolator installed inside of the stock one. It will not stay in by itself, but when you cut the dust boot and install it with the Ground Control isolator it will stay in. You can barely see the cut dust boot in some of the pictures above. You can also use the stock bump stops. I just cut off the top section of the bump stop (the fattest part). Ground Control says to cut the bump stop in half, but I think that you will get some tire rub on the front fenders with that much bump rubber gone. I haven't had any problems with rubbing with these bump stops. On the rear, use the Ground Control isolator WITHOUT the stock isolator. It looks like it will not stay in place, but the cut dust boot will hold it.
For the street, I have the ride height set at about a 1 1/4" - 1 1/2" drop. I am considering raising it up just a bit because I have hit the tow hook on a few occasions. Other than that, I haven't had any problems with ground clearance. The Prelude's main problem when you drop the car is the lack of suspension travel. If you drop the car more than 2" you only have about 1/2" - 1" of travel left. It looks like the tires will rub on the front inner fender before the shock bottoms, but you can get the shock to bottom on the front. The rear looks like you can get plenty of travel out of them. I have not hit the bump stops on the rear, but I am pretty sure that I have hit the fronts a couple of times.
The car definitely rides stiffer, but with the Konis, the ride is not unbearable. If I crank the Konis up to 1 3/4 turns, then the ride turns quite stiff, but overall, with some careful tuning of the Konis, ride quality is not diminished. The Konis also completely eliminate that annoying bouciness that you get with some aftermarket springs when used with stock dampers.
Performance Impressions of Revalved and Shortened Konis
On the street this combination is definitely rough. It is on the edge of streetable and WAY TOO DAMN ROUGH. It really depends on how much your back is willing to put up with! On the track, however, this setup struts its stuff. The car handles like a go-cart. Body roll is almost nil, which is surprising considering I went back to using the stock front swaybar. Squat under acceleration is nonexistent, but dive under braking is present, although not as bad as stock. Where this system has an advantage is transitional response. The car transitions almost perfectly (in my opinion at least), and slaloms and offsets are much more fun! As one of our autocrossers put it; the car now handles like a FF car should. Keep in mind, the dampers and springs were only one part of the suspension upgrade. I also changed my Suspension Techniques sway bars to a Neuspeed bar in the rear and the stock bar up front. I also changed the stock rubber suspension bushings over to Energy Suspension polyurethane bushings.
For comments or questions, e-mail me.
This page last updated 4/3/01.