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E36 M3 5 lug conversion, roll centre?

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    E36 M3 5 lug conversion, roll centre?

    Has anyone ever seriously looked at the various suspension motions when using this conversion?

    I've seen plenty of guides which imply it bolts together, and even some with alignment sheets and pictures of the wheel in the arch to show that the static alignment is acceptble, but has anyone ever really looked at:

    • Bump steer
    • Camber change
    • Roll centre height

    Given the price of the parts, I'd like to know the answer before settling on it, which means modelling the whole suspension. In the name of 'standing on the shoulders of giants' and all that, has anyone started or finished a similar exercise and happy to share their findings?


    Thanks


    Al

    #2
    You need to be an engineer to graph all the angles of the suspension and get an imagery of the theoretical roll center. Then there are so many applications (all 96+ components; 95 CA with offset CAB and 96+ spindle, non-M components, etc). So many different variations out there. Good question, but I have a hard time believing that someone drew out the geometry and all the angles to gather a roll center answer to this swap.

    Comment


      #3
      Yeah I just can't believe that for all the conversions that have been done and the sheer number of recommendations for it, no one has actually checked it works properly.

      Comment


        #4
        I think everyone knows (or should know) the E36 swap does not give you proper geometry.

        Front geometry is not that hard to model. You can use a protractor with magnetic base to get the angles.

        I dont think the RC would be worse with the e36 stuff. The castor is most likely the most messed up.
        Attached Files
        -Nick

        M42 on VEMS

        Comment


          #5
          I understand how to do the calcs, I just dont have the parts. Plenty of people are running this conversion but it all seems to be a bit "suck it and see" without much actual research.

          "I've fitted it and havent crashed yet" seems to be good enough!

          Before deciding which of about 6 options to take, it would be handy to know what the outcome would be but it seems that unless I take all of them in turn, no one has any useful data

          Comment


            #6
            Agreed. I have the stock geometry modeled, but dont have the other parts so Ive never modeled them. Im curious to know how big the change really is.
            -Nick

            M42 on VEMS

            Comment


              #7
              Indeed, there is clearly no ideal solution (apart from E30 M3 parts) which certainly in the UK are simply impossible to find.

              I'd love to see all the plots for the E30, E30 M3, E30 with E36 M3 retrofit etc for comparison.

              Comment


                #8
                Originally posted by alistairolsen View Post
                Plenty of people are running this conversion but it all seems to be a bit "suck it and see" without much actual research.

                "I've fitted it and havent crashed yet" seems to be good enough!
                I think you may be overestimating the base a bit.
                I would bet 90% of the guys who swapped E36 parts onto their E30s have no idea what Roll Centre is, or care, or wouldn't know what to do if they knew it was good, bad or ugly.
                They did it to get access to a wide variety of 5x120 wheels to show off at Cars and Coffee.

                If you look around this site (and others) 60-70% of the cars wheels don't even fit even remotely right let alone has anyone thought about Roll Centre. You have cars with fucked camber setting to get the wheels to fit, grossly wrong offsets, ride heights set by eye so they look good, etc.
                Last edited by JimmyP; 09-29-2017, 08:32 AM.
                Jimmy P.
                87 E30 M3 Prodrive British Touring Car
                88 E30 M3 Zinnoberot - Garage Queen
                88 E30 M3 Lachsilber - SCCA SPU #98
                92 M Technic Cabrio - S14 Powered!
                98 318Ti Morea Green
                04 325i Touring Alpine
                04 Ford F350 Dually Tow Machine

                Comment


                  #9
                  I didnt like to say....

                  Comment


                    #10
                    That was edited to be kind.
                    Jimmy P.
                    87 E30 M3 Prodrive British Touring Car
                    88 E30 M3 Zinnoberot - Garage Queen
                    88 E30 M3 Lachsilber - SCCA SPU #98
                    92 M Technic Cabrio - S14 Powered!
                    98 318Ti Morea Green
                    04 325i Touring Alpine
                    04 Ford F350 Dually Tow Machine

                    Comment


                      #11
                      So what’s the issue with the E36 suspension in an E30?

                      I understand the geometry is “not proper” - so what’s not proper about it?

                      Does it result in poor handling? Some weird handling dynamics?

                      I’m not arguing or disagreeing, just trying to find out more precise info.

                      Comment


                        #12
                        the tie rod balljoint's pivot point is about an inch lower on an E30 strut than an E36 spindle, which influences bump steer.

                        the relative position of the virtual axis of rotation of the front wheels is also completely different from stock e30 *and* from how the suspension is mounted in an e36, as are the camber and caster curves, which implies that it doesn't work as engineered.

                        unclear what the physical effects are.
                        cars beep boop

                        Comment


                          #13
                          Originally posted by kronus View Post
                          the tie rod balljoint's pivot point is about an inch lower on an E30 strut than an E36 spindle, which influences bump steer.

                          the relative position of the virtual axis of rotation of the front wheels is also completely different from stock e30 *and* from how the suspension is mounted in an e36, as are the camber and caster curves, which implies that it doesn't work as engineered.

                          unclear what the physical effects are.

                          Interesting. You got my attention. Would like to know more!

                          Comment


                            #14
                            In general camber impacts your tire contact patch through the range of motion. Castor impacts your high speed stability and ability to return to center.
                            -Nick

                            M42 on VEMS

                            Comment


                              #15
                              If you want to get technical there is a piece of software called "optimum k". The free version i belive has all the features you just cant save it. All kinds of nerdy ways to graph suspension things once you input your suspension dimensions in.

                              http://www.optimumg.com/software/optimumkinematics/

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