Suspension basics, adjusting for rough tracks?

Discussion in 'General Discussion' started by davehenrie, Mar 23, 2021.

  1. davehenrie

    davehenrie Registered

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    I wonder if someone can give some basic guidelines on how to setup a car for a rough track? Not necessarily Sebring, but perhaps Bridgehampton?
    Springs? softer or stiffer?
    shocks/damper? fast vs slow rebounds, front and rear....I'm looking for a starting point to better grasp what changes I should be making to control the car better.
     
  2. Lazza

    Lazza Registered

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    Generally speaking, softer springs. That will generally mean softer (lower) damping.

    If you consider a bumpier surface to be lower grip on average, normal logic would suggest moving the rear a bit further to 'soft' than the front to retain some control.

    But obviously this is all very general advice.
     
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  3. mantasisg

    mantasisg Registered

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    It is simple - just make tires as hard as possible, reduce rideheights to the minimum, make stiffest possible springs and shocks, stiffest possible antiroll bars, use most possible amount of packers, use maximum downforce for biggest possible reaction forces from hitting bumps, use maximum amount of toe angles regardless negative or positive, use as little as possible caster for extra instability, and also make sure that tires are simulated to be as difficult as poissible so driving becomes really bold and difficult over any kind of instability as opposed to arcadishly simulated tires which literally makes everything that happens to car nearly meaningless.
     
  4. Remco Majoor

    Remco Majoor Registered

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    Love how one simple question can get mantis a mental breakdown

    Anyways, fast bump lower seems to work very well. Slow bump (on Sebring for example) I still keep relatively high, due to the amount of quick turns.
     
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  5. Sim_Player

    Sim_Player Registered

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    depending on tracks "flatness " or smoothness i pick my spring rates.
    general rule of thumb is
    the smoother and flatter the track then stiffer springs
    and the rougher and slower the track then softer springs

    in your case i would suggest picking springs rates that are softer.
    To start you pick either lowest available springs or just 1 click or 2 click more from lowest springs.

    if i'm not wrong, softer springs(and ARB) will mean more tyre movement or more contact patch variation i.e more changes in camber and toe. for example under compression softer springs will gain more camber so you have to start with more STATIC camber.
    The stiffer the springs and arb is the more precise you can be with your static camber.

    why softer springs on bumpy , rough surface ?
    because it allows the wheel/tyre to follow the surface OR to "deform" with the given road conditions.

    All you need to know is when to stop going down on springs rates, you just need enough softness to gain proper tyre contact to surface. too much soft isn't going to help after this point.

    •Damping

    •Slow damping:
    general rule of thumb, stiffer springs extend/ rebounds harder than softer springs. so you will need more (stiffer) slow rebound as you go up the springs rates.
    softer springs are easy to compress so you need stiffer slow bump.

    so if your springs rates are on softer end of spectrum then i suggest you start your slow bump value from top(stiffest) then lower as you wish
    AND
    start slow rebound with lowest value then add more stiffness , if you want.

    •Fast damping:

    The bigger the height of a kerb or bump is the lower F.bump value you will need. you just need enough softness so that car doesn't lift/ go airborne. too much soft F.bump you will hit bumpstop which is not good for performance over kerbs or bumps.
    similarly since the kerb is taller the tyre will also need to "fall" off it quickly so in this case you will actually have to lower the F.rebound as well. (again not too low otherwise tyre will bounce back up after hitting the surface causing oscillations)

    for example the kerbs at last chicane at suzuka, quite high kerbs so here above mentioned tip will work.

    under "normal" small scale bumps and kerbs you generally want F.rebound to be HIGHER than F.bump to stop oscillations.

    Also fast damping is dependent on springs rates as softer springs compresses easily you probably need to increase stiffness of F.bump as well to stop too much suspension travel.and lower the F.rebound so that tyre can follow or drop to ground quickly (too high F.rebound in combination with softer springs will keep tyre in air , you will hit ground even harder this way.)

    similarly, stiffer springs will rebound harder so you will need even more F.bump to stop tyre hitting ground like a basketball, making the tyre bounce back up again..,oscillations.
    and F.bump will go down as stiffness of spring increase or car will be jumping around.
     
    Last edited: Mar 23, 2021
  6. Highlandwalker

    Highlandwalker Registered

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    Try reducing spring rate and increasing packers, I find this helps with rough tracks. The reduced spring rate absorbs the bumps and the increased packers reduces suspension travel so avoids the car bottoming out. This is usually the first thing I try.
     
