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How to adjust setups for GT3s in v1.9?

Discussion in 'Chit Chat Room' started by Strummer, Oct 28, 2016.

  1. Strummer

    Strummer Simracer

    Aris has already said they are ~1-2 sec slower per lap in 1.9. I can certainly confirm this: my lap times at Mugello in the 488 GT3, previously in the top 25 on RSR for this combo, are now a full 2 sec slower. Aris suggests adjusting setups but where to start? I've worked hard on my 488 GT3 set, so all advice would be gratefully received.
     
    deni80s likes this.

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  3. Kade

    Kade Hardcore Simmer

    Try decreasing negative camber (as in go towards positive) from both front and rear.
     
    Diablo_rf likes this.
  4. Strummer

    Strummer Simracer

    Many thanks.
     
  5. magzire

    magzire Alien

    I don't think camper setting would cost 2 secs?
     
  6. Strummer

    Strummer Simracer

    I wish I knew what's responsible for slowing the GT3 cars down but I'm no setup expert, therefore my own take a long period of trial and error to get right. If it's just extra grip from the new tire model, perhaps less downforce will do it. I think I also read somewhere that ride height has been raised but I'm not sure.
     
  7. Kade

    Kade Hardcore Simmer

    Afaik GT3 field is slower in general and you won't get all the pace back. I suggested camber change only because there's was a change in inside tyre behavior and grip per axle should be less dependent on outside tyre now.

    Tyre pressure should also affect the tyre temp more so keep that in mind if you operate below 80c or above 105c.
     
  8. Diablo_rf

    Diablo_rf Hardcore Simmer

    I was testing the 488GT3 on SPA yesterday for about 4 hours, my previous time before the patch was 2.18.567 (actually not the best time because I didn't do that much of driving back then).
    Well, the first thing I've done is set the setup to default and did 10 laps, couldn't get better then 2.20.xxx, after that I start testing. Found that the default stiffness of the springs are too hight/stiff, lowered them to what was default on previous patch, 90/105, and also lowered the car to 55/63 ΠΌΠΌ , did another 10-15 laps, time 1.19.5xx, better, but still very off pace.
    Next I tried to lower the camber, from 3.60 to 3.20 for front and from 3.4 to 3.2 to rear and now my time was 1.19.2xx, not bad, car feels like it had more grip in the corners then with higher camber.
    After that I was pushing and pushing, and couldn't go lower 1.19.xxx.
    Next step was adjusting the ARB, tried different settings but all felt strange, what I did is I set them all to maximum, fron 15 and rear 10 (if i'm right). Also increased the rear first rebound from 6 to 10-11. All this changes made the car a bit understeer, but also more stable in the high speed corners, which allow me to carry more speed.
    So at then end I got 1.18.580, almost the time I had before the patch, even considering back then I didn't setting it too much, could go faster.

    Well, still not very happy, would like to get some advice from the guys that are better tuners than me =)
     
    Last edited: Oct 28, 2016
    Ernie and NetracingEurope.org like this.
  9. Well I did an hour stint today at Nurburgring Gt and regardless of setup changes I am still 1.5 secs slower. It really seems that you have to wait a split second longer to start accelerating out of the corners or you get understeer. The car feels great, but it just seems that there isn't as much grip as before. Is this what your experiencing as well or are you seeing other issues.
     
    Last edited: Oct 28, 2016
  10. Diablo_rf

    Diablo_rf Hardcore Simmer

  11. Georg Siebert

    Georg Siebert Simracer

    Believe I can help you with this,
    the 488 GT3 has inherently more understeer than other cars in its class, an attribute which got only amplified with the new v10 tyre model. The new tyres feel stiffer, have a more detached road feel, loose grip with slip angle sooner and a pressure varience (e.g. due to temperature rise and fall over a lap) has less of an effect on response and handling of the car. On top of all that, the downforce of the 488 GT3 was nerfed, so less aero grip as well. Let's go through some remedies, shall we.

    Setup adjustments in order of importance/effect on car
    1) spring rate & ARB
    2) tyre pressure
    3) camber & toe
    4) aero
    5) dampers
    6) differential & electronic aids
    7) others

    Pre-flight checks
    - make sure to have ENABLE_DEV_APPS=1 in system/cfg/assetto_corsa.ini
    - enable car engineer
    - enable aero app

    Spring rate & dampers
    - the default spring rate with 130 kN/m on the front is too much for a mid-engined, mid-downforce car like this, a higher spring rate in the front just increases the car's understeer -> lower it to 110kN/m, we get a nice 3.3Hz/3.2Hz ride frequency distribution between front & rear axle
    - the four damper values below are damping ratios, the ones for the front axle are accurate, the ones for the rear are not (a timeless bug it seems)
    - a damping ratio of 1 equals critical damping, the 488 has a 'normal' damper layout, so we want to stay below a ratio of 1
    - we want the front rebound to be higher than the bump, that helps agility and transient response (S-curves, Les Combes)
    - as mentioned, the rear ratios are wrong, if the damping ratios (front & rear) lie between 0.5 and 1, the correction factor is 0.25, if the ratios are higher than 1, the correction factor is higher as well, so it is not constant (not intuitive, I know)
    - so at default the front bump ratio is 0.87, the rear displays as 0.81 - the correct rear bump ratio is then ca. 1.15, hence too much
    - so increase rear rebound, decrease rear bump and increase rear rebound to bring it in line with the rear bump

    [​IMG] [​IMG]

