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    Cobra's Custom Shock Project

    I have been meaning to share this project with you fellow enthusiasts for a while, but didn't want to share anything before I could get some miles in and give a proper review of the setup.

    After about a year of research, fabrication, and testing, I’ve finally finished a custom shock setup for my M3! This was quite a learning process to say the least. I am lucky enough to have access to some pretty neat tools, parts, and smart people in the suspension industry, which helped making this one-off setup possible.

    Project goals
    Overall, I wanted to improve the comfort, handling, and capacity to drive rough roads without bottoming out. It would also be nice to adjust the compression and rebound without removing the shocks or wheels, since that can be pretty cumbersome (looking at you, Koni rears).

    Why not just buy something pre-built? Part of it was having access to the components, but I also wanted to turn it into a learning opportunity. To not only end up with a nice setup, but know how to get there and how to continually improve it!

    For reference, my car previously had Dinan springs (175lb/in front, 475lb/in rear) with Koni shocks, and is stock other than some 245/275 tires on 18’s.

    Rear shocks
    For the rear, I used 2.0" monotube aluminum piggyback dampers with base valves. This reservoir positioning is convenient because I could avoid any modifications like drilling into the trunk or using any long hoses. The only thing is I had to convert the upper mount from the stock bushing to a clevis which required machining a mount.


    The shock in place



    The rebound adjuster


    The Dinan springs (left) compared to Eibach's Extreme Travel 650lb springs (right).


    Front struts
    The fronts were a lot trickier since it's a strut and therefore a structural component that both pivots and rotates. I ended up using 2.0” monotube steel struts with a detachable piggyback. This was required so that the reservoir can be attached after installing the strut body into the knuckle. I did not have access to inverted strut body components at the time, so these are using a conventional architecture with a large shaft and oil flow through the bottom.


    Initial install with 300lb/in springs.



    After switching to 375lb/in springs.


    Rebound adjuster


    Setup
    I went through a number of spring and damper iterations. Honestly, the first thing I tried was damn good and a huge improvement over stock. But there was still room for improvement. It was a bit soft when pushing hard, and the balance was a little off from a damping perspective. I experimented with the "flat ride" spring rates with and without rear swaybar, but it wasn't quite right for my preferences.

    Halfway through, I hooked up a data acquisition system to monitor shock position and speeds to help speed up the process and know where in the travel it was operating. It is pretty eye opening, and shows that what you feel might not be what’s happening at all!

    I finally settled on 375/650 spring rates, which puts it right around 2Hz front and rear. Ride height is 14” all around. Bump travel is maximized for my wheel/tire setup, and droop travel is only 1” less than stock. The dampers are matched accordingly and are pressure balanced at all speeds. I would say the tune is something between a street and track setup – firm but still compliant enough to handle anything from a bumpy mountain road to smooth high speed curves.

    Driving impressions
    It’s pretty amazing how much shocks can change a car. I’d say it’s the first or second thing anyone should do when modding their vehicle, right up there with wheels & tires. It completely changed the character of it!

    The handling is so much sharper, and it can soak up anything I throw at it from bumps to pot holes to hard cornering. Seems like the faster it goes, the more planted and at home it feels. If I had to pick an area to improve, it would be that 2Hz is a little firm for city driving, as it tends to follow the undulations of the road. The 300/475 rates were definitely more compliant and would be a solid choice for a purely street driven car as well.

    The next step will be making them electronically adjustable, which adds a ton of complexity but should be doable. That would be mostly for the learning, as I think these definitely do the job.

    Anyway… I hope you guys enjoyed seeing something different! Also I should mention... as you can see I am using FOX shock components hence the sweet stickers, but these are not an official product of theirs.


    Here are some really great resources I found during my research if anyone is interested:


    Building a fast car? Get $400 OFF the VIP package and never pay for another course, EVER: https://hpcdmy.co/vipy19Learn to set your suspension up the RIGHT ...


    Autocross to Win, a technical discussion of preparing winning autocross cars.

    Last edited by cobra; 08-22-2022, 08:27 PM.

    #2
    Pretty darn impressive...

    Comment


      #3
      That's awesome. Many questions:

      Were you seeing travel issues in the rear with the Dinan/Konis?

