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    Rear suspension setup

    I am hoping to increase my rear traction, as I am having a hard time getting power down. Car is setup with a GC coilover setup, 440/660 spring. Front IE bar on soft with M3 mounts, no rear bar. I'm running 245/40/17 RE71r's. 32/30 psi. Even in a straight line, I'm able to get the wheels to slip on aggressive gas. Now, I'm running a 270hp N52, but nevertheless, seems like the rear should be grabbing better. I'm running -2.5 in front camber, -2.5 in rear. I'm thinking maybe I should reduce the rear camber to get the tire more square with the pavement. Given the high hp. I'm running, seems like I would gain more net in an autocross setting. Anyone have any advice? I really hesitate to increase rear spring, but anyway, the power induced camber change is pretty noticeable.

    #2
    Your spring rates are quite a bit too low to eliminate the rear sway bar in my opinion. Put in a 19mm rear bar or up your spring rates, thatís a street spring rate setup you are running anyway.

    As for camber, a good target is typically -2.0 in rear

    My car weighs 2250#, I run 700/900 spring rates, and I make 280rwhp, no rear end grip issues. Also, no rear sway bar

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      #3
      Rear bar I would say is more determined from your split F/R. #200~ on mild spring rates I believe is a vague rule of thumb


      What is your rear toe?


      Probably could drop rear camber to 2.25-2.0



      Zach@Zakspeed.us

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        #4
        Moatilliata May be right but my experience is also that you really need quite a high spring rate to make elimination of the rear bar effective.

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          #5
          Loosing traction in strait line I would check toe. I would dig for 0 to 1/8 in and see how that goes. I prefer something closer to 3/32 to 1/8 IN

          If that is in, then maybe fool the the bars.
          Zach@Zakspeed.us

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            #6
            Thanks guys. So I think I will take the rear camber down to 2-2.25 and see the results. I am running about 1/8" toe in on the rear. I have the stock rear bar installed but not hooked up, so I guess I can experiment with that as well. M3, I think you are right about needing more spring, but its something I would like to add last if these other changes don't resolve the problem.

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              #7
              One more thing.....every once and a while, I get rear wheel hop on mid-turn and exit. Not sure if a bump is starting the process, or if its some suspension dynamics going on as I apply throttle?

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                #8
                Although I have an E30 M3, my experience may be helpful for you. I am running a GC setup with SA Konis and 550lb front springs and 750lb rear springs with 22mm front and 19mm rear sway bars. Tires are 225/50R15 Pirelli Troefo R. On the track I found I needed to set my rear Konis to full stiff and then back off 1/4 turn. I run my car at Portland Int'l Raceway which is a fairly smooth track with a couple of corners that are bumpy on exit.

                I don't experience any rear wheel hop and can lay the power down throughout the corner. Car is neutral to slight oversteer. .
                1990 M3

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                  #9
                  Iím assuming you have Poly subframe bushings, diff, and at least new trailing arm bushings?

                  How old are the koniís?
                  Zach@Zakspeed.us

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                    #10
                    Yes, all new poly ta bushings, and Condor subframe and diff. Koni's a couple years and maybe 500 miles on em. I'm about half a turn from full stiff on the Koni's.

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                      #11
                      Have you corner balanced the car?
                      Zach@Zakspeed.us

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                        #12
                        No, car never corner balanced.

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                          #13
                          Iíd give that a go. I Doubt itís it but nice to have a flat platform to start with.


                          How did you check toe in?

                          Did you buy the kit G.C. kit new?

                          Are youre eccentrics TIGHT?

                          Zach@Zakspeed.us

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                            #14
                            Yes, I am thinking the same thing on looking at the rear camber/toe adjusters. GC kit is new, and toe was checked with plates....might investigate that a little more as well. Anyway, I appreciate the help, and will see what turns up.

                            Comment


                              #15
                              If loose, I also have a theory in why people have problems.

                              A longated hole in theory has only about 30% of the clamping area. Thatís if the person longating the holes didnít get sloppy. Next most trailing arm bushing sleeves are aluminum, so now that 30% clamping surface mushrooms the aluminum and the bolt comes loose. And people donít crank the shit out of them!
                              Zach@Zakspeed.us

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