    ARBs
    - since the actual value is not displayed, this limits our understanding and recommendations of this item
    - suffice it to say, a one click adjustment on the front ARB has a higher effect on handling than one click at the rear on this car, this applies to GT3 cars in general
    - since we decreased the front spring rate, we have to compensate with +1 ARB_FRONT to retain the absolute roll stiffness and its distribution between the front and rear axle
    - if the car still understeers, then increase ARB_REAR

    Tyre pressures
    - the optimal pressure for GT3 tyres (even in v10 as far as I can tell) is 33 psi
    - as anecdote, was driving a custom GTLM car on Spa yesterday for which optimal pressures are 35 psi, difference between 33 and 35 psi on this car was 0.7x seconds a lap
    - the default cold 25 psi should rise to the desired 33 at 80 degrees, if front or rear tyres are below that through most of the lap, increase pressures accordingly

    Height
    - set ride height to lowest possible, to 0, you won't have issues with the minimal requirement
    - benefits: a lower cg for faster transient response, a slightly higher CL (coefficient of life (freudian slip, lift)) from front splitter and diffuser
    - the actual ride height is not the one displayed in the car status, look for it in the aero app, GH (ground height) in yellow for front splitter and diffuser
    - the actual collider of the car model has a seperate height value from the cg, in the physics files

    Aero
    - at the bottom of the aero app, you'll find the sum of the lift & drag coefficients and the total downforce and drag values in kg
    - the calculations of this app only work during driving and not during replays
    - an increased AOA (angle of attack) of the front splitter has nearly no drag penalty, for maximum downforce adjust only the rear wing for the following point:
    - look at %@front, have it between 46 and 49% for a balanced aerodynamic load on the front and rear, anything above 50% is inherently unstable, this value will fluctuate whilst driving, so make some screenshots to look at it more closely on the desktop

    Camber & toe
    - the default rear toe is way too positive, resulting in more understeer - I personally am a big proponent of toe values of 0, a seperate topic, so take these as you like
    - set toe to or close enough to 0, better to have it positive than negative at the rear, +/- 0.02 radiants in the front are ok
    - as mentioned above, the grip decreases with increased slip angle slightly sooner in the new v10 tyre model than with v7, so make the static camber angle a bit less negative as pictured below
    - static camber, because the camber angle fluctuates during cornering - more negative camber leads to a higher slip angle (see suspension app, purple SA value for more details)
    - in general, anything more negative than -3.4 degrees is too much for these GT3 tyres (v10, v7, v6)

    [​IMG]

    Differential
    - lower DIFF_COAST to 40% for more turn-in, if unstable under braking increase to 50%

    Traction control
    - the default setting when you load the car is not setting 1 on the traction control list
    - TC is defined in the physics files as slip ratio limit, say 0.11 - hence if this ratio is reached, the TC will kick in - the higher the TC setting (CTRL+T), the higher the slip ratio limit, the less restricting it is
    - increase TC, if you have understeer out of corners - a too high setting will result in oversteer of course
    - all above points apply to ABS as well


    That's it for now, have at it.
    Gonna make some food now, tortelloni with broccoli and zucchini.
     
    Last edited: Oct 29, 2016
    hazardic, acespizee, baboon and 37 others like this.
  12. Kade

    Kade Hardcore Simmer

    I'm curious why you prefer higher ride frequency on front than rear?
     
  13. Georg Siebert

    Georg Siebert Simracer

    @Kade
    It should say 3.2Hz/3.2Hz, just like in the right picture for adjusted values.
    Also the last line in springs & arb section should read
    - so increase front rebound, [...]

    If ride frequencies are within a margin of +/- 0.1Hz of each other that's totally fine. The step in front spring rate is often only 10kN/m and 5kN/m at the rear for most Kunos' race cars, so sometimes per calculation with a best guess CG you come up with a rate of xx2.5, so you have to choose between xx1.0 or xx5.0 then anyway.
    Theoretically, the rear frequency should be slightly higher than the front, for the rear' oscillation to catch up with the front, but would necessitate compromises in other areas during practical use on the track.
     
    matz_AUT, baboon, deni80s and 3 others like this.
  14. Radfahrer

    Radfahrer Hardcore Simmer

    Thank you, Georg, for explaining all this very valuable stuff !

    +1 electronic pasta donated :)
     
  15. Kade

    Kade Hardcore Simmer

    Yes, rear ride frequency should be higher to achieve "the catching effect". That and the fact I often see stock setups on aero cars having higher front frequency by default made me want to know why exactly?

    More info about catch-effect can be found here if someone is interested: http://www.optimumg.com/docs/Springs&Dampers_Tech_Tip_1.pdf

    Also, I haven't found any good source how damping affects the preferred ride frequencies. If you happened to know more about this, I'd gladly learn more. ;)
     
    deni80s likes this.
  16. Diablo_rf

    Diablo_rf Hardcore Simmer

    @Georg Siebert Thank you for advice!
    I always struggling in understanding the right values of Camber on different track. I know that exceeding that limit or being below will force the tyre too loose the grip in the corner, but how do I know which value should I have for different tracks?
    Also about ARB, is this a setting which should be tunned on every track, or you just set it once and forget about it?
     
  17. mESCx

    mESCx Simracer

    Wow, you got 1 minute faster just because of setup?:D
     
  18. Diablo_rf

    Diablo_rf Hardcore Simmer

    @mESCx Lol =) Unfortunately I can't edit that mistake =) I meant 2.18.580 =)
     
  19. Nice work Georg and Kade really informative.
     
  20. Emerson

    Emerson Racer

  21. Diablo_rf

    Diablo_rf Hardcore Simmer

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