      How much bump travel do you have now at 14"?

      It looks like you have essentially no rubber isolation in the springs or dampers. Do you think that contributes much in the way of NVH?

      Are the strut mounts modified or just custom spring perches?
      2003 Imola Red M3 w/ SMG

      Comment


        #4
        Cobra,

        I was not able to clear are these
        double individually adjustable? or,

        Single adjustable via the top knob?

        Thanks,
        Anri
        https://www.instagram.com/euroclassicmotors/.

        www.euroclassicmotors.com

        Comment


          #5
          Originally posted by K-Dawg View Post
          That's awesome. Many questions:

          Were you seeing travel issues in the rear with the Dinan/Konis?

          How much bump travel do you have now at 14"?

          It looks like you have essentially no rubber isolation in the springs or dampers. Do you think that contributes much in the way of NVH?

          Are the strut mounts modified or just custom spring perches?
          -No travel issues in the rear with the Dinan/Konis. In the front, however, the shocks were basically touching the bump stops at ride height, so I wanted to improve that.
          -I will have to check my drawing, but it's right about 2.75 inches of bump metal-to-metal in the front and rear. I will update the thread with some pictures and more accurate numbers.
          -I was definitely concerned about removing the rubber isolation. In the rear, there are sphericals top and bottom. There is more noise transmitted to the cabin, but no discernible vibration or harshness. In the front, I don't notice any differences.
          -The strut mounts are stock, with adapters to use 2.25" springs.


          Originally posted by Anri View Post
          Cobra,

          I was not able to clear are these
          double individually adjustable? or,

          Single adjustable via the top knob?

          Thanks,
          Anri
          I guess you would call them "triple adjustable", because they have Low- and High- Speed compression, and Rebound.
          Last edited by cobra; 08-23-2022, 10:22 AM.

          Comment


            #6
            What's the cost involved in this vs. buying a true rear coilover setup?
            2004 BMW ///M3 Carbon Black/Cinnamon 6MT
            2005 BMW ///M3
            Interlagos Blue/Black 6MT Dinan S3-R

            2008 BMW ///M3 Alpine White/Bamboo/6MT Track Build
            2000 BMW ///M5 Royal Red/Extended Caramel 6MT
            2004 BMW X5 Toledo Blue/Sand Beige 6MT
            2023 Toyota Supra //A91-MT CULG/Hazelnut 6MT


            Instagram

            Comment


              #7
              Cool stuff. Monotubes FTW.
              DD: /// 2011.5 Jerez/bamboo E90 M3 · DCT · Slicktop · Instagram
              /// 2004 Silvergrey M3 · Coupe · 6spd · Slicktop · zero options
              More info: https://nam3forum.com/forums/forum/m...os-supersprint

              Comment


                #8
                Originally posted by Sharocks View Post
                What's the cost involved in this vs. buying a true rear coilover setup?
                From a cost perspective this project made absolutely no sense 😂. It turned into more of a passion project than anything else. There was a lot of time spent measuring, machining, and researching...

                Regarding a true rear coilover, I was hesitant about putting all the loads through the shock mount since it wasn't designed for that, so I kept the divorced spring setup.

                Comment


                  #9
                  Wow, amazing! I wish I could feel the ride in your car. If you're ever in Socal. Lol. I met Raj and drove his car with the dialed v3s, I was so impressed with how smooth it rode. Congrats to engineering what looks like a really great setup.

                  Comment


                    #10
                    Did you measure the unsprung mass yourself or use a default value?

                    Comment


                      #11
                      Originally posted by enjoy_m3 View Post
                      Wow, amazing! I wish I could feel the ride in your car. If you're ever in Socal. Lol. I met Raj and drove his car with the dialed v3s, I was so impressed with how smooth it rode. Congrats to engineering what looks like a really great setup.
                      Nice! I characterized those KW's and thought they were pretty good, just a bit inconsistent left-to-right. They have a lot of damping range to adapt to a variety of spring rates or driving styles.

                      Originally posted by eacmen View Post
                      Did you measure the unsprung mass yourself or use a default value?
                      I just used FatCat's numbers from his spreadsheet for the unsprung masses. They seemed to be in the ballpark. Would definitely be interesting to measure them though.

