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Thread: Supplied BC coilovers 6kg/mm spring rate, too soft for track e30m30?

  1. #1
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    Supplied BC coilovers 6kg/mm spring rate, too soft for track e30m30?

    Given the extra weight in the front of my car due to the M30B35 it *might* not be ideally sprung right now and after some google searches of rates and conversion tables it seems I have the 6kg/mm (315lb) springs all around where it seems that a far heavier 550lb ish spring seems preferable for your track day e30 rear end with the 315lb retained for the front.

    Springs are cheap, I'm willing to do some trial and error to achieve that go kart handling I so desire.

    So which way do I go??

    How long IS a piece of string?

    Someone has already told me I could comfortably double my spring rates they are so low, but his point of reference is a solid rear axle datsun 1200 race car he helped set up and an extensive Honda background so I'm looking for BMW based opinions.

    Simon Harrex of RX automotive has already told me an e30m30 will turn but has stated that spring rates are critical to set up, but he's too shrewd to give up his trade secrets when I could be paying him to set the car up for me (and I'll learn nothing).

  2. #2
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    i would have thought thats quite low for the front.
    I run 12kg up front and 8 or 10 in the rear

    Depends how well the damper can control the spring.

    You are right 60mm ID Eibach springs are about 200 a pair.

  3. #3
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    What's the car doing where it's not handling properly.

    Understeer?
    No traction out of corners?

    What's your alignment spec u run on the track?

    What tyres are you running?
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  4. #4
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    for track work you'd step up the stiffness a bit 6kg is more street oriented weighting

    The reason the e30 is supposed to use a stiffer rear spring is because of your horse kart suspension, the semi trailing arm horse kartness applies more angular mass on the spring, than say if you have a true coilover acting in the rear.

    there are a lot of factors when determining spring rates tho. Ideally you design spring stiffness to minimise or delete sway bars, but if you're not going to pay for the engineering for that than go stiff, 10/12's or 8/10's and use sway bar and alignment to fine tune the suspension.

    Burkey you run a true coilover at the rear don't you?

    I think you need to keep in mind are you actually a good enough driver to take advantage of the suspension tweaks that pro drivers use to gain 1/10ths of seconds, or will you even be able to push the car hard enough where any flaws are that obvious, do you expect you'll even know how to tell what suspension flaws are holding the car back?

    I say this because realistically if you went with a say stock standard 6/8 setup that was properly corner balanced and have the camber/caster/ toe setup by someone knowing what they're doing I think'd you be pretty damn happy with the handling
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  5. #5
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    Thanks for the response guys, I know its been weeks since I asked about this but here is the follow up.

    GazM3 wrote:
    What's the car doing where it's not handling properly.

    Understeer?
    No traction out of corners?

    What's your alignment spec u run on the track?

    What tyres are you running?
    Understeer, has loads of rear traction but more throttle means more understeer on corner exit.

    Zero toe on the front and 3.2 deg neg camber and 2 degrees of toe in and neg camber on the rear.

    Federal 595rsr tyres brought in 2012. Some tell me they are poo, some tell me they need higher tyre pressures to work given they are a road tyre.

    mfyoung1086 wrote:for track work you'd step up the stiffness a bit 6kg is more street oriented weighting

    The reason the e30 is supposed to use a stiffer rear spring is because of your horse kart suspension, the semi trailing arm horse kartness applies more angular mass on the spring, than say if you have a true coilover acting in the rear.

    there are a lot of factors when determining spring rates tho. Ideally you design spring stiffness to minimise or delete sway bars, but if you're not going to pay for the engineering for that than go stiff, 10/12's or 8/10's and use sway bar and alignment to fine tune the suspension.

    Burkey you run a true coilover at the rear don't you?

    I think you need to keep in mind are you actually a good enough driver to take advantage of the suspension tweaks that pro drivers use to gain 1/10ths of seconds, or will you even be able to push the car hard enough where any flaws are that obvious, do you expect you'll even know how to tell what suspension flaws are holding the car back?

    I say this because realistically if you went with a say stock standard 6/8 setup that was properly corner balanced and have the camber/caster/ toe setup by someone knowing what they're doing I think'd you be pretty damn happy with the handling
    Is that a 6kg front 8kg rear set up you speak of?

    That sounds doable with what I have here at home.

    lol good enough driver for pro tweaks for 10ths, probably not. I'm still at the finding whole seconds with set up phase.

    I had the camber/castor/toe set up by a guy that does the set up for local e30 racers in October last year and he rubbished my rear camber /castor adjusters but cutting 1:14 laps in stinking hot November it felt good and balanced, but 1:09 laps in a cool and pleasant June felt understeery.

    Burkey001 wrote:You are right 60mm ID Eibach springs are about 200 a pair.
    I have these springs in the shed and after placing a 10kg plate on the spring and measuring the sag of 1.5mm with a steel rule and comparing it to the 5mm of sag from the BC beehive spring with the 10kg plate on it I'm going to conclude that these KYB springs from Matt Dumesnys dads M3 are a better prospect than the BC 6kg springs.


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