Critical damping, under damping and over damping

Discussion in 'Car Modding' started by mantasisg, Nov 24, 2019.

  1. mantasisg

    mantasisg Registered

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    I need some help, I am learning how to find and manage these damping ranges. I would be very happy for any hints, information or formulas how to calculate these. Currently I am often having issues with damping when I go for soft setups, I'd like to find out what proper values would be for springs, dampers and anti roll bars to battle oscilations, but still maintain soft chassis. Also should I take geometrcal chassis stiffness into account (I guess I should), and how should I do that ? Are there any basic design rules ? Should there be some sort of specific frequency differencies of front vs rear oscilations ? Could it be true that some oscilations may be a tradeoff for very soft car setups, and isn't possible to fully damp without increasing stiffness (and killing body roll), it can be seen on lots of classic race cars and road cars up till late 90s that are apparently very very soft.

    Thank you.
     
  2. John R Denman

    John R Denman Registered

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    Books have been written about damping, but here is a simple way to see it.
    Weight transfer front-rear takes time and that time is controlled by the dampers. Sure it all happens quick so here's a few ways to gauge that.

    Under braking the rear gets light; softer rebound allows the rears to stay planted longer, giving the driver a tad more time to react to avoid looping the car.

    Softer rear compression allows a little faster droop under acceleration which gives a little more time to respond to over throttling on the exit of a turn. To a point anyway as once you've hit the bumpstops the damper settings are a bit nullified.

    Big bumps like Sebring tend to favor a tad more compression to stay off the bumpstops so much, and likewise a bit less rebound, both ends.
     
  3. Emery

    Emery Registered

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    Classic slow damping ratio is 60-70% for performance cars. This gets thrown out the window when there is significant downforce as you essentially have a sprung mass that changes with speed. I like to think of rebound damping as the control for the opposite end of the car and adding compression as turning up the liveliness of the same end of the car.

    Fast damping ratios are usually chosen so that one can hit kerbs without upsetting the car. Definitely worth looking at shock dyno plots to find the ballpark.

    Ride quality is irrelevant to racing, but, when it is, then you want to avoid heave & pitch and pay attention to the wheelbase resonant frequency at the average speed for particular tracks & bumps. As natural frequency comes up to 2+ Hz, then heave & pitch damping quit being important to ride quality (aka flat ride).

    http://farnorthracing.com/autocross_secrets6.html (and the rest of the site) is a good read even if you sometimes disagree with the author.

    https://www.youtube.com/user/SuspensionTruth/videos Fat Cat Motorsports channel on YouTube is another viewpoint.
     
  4. lordpantsington

    lordpantsington Registered

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  5. mantasisg

    mantasisg Registered

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    Big big thanks !

    This is already more stuff than I expected. And I am immediately starting to understand suspension better. All this material will keep me learning for a while. I will probably have even more questions after, hopefully. The more you learn, the more questions you have :D
     
    Emery likes this.
  6. Dave^

    Dave^ Registered

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    There's an app available on the play store for Forza (yes, yes, I know!) Which give you ideal (?) setups for cars depending on weight, tyre size, drivetrain, etc.

    I doubt the actual numbers would correlate well with rF2, but you may get an idea of what 100kg more/less does to the relevant suspension settings for example.

    Might be worth a look.
     
  7. mantasisg

    mantasisg Registered

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    Forza ? haha But yeh, i believe useful stuff can be learned even in backgrounds of Forza, I'll look at it.

    Meanwhile, perhaps somebody has to suggest comfortable and easy to use app to visualize camber and toe gains, as well as other geometry stuff ?
     
  8. Emery

    Emery Registered

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    There's nothing free that I'm aware of. In theory it should be possible to write a spreadsheet to generate a graph, but the 3D geometry tends to discourage that. On the other hand, a 2D version is less daunting and might be adequate for the camber changes...hmm, might even be adequate for the toe changes now that I think about it.
     
    Gilles Benoit likes this.

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