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    E30 M-tech springs

    My E30 came with the M-tech suspension option from the factory; Bilstein HD's from the factory (yellow mono tube, BMW stamped) and associated m-tech springs.

    I had bought H&R OE sport springs and was surprised when I went to swap them that the M-tech springs were quite a bit thicker. Felt a bit weird swapping beefier springs for thinner springs

    In the near future I plan to swap back to the M-tech springs as I found the OE sports are softer and I preferred the linear feel of the original springs versus the progressive nature of the H&R's.

    That aside, I have been trying to do research on the M-tech springs, as they don't seem to come up in the ETK or places like real oem.

    The front springs are stamped "BMW 11327422RBW 46 C" and marked with 4 hot pink dots.

    The rears are marked 1132317 and are marked with 2 red dots.

    Anyone have a way to look these part numbers up?
    Attached Files
    Your resource to do-it-yourself and interesting bmw and e30 stuff: www.rtsauto.com

    Your resource to tools and tips: www.rtstools.com

    #2
    From memory the H&R front springs have 6 turns. The factory sport spring has 7. For the same spring wire diameter, the spring with 6 turns will be stiffer than 7 so the 7 turn with a slightly larger wire diameter will still be softer.

    I've read the H&R front rates are ~180 lbs/in and the factory sport are closer to ~120.

    Comment


      #3
      Thickness should play a substantial role in spring rate, and considering these are not normal sport springs (these are derived from the S704 option), they may be of higher spring rate then the H&R's.

      Messing around with this calculator:

      Spring rate, also known as spring constant, is the constant amount of force it takes a compression or extension spring to travel a proportionate amount of distance. The unit of measurement of rate is, lbf/in, which stands for pounds of force per inch.


      Even .1" difference makes a huge effect.

      I'm ball parking the numbers on the calculator, but to put things into perspective, to make up a 0.05" difference in spring thickness you would need to reduce the spring count from 7 to between 4-5.
      Last edited by noid; 06-19-2017, 08:32 PM.
      Your resource to do-it-yourself and interesting bmw and e30 stuff: www.rtsauto.com

      Your resource to tools and tips: www.rtstools.com

      Comment


        #4
        That's a nice calculator. Mic your wire diameters and see what you have. Wire diameter does make a big difference.

        If you just want a to see what going from 6 to 7 coils does, guesstimate and leave all the numbers the same except # of coils.

        Comment


          #5
          Originally posted by e30sh View Post
          That's a nice calculator. Mic your wire diameters and see what you have. Wire diameter does make a big difference.

          If you just want a to see what going from 6 to 7 coils does, guesstimate and leave all the numbers the same except # of coils.
          To make up for the difference in one coil, the spring would need to be ~0.02" thicker.

          I have attached how small that really is.
          Attached Files
          Your resource to do-it-yourself and interesting bmw and e30 stuff: www.rtsauto.com

          Your resource to tools and tips: www.rtstools.com

          Comment


            #6
            BMW Germany got back to me, front springs are 3686 newton at 140mm and rear springs are 5151 newton at 122.83mm.

            F=Kx

            K (spring rate) for the front is 26.32 n/mm or ~150 lb/in and rear is 41.94 n/mm or ~240 lb/in.

            Too bad H&R springs doesn't provide their spring rates, its hard to know if whats floating around on the internet is correct. Considering the H&R's are progressive, it would be interesting to know if the initial spring rate is less than OEM.
            Last edited by noid; 07-05-2017, 09:40 AM.
            Your resource to do-it-yourself and interesting bmw and e30 stuff: www.rtsauto.com

            Your resource to tools and tips: www.rtstools.com

            Comment


              #7
              There's a spreadsheet somewhere that's pretty accurate.
              "I'd probably take the E30 M3 in this case just because I love that little car, and how tanky that inline 6 is." - thecj

              85 323i M TECH 1 S52 - ALPINEWEISS/SCHWARZE
              88 M3 - LACHSSILBER/SCHWARZE
              89 M3 - ALPINEWEISS II/M TECH CLOTH-ALCANTARA
              91 M TECHNIC CABRIO TURBO - MACAOBLAU/M TECH CLOTH-LEATHER

              Comment


                #8
                Deffently add the M Tech option to list, here's one of many http://e30performance.info/viewtopic.php?t=1357

                Comment


                  #9
                  I remember re tempering leaf springs so have to ask...can the nature of the temper effect the spring rate ?
                  Seat Shocks....I have passed the baton to John Christy from Ninestitch. Email John or Garrett at ninestitch1@gmail.com

                  https://www.r3vlimited.com/board/sho...86#post4944786
                  Alice the Time Capsule
                  http://www.r3vlimited.com/board/showthread.php?t=360504
                  87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

                  Comment


                    #10
                    Originally posted by noid View Post
                    F=Kx

                    K (spring rate) for the front is 26.32 n/mm or ~150 in/lb and rear is 41.94 n/mm or ~240 in/lb.
                    That's a pretty soft spring. Compresses 150 inches for each pound. :)


                    Since you have that nice micrometer, take a measurement of the springs you have, plug them in the calc. and tell us what you find out.

                    Thanks

                    Comment


                      #11
                      I was able to pull a bunch of info together with the help of BMW Germany. Including spring rates for M3 springs, Evo 3 springs, post 09/87 Mtech springs, my S704 springs and rear springs.

                      I put it all together here for anyone who is interested:

                      These are from technical specification drawings for stock E30 springs straight from BMW Germany. The spring forces and lengths were from BMW Germany, while I calculated the spring rates to accurately compare the springs per inch of travel. Only looking at spring force does not allow you to compare springs because it only signifies the force when
                      Your resource to do-it-yourself and interesting bmw and e30 stuff: www.rtsauto.com

                      Your resource to tools and tips: www.rtstools.com

                      Comment


                        #12
                        Originally posted by noid View Post
                        I was able to pull a bunch of info together with the help of BMW Germany. Including spring rates for M3 springs, Evo 3 springs, post 09/87 Mtech springs, my S704 springs and rear springs.

                        I put it all together here for anyone who is interested:

                        http://www.rtsauto.com/e30-stock-spr...-spring-rates/
                        Nice job, thanks for the trouble. Did you happen to measure the wire diameters?

                        Thanks

                        Comment


                          #13
                          I just bought new 31331130054 and 33539061134 springs.

                          Front thickness is 13mm.

                          Fronts are true 6 coil:

                          Your resource to do-it-yourself and interesting bmw and e30 stuff: www.rtsauto.com

                          Your resource to tools and tips: www.rtstools.com

                          Comment


                            #14


                            HR OE sports, Mtech, S704 M sport suspension springs.
                            Your resource to do-it-yourself and interesting bmw and e30 stuff: www.rtsauto.com

                            Your resource to tools and tips: www.rtstools.com

                            Comment

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