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What's better? Divorced rear suspension or non?

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    What's better? Divorced rear suspension or non?

    As I continue my quest to make my convertible more and more track-like (because racekor duh) I was wondering if there any solid arguments for non-divorced over the stock divorced rear set up? Right now I'm running Billy HD's in the rear with German Engineering springs and adjusters.

    Spring rates and shock rebounds aside. What is fundamentally a better system for our chassis? I'm assuming the West German Engineers know a thing or two and went with divorced for a reason?

    Does it even make that much of a difference? These are the questions that haunt me at night.
    Last edited by Brezzi; 09-13-2016, 12:38 PM.

    #2
    My understanding is that the "divorced" design mostly has to do with packaging. If you tried to put real coilovers in the rear, you'd need to move the wheels further out...which you can't do without cutting/flaring the rear quarter panels. You might also need to strengthen the rear shock mounts, which would now carry a much more significant load.

    If you did that, you'd have a rear suspension that would almost certainly be better. More linear relationship between front and rear spring rates. Less strain on the rear subframe and mounts.
    sigpic
    1987 Mercedes 190E 2.3-16: Vintage Racer
    2010 BMW (E90) 335xi sedan: Grocery Getter

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      #3
      Originally posted by Emre View Post
      If you did that, you'd have a rear suspension that would almost certainly be better. More linear relationship between front and rear spring rates. Less strain on the rear subframe and mounts.
      does this really matter? don't you just compensate for the difference in motion ratio by running a stiffer spring? effectively, it's the same at the wheel, is it not?

      One benefit I can think of is having more spring travel in the rear before hitting coil bind. on a lowered E30 there's really not much space for a spring. It's not good to bottom out your rear springs and end up with an infinite rate. Also there's often not enough room for adjustment with threaded perches - many people just take them out. Mine are still in but they are all the way at the bottom.

      but really, to 98.9% of people it's probably not worth the hassle.
      Build thread

      Bimmerlabs

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        #4
        Originally posted by nando View Post
        does this really matter? don't you just compensate for the difference in motion ratio by running a stiffer spring? effectively, it's the same at the wheel, is it not?
        Sure, but it's just easier to calculate and tune. Probably cheaper, too, since you could use regular, full-length, linear race springs all around (like the circle track guys). Not a big deal really, but maybe your life would be a little easier.

        Originally posted by nando View Post
        but really, to 98.9% of people it's probably not worth the hassle.
        Agreed. Totally not worth it.
        sigpic
        1987 Mercedes 190E 2.3-16: Vintage Racer
        2010 BMW (E90) 335xi sedan: Grocery Getter

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          #5
          Add to that, you'd get a better relationship between measured spring rate and
          wheel rate. The scissoring action of the stock spring means that the
          spring behaves ever- so- slightly differently than designed.
          I use shims instead of a sleeve, and that gave just enough extra room
          to get a 5" spring back there.

          but really, to 98.9% of people it's probably not worth the hassle.
          yeah. I'd say 99.2%.
          However, if you're starting from scratch, a set of good shocks and
          several sets of 5" springs are NOT a trivial expense....

          I did adapt to rear coilovers on the 2002 race car when I changed to E21 trailing arms.
          It helped- fractionally. The spring rates and sizes
          are still different than the front, but coil and shock bottoming went away.
          Shock tuning got easier, too, since a multi- adjustable coilover shock's significantly cheaper. And since the 2002 uses a 5" spring, there wasn't a weight penalty.

          t
          now, sometimes I just mess with people. It's more entertaining that way. george graves

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            #6
            Originally posted by TobyB View Post
            Add to that, you'd get a better relationship between measured spring rate and
            wheel rate. The scissoring action of the stock spring means that the
            spring behaves ever- so- slightly differently than designed.
            I use shims instead of a sleeve, and that gave just enough extra room
            to get a 5" spring back there.



            yeah. I'd say 99.2%.
            However, if you're starting from scratch, a set of good shocks and
            several sets of 5" springs are NOT a trivial expense....

