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  1. #1
    Andy
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    Suspension? Spring Rates and Sways....

    Hey all,
    Just got done doing the Evolution Autocross School today! Having taken the EvoI & II schools I was totally excited to take the Challenge school which included having the bottom of my windshield taped to totally obstruct my view of the first 60 feet in front of my car and having Mark Daddio, one of the top, top autoxers in the country do a few laps in my car and set a time for me to beat. People pushed hard run after run with cones flying everywhere but on one could beat the times he set in their own cars.

    Anyway, one of the things we talked about was how tail happy my M5 is. While my suspension set-up is miles above what is was with the SLS system, I woudn't mind a little more grip in the rear for this season. Here's my current set-up:

    GC Coilovers
    Koni SA Yellows
    450/350 lbs/in springs f/r
    225/45 17 tires all around

    My car is going into the shop on Monday to rework the front mounting points for the spring perches so I can get my car a little lower while also getting in some longer springs for more suspension travel. So, this is a great opprotunity for my to play around with spring weights and suspension settings.

    What spring rates are you guys with coilovers running? Any thoughts on how to get a little more grip in the rear? Perhaps going to much heavier rear springs and ditching the rear sway bar?

    TIA!


  2. #2
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    I wouldn't ditch the rear sway, adds stability to>

    ..and strength to the whole rear end. RoyW should be the guy to ask, but how about going with a stock rear sway and an adjustable front (like ST or Dinan) set on medium/stiff? That should dial out some of the rear bias. Have you been up and down the matrix of tire pressures/temps? That would be an easy way to tune things. Get an accurate tire temp and pressure gage so you can build a spreadsheet. Not sure exactly where you are located, but remeber that HP parking lot me met in for Kimball's (corner of 495 and RT119)? That building is totally abandoned now. You could set up a couple cones way in the back, and no one would ever know you were there.

    Bob88 ///M5, RIP

  3. #3
    Andy
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    Not oversteer so much as....

    The car actually understeers with my current set-up. What I was looking for was to see if there are changes I can make to get more traction while powering out of turns or in transitions.

    On another note, the guys took off my front struts and found I had totally blown the front Koni's from ground control after 2 seasons of driving. 6-8 weeks for a rebuild <sigh> so it looks like I'm putting some bilsteins up front temporarily while the koni's get rebuilt..... and all the bushings are shot in the front suspension and my diff is leaking.... Driving is suddenly getting really expensive.

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    Stiffer rear bar dials out understeer.

    88 ///M5, RIP

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    Re: Suspension? Spring Rates and Sways....


    One of the easiest ways to get the tail to stay in,and get more traction is simply run the rear tires 5lbs below the fronts.Did it for years at driver's school.Drastic difference. Rags535
    '97 Infinity Q45t BMWCCA#5217
    '86 535i/5 SIG#143
    '86 535i CARTECH turbo (sold)

  6. #6
    Andy
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    Already do + Update

    At the track I run about 3-5 psi lower tire pressure in the rear than the front.

    My first HPDE of the season was last week and the only changes I made were to have the car cross-balanced and lowered about in inch which had a corresponding increase in rear camber giving me a total of about -1.5 degrees camber in the rear. Car felt much better with the lower roll center and increased camber.... so much better that I was more comfortable pushing the car to the point that I lost the rear and spun for the first time at a non-auto-x event.

    Overrall I still think the car sways a little more than I like in transitions so I'm going to see about going to higher spring rates all around and also adding more camber up front.

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