Suspension: rear ride height

Discussion in 'Car Modding' started by lonestar29, Sep 28, 2018.

  1. lonestar29

    lonestar29 Member

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    When working on a setup, I sort of expect that increasing ride height in garage (static condition) would result in a ride height increase at speed. But one mod I am driving has me puzzled, and so I am seeking enlightenment on what i am not considering.

    I ran 11 test runs collecting telemetry with DAMplugin (thanks Lazza)... each run was 1 lap, and in each run, i changed only the rear ride height (charted below on x-axis in millimeters). And the y-axis is the rear ride height at the end the lap on long straight ... when i reached 300 kph.
    RearRideHeight.png

    In small increments, I increase rear ride height in the garage, but at top speed the rear ride height continues to drop. It did not start going back up until i went above 85mm initial rear ride height.
    No other parameters were changed. Rear spring was constant.... and took data point at 300kph to ensure consistent aero conditions.
    Also, through all these tests, the front ride height was consistently 40-41mm.

    I understand how increased rake could offer increased aero forces (diffuser or body), but that doesnt seem to explain these results...

    Any thoughts?
     
  2. Lazza

    Lazza Registered

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    I won't claim to understand how it works (I've been told but can't remember), but in rF2 when you change the ride height it's not the only thing that gets changed. @lordpantsington was always a good one to ask about it, others would know too. It was said around a year ago (maybe less) that this ambiguity around setup changes and the actual effect (like the lack of a live ride height to see what your changes are doing) was something they (S397) were hoping to change, I'm hoping they meant with the new UI.

    So I would say your results reflect the fact that your single change isn't actually applied as a single change, and it's only when you get to extreme levels that it's having the expected effect.
     
  3. davehenrie

    davehenrie Registered

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    Adding to Lazza's thoughts, the increased rake is probably increasing downforce. You may have to increase your rear spring rate to compensate.
     
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  4. lonestar29

    lonestar29 Member

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    @Lazza
    The possibility that other things are changing, does help explain what is happening. I guess I am wrong to asssume that all other parameters are constant.
    Based on what I am seeing, its likely that the effective spring rate is changing as a variable to initial rear ride height setting.
     
  5. bwana

    bwana Registered

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    Does adding rear packers make a difference ?
     
  6. lonestar29

    lonestar29 Member

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    @bwana
    rear packer was set to max during the test... but at end, i did a little test to assess the effect of the packer.
    The data suggested rear ride height at 300kph wouldn't drop below 24-25mm, so I thought maybe that was related to the packer.
    I set initial rear ride height to 81mm (in garage) and removed packer... ran a lap, and was surprised that there was not discernible impact to rear ride height.
     
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  7. lonestar29

    lonestar29 Member

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    maybe it was already as low as it could go? my curiosity though with primarily with what rear ride height was doing...
     
  8. lordpantsington

    lordpantsington Registered

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    Isn't it possible to log Aero forces? Can't tell anything from your graph other than it looks like you are riding the bumpstop @ 24-25mm. Need more info to determine why. If you can dig into the Aero settings in the HDV that should help.
     
  9. lonestar29

    lonestar29 Member

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    @lordpantsington unfortunately mod is encrypted so i cannot scrutinize the HDV or suspension file.
    Here are the aero forces overlaid on second axis... which seems to rule out aero as being significant to this phenomena.
    seems to put spotlight on suspension geometry?

    rideheight_aero.png
     
    Last edited: Sep 29, 2018
  10. lordpantsington

    lordpantsington Registered

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    FWIW I'm looking at this as your first test is @ 100mm and you have been decreasing static RH in steps. If the expectation is that decreasing the SRH results in decreased RH at speed, then yes, your graph shows that happening (quite linearly). It also shows the RH at speed following the same trend as Aero forces.

    Assuming your aero forces are high enough to get onto the bumpstop with any SRH, more available compression=more used.
    If you look at (Static Ride)-(Ride at 300kph), you can see increasing static ride height directly translates into more compression stroke before bumpstop. I estimated compression stroke (low SRH to high) as: [26,32.5,41,47.5,53,55,57,57.5,60,61,62]. So why does that level out, and decrease from high to low? My guess is: it is following Aero (flat spot is also in the area of lesser forces), and the compression stroke is being limited at low ride heights. Basically it is going as low as it can go. If you ease up on Packer (use none) you might see Static Ride Height @ 60-78 mm drop more.
     
  11. Lazza

    Lazza Registered

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    @lordpantsington He went the other way, starting at 60mm SRH and increasing, but the direction is of little consequence here since each test is independent :)

    The puzzle is why RH @ 300km/h drops with increasing SRH, then stabilises, then increases again. The small deviation in aero forces seems to me more a result of the ride height than its cause.

    I recall that when, say, softening rear springs only, the spring rate isn't actually the only thing changed because the ride height is also being maintained (obviously if you take a car and only change the springs, even your SRH will drop, but the SRH is part of the setup in the game so other changes are made to maintain it). It's in my head that these ancillary changes will change the behaviour of the suspension under varying loads in a way that might explain the behaviour described above, but it's all very fuzzy to me so I could be wrong.

    Is it possible that by changing RH only, the suspension is modified in such a way that it is more compliant under load, until it hits some sort of barrier (perhaps bumpstops) at which point the increasing RH then starts to have a more linear effect you might otherwise expect from the outset?
     
  12. lonestar29

    lonestar29 Member

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    Exactly... that is the puzzle on this mod. All setup parameters remain constant (spring, wing, etc)... so I am only increasing SRH. I would expect spring deflection to be similar for each run... but its not.
    Starting at SRH = 60mm . . . the RH@300kph is 34mm (So rear spring deflection cause rear to drop 26mm).
    Now increase SRH = 70mm . . . the RH@300kph is now 28mm ... so this time, the rear has dropped 42mm. what is going on? Mass of car is same, Aero loading is same, the spring settings are the same. What causes the spring to deflect more.
    I know this is overly simplistic... but this is what i am visuallizing... but maybe the spring is an angle less than perpendicular...
    Screenshot 2018-09-29 at 21.42.45.png
     
  13. patchedupdemon

    patchedupdemon Registered

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    Your changing the angle of attack of the rear wing, surely that has something to do with load placed upon the suspension at speed

    Edit just realised you’re saying the aero loading is the same, so if I’m reading that correctly, it doesn’t make sense, because the type of angle of attack change increasing rake has, you’d expect both drag and aero load to change
     
    Last edited: Sep 30, 2018
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  14. lonestar29

    lonestar29 Member

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    @patchedupdemon correct... increasing rear static ride height (SRH) does increase rake in garage... but the rake is not maintained at higher speeds.
    still, the puzzle is why does the effective spring rate change so much as rear SRH is changed?

    AFAIK, the rfactor suspension model is limited to 'push rod' only?
    PushrodSpindle=(x,y,z) // spring/damper connection to spindle or axle (relative to wheel center)
    PushrodBody=(x,y,z) // spring/damper connection to body (relative to wheel center)
     

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