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  7. mantasisg

    mantasisg Registered

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    Technically many of those things are true and untrue, because specific details are different. Speaking of tracks, Bridgehampton is more about damping sprung mass, Sebring is more about damping unsprung mass. Different undulation scales, different way and patterns of undulations and so on.... Not to mention simply layout and elevations. You just have to take the car, drive it, understand how it worked and if it could be adjusted to be better. Altering stiffness of a car will also alter its mechanical grip in turns, braking and accelerations. There is not that much to learn from generalizations. Although, I think Davehenrie created this more for discussion.

    Secondly, cars are very different... for example different, mass, different ground clearance, different aero, different speeds, different wheels and so on. What is stiff, or soft ? That also depends on each car and even a driver. Perhaps to me, a guy who loves more chassis motion a suspension rate that barely moves a car will appear as extra stiff, while other guy who loves hyper responsive car it will count as soft suspension rate.

    But hey this is simracing 2021, I guess we speak about latest GT3 cars then.


    Thats one interesting bit. IIRIC somewhere I saw the opposite being told. But iiric it depends on bump, but not sure... The thing which happens with softer spring is that unsprung mass falls more easily into a dip, while harder sprung wheel would instead fly over the dip. Thats not intuitive. Thinking about it a bit more, of course in turn, braking of acceleration it is more ideal to have wheel pressed firmly to surface as continuously as possible, but in terms of comfort at high speed in the straight it could turn out comfortable to have wheels flying over dips :D And dips, I'd say will always be more likely to form on the road than a bump.

    Bump and dip
    [​IMG]
    Aaaand, I think I learned it from this guy:


    Thats interesting, makes sense. However once packers are going to be hit, the force of the bump will transfer to the chassis, that is not great. Similar to bottoming out. Making suspension softer, and reducing the travel is of course making it more likely to happen. But I suppose if it doesn't happen, then it is good to go like that.

    I like older cars, I like how they has more practical, more true to public roads rideheights. It allows more suspension travel with greatly reduced possibility of bottoming out. Giving more comfort, grip and more show:

    [​IMG]


    I am not mantis, and it wasn't mental breakdown, it was humour.
     
    Last edited: Mar 23, 2021
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  8. Sim_Player

    Sim_Player Registered

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    Yes, i agree with this. I think this is not ONLY because spring being soft, IMO the softer springs follows the dip because more of the car mass is "resting " on it. This is why i believe softer springs will fall into dips.
    Softer springs has more potential energy (car's mass) stored hence it has more rebound available.
    This is maybe why stiffer springs tyre will skip over it because it is not being compressed enough to extend that far.
    If both soft and stiff spring has same travel they will fall into dip but will require different forces.

    Edit: not only the car's weight but also the weight of wheel and tyre will be pulling/extending the softer springs more in a dip.

    This just my theory, i could be wrong.
     
    Last edited: Mar 23, 2021
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  9. Highlandwalker

    Highlandwalker Registered

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    The packers being made of a hard rubber type material or similar means it's a softer impact than the car bottoming out which also means the shocks may still has an effect which also means the tyres are having an effect on the rod instead of the bottom of the car. When I use to do Moto-X I tended to use a softer spring and then adjust the preload on the spring for the conditions of the track. I know fairly extreme suspension travel is involved with Moto-X but the overall idea is to keep the wheels in contact with the track.
     
  10. Sim_Player

    Sim_Player Registered

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    One thing i noticed couple of times is that people recommend lower/softer damping with softer springs.
    i assume by "lower damping " they are talking about both BUMP and REBOUND damping.
    Now this goes against my first post but after thinking about it here is my updated theory.
    (my first post still is valid just to be clear)

    The stiffer springs will travel less for same force relative to softer springs
    BUT
    in my mind the stiffer spring will also get "settled " or reach its travel for given force QUICKLY !, i.e the bump/compression will happen quickly

    •for example >

    lets say for FORCE X

    1. softer springs travels 10 mm in 2 seconds

    2.For same force stiffer springs travels 5mm BUT in 1 seconds ( so it finishes the travel/compression 1 seconds earlier than softer spring)

    This could explain why you might wanna increase the slow bump ALONG with slow rebound with stiffer springs.
    this will decrease mechanical grip further BUT in aero cars you MAY want to stiffen the SLOW BUMP despite running stiffer springs so that car doesn't pitch/dive to quickly.

    same for squatting motion ( but hey RF2 cars are already slidey/loose on rear so you don't have to worry about corner exit understeer lol ).
     

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