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  • #16
    The bump spacers go between the bottom of the strut and the control arm...very simple to install.

    Basically all they do is allow the wheels to sit further "up" (thus lowering the car) while retaining the stock suspension geometry.

    As far as the strut brace bar....yes you can still run it....because the camber plates mount inside the strut tower....if that makes sense.

    Konig- you are right....mounting the full GC coilover kit does require modifications to the strut housing that would be pretty much permanent.
    Last edited by Ironhead; 05-30-2015, 01:15 PM.

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    • #17
      I have Bilsteins on the front with H&R race springs and until I added roll center spacers, and spacers on top of the camber plates, I just blew through all the travel over the smallest bump, like pulling into the garage. The excessively low roll center just caused all kinds of issues. I ran some awesome revalved Koni sports but they didn't have enough compression damping to offset the loss of spring rate due to the bad roll center. It was horrible because the car bottomed over everything. I mean everything, undulations in the road? Yep. Train tracks? Good god. All kinds of bad. If you are going for looks, you will be compromising a few things. Ride quality will be the first thing that goes away, you will have to jack the spring rate higher the lower you go to keep it off the bump stops. Going this route, you will need higher rebound damping rates, if you don't have custom valved dampers matched to the spring rate you are running, you will end up with a bouncy ride. (I had this issue with the Bilstein sport rears. It was making me feel sea sick.I re-installed the re-valved Koni Sports and backed the damping off till it matched the lack of rebound damping on the Bilstein fronts) With the high spring rate, I've found that the car skips around and feels nervous. That said, the H&R race rears could use with more spring rate as they squat under acceleration. The lack of damper travel between Konis and Bilsteins is also an issue. The fact that the Bilsteins are a little taller than the Konis makes all the difference in the world. I'd love to run my set of Konis up front again, but the lack of travel and lack of compression damping is just a bad combination. The bilsteins have the travel, and the compression damping, but the rebound damping is lacking even for the H&R race springs, any more spring rate they are totally useless.
      Yes, the DTM cars were crazy low, but their suspension geometries and attachment points were different. It would be amazing if someone would make a set of front springs (that work on stock struts) that are about 450 lb, and rears that are in the 575 range. (Yes I know the rears could be converted to running the adjustable springs, I might go that route.) Bottom line, by design, lowering the car from stock really messes up the suspension geometry, but it needs more spring rate that what the stock rates are. Its never going to be american car/land yacht soft, but its easy to make it feel too hard, yet too soft to stay off the bump stops. Pretty much the front end is a disaster. Why didn't they run A arms rather than the disaster of Mac struts? At least that way they wouldn't lose camber as the suspension compresses. Coilovers can make the car lower, but you can't raise it higher than the dampers extend. It sounds like you want to go low, but just remember that the lower you go, the less travel you will have, the more likely it will bottom out, and the more stiff you will have to make the springs to offset all the above issues, topped off by needing custom dampers to control the high spring rate.

      Will
      '69 Datsun 2000 Roadster vintage race car (Street driven on a regular basis :taz
      '59 Alfa Romeo 101 Sprint (HUGE project :uhoh
      '88 M3

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      • #18
        RAD2LTR speaks the truth.

        We all want our cars to look like DTM cars, but the strongest advice I could give would be to refrain from significant lowering. I would not go lower than about 1" from stock ride height. If you do I think you will find that you have a car that is worthless for pretty much everything besides "posing".

        When I first got the GC suspension I figured my car was mostly a track car, so I might as well go really low. So I lowered everything, which with the tires I was running at that time gave me roughly 2.5" lower than stock. I know that doesn't sound like a ton, but it made the car into a horror show. Not only did the car bottom/scrape on EVERYTHING (including a nearly invisible road heave that did a lot of damage to my exhaust system), it also transformed into an ill handling bump steering POS that ruined the confidence inspiring handling the car was built with.

        Keep in mind these were fairly low cars with marginal ground clearance as they came from the factory, if you go much further you will wind up with nothing more than a trailer queen good only for car shows.

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        • #19
          The main reason I retained stock ride height was exactly as RAD2LTR states, not screwing with the roll centre and being able to drive over speed humps. These cares handle great as stock, probably the best trait the car possesses, why do we think we can screw with that. We can improve grip by lowering the CoG and increasing the roll stiffness and, but three comes a point where the gains from lowering of the CoG are cancelled out by the change in roll centre. Increasing roll stiffness is achieved by anti sway bars and stiffer springs, but we need to be careful that the increase in spring rates from to rear remain proportional.

          I had Bilsteins with H&R Sport springs Pt No 29664-1. It was dreadful! Under steer and lifting inside front wheel in track, excessive squat under acceleration, and even lifting inside front wheel on track. To top it all, it was really harsh on the road!

