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Thread: Ground Control coilover rear damping adjustment access suggestions? (E39)

  1. #1
    Join Date
    Nov 2010
    Location
    Petaluma, CA
    Posts
    239
    My Cars
    1998 540i/6

    Ground Control coilover rear damping adjustment access suggestions? (E39)

    I recently had a set of GC coilovers installed on my 1998 540i/6 and so far I love them. The issue is, I left the parcel shelf out while I drive and adjust the rears, because after everything is put back together, it seems impossible to get to the rear adjusters. Is there a way to put everything back together and still have access? Can I cut the foam over them and leave the rear deck speakers out? Is there another way?

    If not, what is considered the "best" setup for DD? A little firmer in the rear?

    I don't have the chance to get my car on the track anytime soon and really put it through it's paces so I just have to guess.

    Thanks.

  2. #2
    Join Date
    Dec 2020
    Location
    San Jose, CA, USA
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    475
    My Cars
    1994 "532i6", 1998 528iT
    There should be no reason why the track setting isn't the street setting. Maximum grip/stability and maximum comfort both stem from the same goal: minimizing load fluctuations at the tires.

    Get it right once, adjust the dampers until they're as soft as possible without allowing the car to pogo/porpoise when you shift weight by steering or throttle/brake. Then put your interior back in and call it a day.

  3. #3
    Join Date
    Nov 2010
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    Petaluma, CA
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    1998 540i/6
    Quote Originally Posted by circuit.heart View Post
    There should be no reason why the track setting isn't the street setting. Maximum grip/stability and maximum comfort both stem from the same goal: minimizing load fluctuations at the tires.

    Get it right once, adjust the dampers until they're as soft as possible without allowing the car to pogo/porpoise when you shift weight by steering or throttle/brake. Then put your interior back in and call it a day.
    Can you explain pogo/porpoise? I have never tracked my car (but plan to) and I don't know the lingo. Is there a way to test this on the street?

    Thanks for the advice.

  4. #4
    Join Date
    Jun 2012
    Location
    San Antonio, TX
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    430
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    1995 BMW M3 Coupe
    Does GC offer adjuster extenders? A friend of mine is waiting on some new ST coilovers for his E39 M5, and he ordered adjuster extenders for the rear.


    -rb

  5. #5
    Join Date
    Nov 2010
    Location
    Petaluma, CA
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    1998 540i/6
    Quote Originally Posted by RBNetEngr View Post
    Does GC offer adjuster extenders? A friend of mine is waiting on some new ST coilovers for his E39 M5, and he ordered adjuster extenders for the rear.


    -rb
    Man, if that were the case, I wouldn't be here.

  6. #6
    Join Date
    Dec 2020
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    San Jose, CA, USA
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    1994 "532i6", 1998 528iT
    Quote Originally Posted by baneoh View Post
    Can you explain pogo/porpoise? I have never tracked my car (but plan to) and I don't know the lingo. Is there a way to test this on the street?

    Thanks for the advice.
    You just need a wide road or corners or parking lot that you can do some swerving (safely) on.

    As the word kind of implies, pogo just means that the corner of the car is bouncing up and down. The damper's job is to damp that out so the suspension (oversimplified, but...) compresses once, rebounds once, and that's it. If the damping is too soft (or blown), the spring force fights the weight of the car with no damping, so that corner of the car bounces up, down, up, down like a lowrider. Conversely, if the damping is too stiff, you may feel like the suspension is controlled but the forces transmitted to the chassis from the tire (through the damper) are huge, which upsets the tire and your kidneys.

    All you're looking for is a balance - as soft as the damping can go without letting the suspension oscillate more than once. So you make a quick steering input (let's say, to the right) and the front left corner should dip down, rise back up, and that's it. Same deal for hitting bumps - compress once, rebound once, end of story.

    There's some long-winded math that I'm going to skip, but basically if you tune the dampers this way, by the time you've softened them enough you should be somewhat close to the setting that gives you the most grip and stability. You can soften the dampers even more to make initial impacts feel softer, but you'll sacrifice that lovely BMW stability for more of an old-Lexus like floating over the highway.

  7. #7
    Join Date
    Nov 2010
    Location
    Petaluma, CA
    Posts
    239
    My Cars
    1998 540i/6
    Quote Originally Posted by circuit.heart View Post
    You just need a wide road or corners or parking lot that you can do some swerving (safely) on.

    As the word kind of implies, pogo just means that the corner of the car is bouncing up and down. The damper's job is to damp that out so the suspension (oversimplified, but...) compresses once, rebounds once, and that's it. If the damping is too soft (or blown), the spring force fights the weight of the car with no damping, so that corner of the car bounces up, down, up, down like a lowrider. Conversely, if the damping is too stiff, you may feel like the suspension is controlled but the forces transmitted to the chassis from the tire (through the damper) are huge, which upsets the tire and your kidneys.

    All you're looking for is a balance - as soft as the damping can go without letting the suspension oscillate more than once. So you make a quick steering input (let's say, to the right) and the front left corner should dip down, rise back up, and that's it. Same deal for hitting bumps - compress once, rebound once, end of story.

    There's some long-winded math that I'm going to skip, but basically if you tune the dampers this way, by the time you've softened them enough you should be somewhat close to the setting that gives you the most grip and stability. You can soften the dampers even more to make initial impacts feel softer, but you'll sacrifice that lovely BMW stability for more of an old-Lexus like floating over the highway.
    Awesome, thank you.

    I am going to try and take it to the track for a weekly drag and drift so I can get it out on the skidpad. I think I am damn close though. I love these coilovers, but the lack of a rear adjuster is wack.

  8. #8
    Join Date
    Dec 2020
    Location
    San Jose, CA, USA
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    475
    My Cars
    1994 "532i6", 1998 528iT
    I guess coming from an E34, I just lift the seat bench and do my business lol, it's annoying to adjust all the time but doable once in a while. If you're taking it out to a skidpad day, you'll be busy working the wheel so use a GoPro aimed at the wheels to track what your suspension is doing

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