            I did adapt to rear coilovers on the 2002 race car when I changed to E21 trailing arms.
            It helped- fractionally. The spring rates and sizes
            are still different than the front, but coil and shock bottoming went away.
            Shock tuning got easier, too, since a multi- adjustable coilover shock's significantly cheaper. And since the 2002 uses a 5" spring, there wasn't a weight penalty.

            t
            You said Scissoring.. :nice:

            Isn't Mina's (formally Greg Miller's) car set up this way? I seem to recall looking at the rear suspension when I was pitted next to him at the Historic's in 2014 and it using Circle Track style shocks/Coils.
            1991 325i MT2 Touring (JDM bro)
            2016 Ford Flex
            2011 Audi A3 - wife's other German car

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              #7
              It slices, it dices, it even says 'maa- maa'

              Mina's car better not be. In Pro3, that's cheating. Stock attachment point language.

              I know Greg had stock rear suspension...

              It would be wonderful if that were true ... I would protest her in a heartbeat,
              if only to show her it can be done!

              hee

              t
              now, sometimes I just mess with people. It's more entertaining that way. george graves

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                #8
                You may want to look at it again. I distinctly remember the shocks were not stock style and mounted completely different.
                Last edited by djjerme; 09-15-2016, 10:48 AM.
                1991 325i MT2 Touring (JDM bro)
                2016 Ford Flex
                2011 Audi A3 - wife's other German car

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                  #9
                  That's awesome.
                  Wish I could go to the Ridge with my camera this weekend.
                  It's time to lay down a Benjamin!

                  t
                  now, sometimes I just mess with people. It's more entertaining that way. george graves

                  Comment


                    #10
                    i once saw an e30 that had rear coilovers AND the stock spring in place. double the spring rate, less stress on the strut tower. I think it was a R3v OG - Art maybe?

                    i didnt think it took a whole lot of fuss to make the coilovers work, but needed narrow, low offset wheels. 7.5" wide et0 equivalent or something. so basically any gain to be had with the better coilovers is lost by having to run stretchy tires to make them fit under the rear fenders. so like someone said, pointless without fender widening of some sort. there are much better ways to improve your rear suspension besides this.

                    Comment


                      #11
                      What's the point?
                      I asked a similar question in this thread, where OG Trent posted his setup but so did someone else: http://www.r3vlimited.com/board/show...=101207&page=3

                      Anywho:



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                      Talked to VAC. You need extensive shock tower reinforcement and not a mod recommended on a street car. Otherwise it is very likely that you may damage the chassis.

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                        #12
                        Hey guys just wanted to say thanks for the great discussion and all the info. I've decided to stick with divorced for now. Maybe if I build something just for the track or something crazy extreme that I don't need to get me from point a to point b from time to time.

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                          #13
                          I know this is resolved, but I have some pics of true rear coils on my one e30 here:





                          Second pic somewhat shows the rear strut tower boxes built to withstand the true coils. They are fully enclosed made from 3/16 mild. These are tied into the cage downbars. They are also tied into the secondary diff mounts that go through the floor of the trunk.

                          If anyone has any questions on whats required to use this GC rear set-up like I have here, I can shed some light on it. I can also post more pics of this GC set-up if any one wants to see it.

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                            #14
                            Originally posted by yamahammer View Post
                            If anyone has any questions on whats required to use this GC rear set-up like I have here, I can shed some light on it. I can also post more pics of this GC set-up if any one wants to see it.

                            I'd like more info. I've been looking into a solution recently, and my towers are already boxed and tied into the cage, so I'm good to go. I really need to get more spring rate back there, and if I go any higher I feel like I'm just going to keep twisting up trailing arms. My car squats 3"+ under load. It really screws up my acceleration on corner exits.
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                              #15
                              Will post some stuff later today.

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