          I had the springs tested. The fronts are progressive 110lb/in-205 lb/in rising rate, hitting 205 at 5in compression. The installed length was 5.3in compression, so 205lb/in when installed. The rears are 259lb/in linear.

          If we compare those rates to the stock rates of 100lb/in front and 300lb/in rear. So an a set of springs that are supposed to improve our cars behaviour are in fact 2x the stiffness at the front and softer on the rear. It would seem that if we are increasing spring rates they need to be 3x as stiff at the rear that the front in order to maintain the similar proportion of roll stiffness front to rear.


          Went for a 150lb/in front and 430lb/in rear, which may seem excessively stiff at the rear for such a soft front spring. The car rides great, staying flat over high speed compressions, and the under steer and wheel lifting has been eradicated.

          As it turns out, the H&R 29664-1 springs are also the same spring as H&R sells for the 325i, which has a much heavier engine in the front. Go figure!
          Sport Evo No.47

          My Sport Evo Restoration

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          • #20
            The stock spring on the US model 31331130043 is $91.56 at my local dealer. The strut listed is 31322225397 ($139.52). On real OEM there are two additional springs listed for the Euro model: 31332226791 - M Sport E3 ($88.82) and 31331130046 - vehicles with AC ($91.56). Are both of these sport MTechnic options? Does anyone have this set-up? Does it drop the car a little but keep the original feel of the ride?

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            • #21
              ...The lack of damper travel between Konis and Bilsteins is also an issue. The fact that the Bilsteins are a little taller than the Konis makes all the difference in the world. I'd love to run my set of Konis up front again, but the lack of travel and lack of compression damping is just a bad combination. The bilsteins have the travel, and the compression damping, but the rebound damping is lacking even for the H&R race springs, any more spring rate they are totally useless.
              ...
              Will
              Not doubting your statement but merely pointing out some general info on mono and twin tube shock absorbers before someone thinks it's a general rule valid for any comparison between bisltein and koni shock absorbers.
              The body of a bilstein monotube houses the gas charge and the separator piston and must therefore be longer than a twin tube shock absorber (like Koni) for a given travel.
              The perceived greater compression damping is probably the internal bump stop being compressed.
              Koni offers shocks for the E30 that are limited in their travel to make them suitable for shorter lowering springs in order to maintain pretension in the spring at full droop. They achieve this by putting a spacer around the piston rod between the piston and seal/cap without needing to use a shorter housing and piston rod.
              As such one can't really tell which shock has a longer stroke by just looking at them.

              To the OP: you never replied to what rate your front springs have. You mentioned Motorsport springs, do you mean stock M3 springs by that or the genuine race item?
              My guess too is that you are riding on the bump stops caused by the shorter lowering springs.
              Do a Google on shortening bump stops inside bilstein dampers to see what's involved.

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              • #22
                The Sport Evo spring is 10mm lower, to allow the tyre to arch gap to remain the same with the 10mm larger arch cut outs of the SE front fenders.

                There are also different springs for AC non AC cars.

                I believe the spring rate is broadly the same at 100lb/in.
                Sport Evo No.47

                My Sport Evo Restoration

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                • #23
                  Originally posted by Grinder View Post
                  The stock spring on the US model 31331130043 is $91.56 at my local dealer. The strut listed is 31322225397 ($139.52). On real OEM there are two additional springs listed for the Euro model: 31332226791 - M Sport E3 ($88.82) and 31331130046 - vehicles with AC ($91.56). Are both of these sport MTechnic options? Does anyone have this set-up? Does it drop the car a little but keep the original feel of the ride?
                  US vehicles had AC standard and the weight of that is probably accounted for in the front spring (both ride height and stiffness). Euro cars had AC as an option hence the separately listed PN. Sport evo spring lowers ride height a little to make up for the larger fender gap the Sportevos would otherwise have had due to the bigger cut outs in the front wing.

                  Don't know why US spring and euro AC spring have different PNs perhaps because the US vehicles were better specced from the factory (sun roof).

                  The 130043 and 130046 were also used on other E30's (4cyl.) so probably available cheaply second hand

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                  • #24
                    Steve beat me to it, didn't mean to repeat almost the same but his reply wasnt there yet when I posted

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                    • #25
                      Originally posted by RAD2LTR View Post
                      I have Bilsteins on the front with H&R race springs and until I added roll center spacers, and spacers on top of the camber plates, I just blew through all the travel over the smallest bump, like pulling into the garage. The excessively low roll center just caused all kinds of issues.
                      Will
                      Roll center spacers have nothing to do with ride height or ground clearance... not sure if you were trying to say that or not. But to be clear, the roll center spacer goes below the hub and thus has nothing to do with the "stack height" of the spring, shock, and camber plate. It simply lowers the outboard mounting mount of the control arm and tie rod to compensate for the lower inboard mounting point you get with lower springs. Ideally you would want the thickness of the roll center spacer to match the drop in ride height. I wasn't able to do that because I have 16" wheels so I had to shave it down.