                      Comment


                        #12
                        Awesome. Love this!

                        Comment


                          #13
                          Originally posted by cobra View Post
                          "triple adjustable", because they have Low- and High- Speed compression, and Rebound.
                          Cobra,

                          Nice, so it's 3-Way adjustable.

                          Fox shocks do offer a custom build so do JRZ to example.
                          Long ago I called Fox and asked for custom shocks but I
                          got a pricey quote...

                          Not sure what coin did you spent on them but its a good
                          to have 3-way adjustable.

                          Regards,
                          Anri


                          https://www.instagram.com/euroclassicmotors/.

                          www.euroclassicmotors.com

                          Comment


                            #14
                            Here is some more information about travels on the E46 in the REAR, in case anyone was wondering. My references are Koni's and KW V3's.

                            At full extension or full "droop", there are some differences in shock lengths. I tried to match the Konis since I knew they worked, but ended up making them 1.5" shorter so that the stiffer, shorter rear springs would not become loose at full extension. The KW's are shorter yet, at just 22.5" long.

                            Koni droop travel = 4.5"
                            Cobra droop travel = 3.0"
                            KW droop travel = 2.75"

                            Click image for larger version

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                            At ride height (13.75" from the center of the wheel to the fender edge), they are all pretty similar. The Koni's will touch the bump stop the earliest, and the KW's have quite a lot of travel before touching the bump stop.

                            Click image for larger version

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                            At full compression (the point at which my wheel hits the inside of the fender), the bump stops are pretty heavily compressed!!!

                            Click image for larger version

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                            What was really cool was collecting position data and seeing just how little travel gets used. I adjusted the scale so that 0 is full extension and 7.5" is the metal-to-metal travel. As you can see, at most it gets within 1 inch of full extension, but does get into the bump stops a surprising amount.
                            Click image for larger version

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                            I took lots of measurements, and CAD'ing it up really helped visualize how things will fit. So if anyone is confused and wants to send me your shock dimensions I can try to help out.
                            Attached Files

                            Comment


                              #15
                              In the FRONT it's a little different. For my reference distances I used the OEM spring perch thrust bearing, and the little ledge where the shock bottoms in the steering knuckle.


                              At full extension (for the KW), it looks like this. Which I am learning is a bit irrelevant because unless you're jumping the car it will never reach this point.
                              Click image for larger version  Name:	front extended.jpg Views:	0 Size:	54.1 KB ID:	181745

                              At a ride height of 14", take a look at the Koni relative to the bump stop. There is very little space there before it touches. In fact, with the Dinan springs, ride height in front is more like 13.75, which closes the gap and makes them rest on the bump stops at all times. Someone here made small shims to put under their Dinan springs to raise it up, which I think is a great idea!
                              Click image for larger version  Name:	front ride height.jpg Views:	0 Size:	44.2 KB ID:	181744

                              At maximum compression, things get interesting. The way I measured this was I removed the spring and only installed the shock into the knuckle. Then I raised the wheel little by little, turning the steering wheel side to side to see at which point the wheel would hit the inner fender. I didn't go full lock to lock, since I didn't think that was realistic. The point at which things crashed was at 11.5" from wheel center to fender.

                              In this case, the Koni has defied physics and has gone straight through the top out plate. The cobra shock has only a teeny tiny gap, and the KW bumper is halfway compressed. My conclusions from this is that the Koni is definitely limiting bump travel because the body is so long. I would not run those shocks on a lowered car unless you want an uncomfortable ride when hitting bumps.
                              Click image for larger version  Name:	front max compression.jpg Views:	0 Size:	65.0 KB ID:	181743

                              Lastly I looked at the data in front. I noticed the front uses less travel when cornering. I think the stiff sway bar has a lot to do with this. Of all the data I collected, it never got within 1.5" of topping out or within 3/4" of bottoming out. So again, the shock could be shorter and probably never notice it.
                              Click image for larger version  Name:	front data.jpg Views:	0 Size:	84.4 KB ID:	181746


                              Anyway this was a super fun learning experience and hope you guys enjoyed.

                              Comment

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