                      Regarding the original issue of overly stiff ride, I have noticed that about Bilsteins in multiple cars. I had them in an e39 and that ride felt harsher than my M3 with the GC Koni setup. Bilstein uses a traditional German philosophy of high bump damping to make a car corner well. The problem is that 1, it creates a harsh ride, and 2, in quick transitions it jacks the car up.
                      Another way to improve handling is to focus on rebound damping, this is what Koni does. It controls extraneous wheel movement just as well, but with the added benefit of a smoother ride and the car "settling down" in quick transitions instead of jacking up. This is the same suspension philosophy that Dinan uses to make their suspensions handle better than stock but also ride smoother.

                      As far as travel, get Ground Control's shortened strut housing and you won't have any problems.
                      "It is needless to say that self-propelling vehicles, like other machines, will never do as much for one who does not understand them as for one who does."

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                      • RAD2LTR
                        RAD2LTR commented
                        Editing a comment
                        Yes roll center spacer DO have an effect on ride height. The distance between the top of the camber plate and the control arm is what controls ride height and ground clearance. If you have one that measures (call it) 30 inches and another that measures 28 inches point to point, the 28 inch one will have a lower ride height (not the actual distance, just using the numbers for example). Its a set distance. If you need X distance from the strut mounting point to the control arm, raising or lowering that number will either raise or lower the front of the car. If you have one assembly that is 30 inches, it will cause the control arm to sit at X degrees to the ground. If you have one that is 28 inches long, the control arm will slope upward toward the wheel at Y degrees to the ground. The goal is to have the control arm sloping just slightly upward toward the oil pan/inside of the car. That will ensure your roll center is above ground. Yes, lowering the CoG is a good idea, but not below the point where the roll center does below ground level. Once RC goes below ground level, things go to hell very quickly.

                        Will

                    • #26
                      Thanks for the info. I am also running 16" wheels (type 5 from an e34 5 series). I'll wait th hear from Koenig on he's inquiry to GC.

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                      • #27
                        Will, I still disagree. What effects ride height is the distance between the wheel hub and the top of the strut. That is the ground point of the system. The roll center spacer is below that point thus has no effect on ride height. If the strut tube would shoot to the ground below the spindle it would have no effect on ride height. Picture unbolting those 4 steering knuckle bolts to remove the roll center spacer while the car is on the ground. What would happen? Nothing (assuming you didn't give it a push to the side). I could be wrong but I'm pretty convinced in my head.
                        I agree with all your points about the effect of the roll center and lowering it too much. You want to minimize "roll couple/moment" and when you lower a car, that gets larger. Hopefully your springs counter it, or you are able to raise the roll center.
                        "It is needless to say that self-propelling vehicles, like other machines, will never do as much for one who does not understand them as for one who does."

                        Comment


                        • RAD2LTR
                          RAD2LTR commented
                          Editing a comment
                          Well, after I added the 13mm spacers on my car, the splitter went from not clearing parking curbs to clearing them. I made no other change. Now I can pull into a parking spot and the splitter just clears the top rather than hitting. Either way, the length of the strut assembly increases by adding them (effectively). The angle of the control arm has changed relative to the ground, if its level with the ground, the car will sit lower, if it slopes outward toward the wheel, the ride height will rise because the geometry has changed (or drop if the strut length gets shorter because the control arm will now slope inward toward the oil pan) The height of the wheel stays the same, but the body will rise or fall based on the length of the strut since the control arm length does not change, it just pivots either up or down.

                          Will

                      • #28
                        Grinder , here is the response I received from GC this morning. My question first:

                        I'm looking for a sport-street suspension. While the full coilover suspension (SKU 2020.76) is appealing I want to keep everything reversible, so modifying the strut housings is not an attractive option. Is the coilover kit (2020.71) a good fit for my application? I see that there is ride height adjustment for the rear, is there any for the front? How much of a drop should I expect? Will my application require camber plates to achieve correct alignment?


                        Response:


                        Thank you for contacting us. The suspension kits that you referenced both have front and rear ride height adjustment. Kit #2020.76 is able to be installed into your stock strut housings. Shortening your strut housings is optional. When installed into standard length housings, both kits have the ability to lower up to -2.2". Our camber plates are designed to add negative camber, unfortunately if you need to add positive camber our plates will not work. Please feel free to contact me if you have any additional questions.


                        For reference, this is 2020.71:



                        and 2020.76:



                        Two questions I have:

                        1. Did he mis-type in his response, and mean to say 2020.71 instead of 2020.76?

                        2. Does 2020.71 actually offer front ride height adjustment?
                        1988 Lachs - sold
                        1988 DS - sold
                        Bay Area M3 FB group

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                        • #29
                          I'm with AlpineRunner, the RCS doesn't effect ride height. As he said, it lowers the control arm connecting point, increasing the angle of the arm. It doesn't add to "stack height" as the spacer is below the hub. The distance between ground and hub is fixed and controlled by your wheel and tire combo.

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                          • RAD2LTR
                            RAD2LTR commented
                            Editing a comment
                            Ok, based on this, we are talking about two different ride heights. I'm talking about body height, body height will change with an RCS. Think of it as a triangle, the bottom is the A arm, and it can pivot. Assume we are looking at the left side of the car head on. I'll say the right point of the triangle is the body, the two points being the inner pivot (lets call it "A"), and the top being the strut mount in the body (call that "B"). The outer end of the control arm on the bottom is "C" Now, the left side of the triangle is the strut. If you shorten that arm, while leaving points A and B fixed (since they are the body), C will have to move upward for it to attach to the strut. Assuming this takes place on both sides, the ride height of the body will be lowered because the distance between B and C has been shortened, and the distance between C and A is fixed. Obviously, going the other way, making the left side of the triangle longer, the base of the triangle will drop because the distance between B and C is now longer. Since the wheels keep everything off the ground, the longer arm between B and C now cause the control arm to slope upward toward point A. Point C is now lower than point A, so the body must rise since points A and B are fixed. Anything added between B and C will raise the ride height of the car. Adding taller wheels/tires will also, but lets not worry about that since it makes no change to the geometry of the points A,B, and C. The distance between B and C dictate both roll center and ride height. The RCS still sits above the lower control arm and above the pivot there. The pivot point at A doesn't matter, it just allows things not to break since the distance between B and C is variable (the strut) Anything that mounts between B and C will affect ride height and roll center because that is the one side of the triangle that changes. A and C are a single piece that does not change distance, A and B are the same, they do not change either. Only the distance between B and C changes therefore camber/caster plate stack height, spring height, spring hat and rubber spacer height, and RCS all affect ride height. This is what I ran into with my car. I changed from the stock strut mounts to camber/caster plates that had 1.5" less stack height, and went to struts (Konis) that were again, shorter than the Bilsteins, (so even topped out, they were shorter than the bilsteins under load. When they were loaded, the car dropped more) and I added H&R race springs that again were shorter than what they replaced. The next thing I know, the car is bottoming out the suspension over the smallest imperfection, even though the spring rate is much higher and its so low that I ripped the splitter off driving through a small puddle. The only part of the equation that changed was the distance between B and C.

                            So, what did I do to fix it? I started with spacers that fit on top of the camber plates (had to weld longer mounting studs into the plates to make them work) That effectively made the stack height the same as the stock mounts. I found a set of Bilstein sports that were longer than the Konis, that also gave me a little compression damping (its harder to compress the bilsteins than it is the Konis, even with them set full hard) This again lengthened the distance between B and C forcing C to drop from above A to equal to A under load. I then added the 13mm RCS again making the distance between B and C longer, dropping C relative to A. Now, the control arm between A and C slopes downward toward point C thereby raising point A relative to the ground. This is how RCS spacers work. They make the distance between B and C longer there by raising the car and the roll center.

                            This is why cranking the preload on a set of coilovers to the moon fails to raise the car. All you are doing is compressing the spring because the distance between B and C can't become longer if the strut is already topped out. Its as long as you can get it. Yes, you can lower the car by screwing the adjuster down because the strut will simply compress in its travel since the adjuster has been moved down the body. Gravity has shortened the distance between B and C because the spring just sits lower on the housing. B is still a fixed point. It still weighs X pounds. All you have done is lessened the amount of available suspension travel because the strut is already sitting partly compressed, and raised C relative to point A.

                            Does this make sense?

                            Will

                        • #30
                          I spoke with Ground Control today trying to understand which of their offerings best suits my application. I am comparing their Street Complete Coilover Kit, PN 2020.71 (http://www.ground-control-store.com/...ion.php/II=912) to their Complete Coilover Suspension, PN 2020.76 (http://www.ground-control-store.com/...ion.php/II=754)

                          As mentioned in an earlier post, I'm looking for slight lowering (will be going to 17s) and a sporty street ride. I am hesitant to modify the stock strut housings, because I don't like doing anything irreversible to my cars. I narrowed it down to three options:

                          1. Street suspension, no modification to housings
                          2. Complete suspension, no modification to housings
                          3. Complete suspension, shortened housings

                          I'm looking for advice on this from persons with experience with some/any of these kits. For street application, is it worth stepping up to custom-valved Konis? Is bottoming out a legitimate concern if I do not shorten the strut housings? Are camber plates beneficial on the street? Should I just suck it up and modify the strut housings?

                          Much appreciated...
                          1988 Lachs - sold
                          1988 DS - sold
                          Bay Area M3 FB group

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