1. Do you need support for Assetto Corsa Competizione? Please use the proper forum below and ALWAYS zip and attach the WHOLE "Logs" folder in your c:\users\*youruser*\AppData\Local\AC2\Saved. The "AppData" folder is hidden by default, check "Hidden items" in your Windows view properties. If you report a crash, ALWAYS zip and attach the WHOLE "Crashes" folder in the same directory.
  2. FOR ASSETTO CORSA COMPETIZIONE: If you report issues with saved games, please always zip and attach your entire User/Documents/Assetto Corsa Competizione/Savegame folder!
  3. If your game executable is missing, please add your entire Steam directory to the exceptions in your antivirus software, then run a Steam integrity check or reinstall the game altogether.

PHYSICS Chassis flex

Discussion in 'ACC Blog' started by Aristotelis, Dec 17, 2019.

  1. Aristotelis

    Aristotelis Will it drift? Staff Member KS Dev Team

    Assetto Corsa Competizione v1.2 introduces chassis flex simulation.

    In the past, Kunos has intentionally avoided the feature, with yours truly being openly and on the record on interviews, that an implementation of chassis flex was out of the question in our simulations. It wasn’t a knowledge limitation nor a lack of will to implement such feature, but a honest admittance that we didn’t have enough data to implement such a complex feature and we didn’t had the experience to know how to judge if said data and implementation would work properly or not.
    Luckily for everybody, the Kunos team is always searching to improve the level of simulation and Fernando Barbarossa wouldn’t take a “can’t be done” for an answer. Many hours of paper study, telemetry analysis and placebo tests (yes we do that to our selves… it keeps us on our “toes”… ) we proudly present you the first implementation of chassis flex in ACC!

    Chassis flex alone as a term is very generic and includes many situations and effects, that influence differently the vehicle’s handling. The actual monocoque chassis flexes, roll-bars can be structural or not and can flex too, engines and drivetrains might be structural or semi-structural and also flex, suspension points on the chassis can flex and suspension arms do flex. There’s a lot of flexing, bending and vibrations going on into a vehicle and obtaining data and simulating in real time, as well as understanding how each one of them influences the handling, can be pretty much impossible.

    ACC chassis flex simulates the amount of twist in the chassis and it is called torsional rigidity. They say an image is worth a thousand words and in this case, this little animated gif of a Formula car, explains perfectly the kind of flex we simulate.
    During cornering, braking and acceleration, forces from the tyres are transmitted to the suspension and successively to the actual body chassis of the car. Additionally all the surface undulations, bumps and irregularities are also transmitted to the suspensions and chassis. Ideally the chassis should be infinitely rigid so that the suspensions are solely responsible for the weight shift and geometry dynamics as well as absorption of bumps. In such way, changes to the suspension setup and configuration, would provide predictable results.
    Unfortunately there is no such thing as infinite rigidity in reality, on the contrary, because of material characteristics, weight limitations, safety, manufacturing limitations and economics and more, car chassis are quite a bit flexible. Nevertheless, modern manufacturing technology and techniques have greatly improved the rigidity of chassis. On top of that and especially in racing car chassis, data analysis and better knowledge of vehicle dynamics, have embraced chassis flex and use it, up to a point, as a handling advantage.

    ACC chassis flex is not a fixed value, but varies from car to car and is also influenced by weight distribution and car characteristics. The results in car handling and performance are subtle, more qualitative than quantitative. You might or might not appreciate the effects, depending on your sensitivity and driving style, that is to say it is not a night and day difference, although we do believe it is an important step forward in many different driving situations.
    More specifically, the most noticeable improvement is even better kerb handling. High transverse kerbs like Monza’s chicane ones, still shouldn’t be attacked, but at least the car will jump a little less and you have better chance of not losing control. Generally kerbs and bumps are absorbed not only by the suspension but also by some chassis flex. Some cars will take more abuse, others that have much more chassis rigidity, might be more upset. On the other hand, the chassis flex is very low dampened, so any vibrations remain relatively uncontrolled and can be felt as oscillations even after the initial cause. For example you might take a bump at high speed, the suspension will absorb part of the energy but some of it will make the chassis flex and oscillate. While the suspension might end it’s oscillation fast enough, you will feel another couple or so of oscillations of the chassis. If the suspension is not well enough damped, it might also go into resonance with the chassis oscillations and make the suspension also oscillate and influence the tyre loads.
    Chassis flex also influences handling response and precision. If we have a car with infinite rigidity take ”set” at a specific turn, meaning that it has finished it’s initial weight shift and rolling and is turning at the limit, any driver extra input might break the tyres peak grip and provoke sliding manifesting as understeer or oversteer without much possibility of correction. This is also one of the reasons why in reality, extremely rigid race cars feel “edgy” and require total determination and precision. If the chassis has some flex, possibly in a controlled range, then some driver input will both return some feedback and generate smoother loads to the tyres, permitting them to work around their peak grip and giving the driver the feedback needed to ask from the car some extra work. Obviously this kind of “flexibility” (pun intended?) comes at a price. While the driver will be able to ask more from the car handling and obtain some tiny extra even at the limit, on the other hand it will lose precision as the car might follow a line that wasn’t exactly what was required. This might force the driver to work harder with the steering wheel and give more small steering inputs in order to point the car correctly.

    As a rule of thumb;
    • The stiffer the chassis, the more precision and fast response the driver can obtain but the less willing the car will be to change its set and possibly react also badly on the edge.
    • The softer the chassis the more feedback the car will give to the driver, regarding its handling but also less precision and slower response with a general sluggish feel.

    Finally the different chassis characteristics also require different setup range to make the car work better.
    • A less rigid chassis will require softer springs and good damping in order to have the suspension to absorb most of the tyres energy and control the movements of the suspension afterwards, without triggering excessive chassis oscillations. Trying to use stiffer springs to regain precision, will only result in oscillations and vibrations that will stress the tyres and lose grip.
    • Stiffer chassis can handle both soft and stiffer springs but the stiffer suspension will offer a much more precise handling, fast response and predictability at high speeds. At lower speeds though the car might feel light and nervous, losing speed and traction. A small compromise might be needed, but expect to use stiffer suspension on cars with stiff chassis.

    The big advancements in aero, suspension, drivetrain and tyres simulation of ACC, combined with the precision of our laser scanned circuits, permitted us to use real setups and being able to compare real telemetries to the ones generated from the simulator. Feedback from the real drivers, their engineers and manufacturers further confirm the improvements of the physics engine. The chassis flex implementation is based on the solid basis of all the above and brings the real life to simulation comparison one step closer again. As always, we stay committed to hardcore simulation and we keep working to improve.

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  3. LucaBenj

    LucaBenj Racer

    TNX!!!!!! Guys, thank you! One more step forward in the simulation!
    Last edited: Dec 17, 2019
  4. D.Jankovic

    D.Jankovic Alien

    Amazing stuff... i remember watching that video and it was like Chasis flex will not be happening couple months of Aris being quiet bammmm surpriseee!!
    SimGuy_1, Soldier_003 and Ensi Ferrum like this.
  5. trasgu

    trasgu Simracer

    Very impressive work guys!, I was expecting this kind of features in your next sim when more powerful CPU's will be available. Aris, the chassis flex in the longitudinal direction is also simulated or it only is simulated in the lateral direction?.
  6. Aristotelis

    Aristotelis Will it drift? Staff Member KS Dev Team

    Only torsional for now, as in the animated gif. We're looking into the longitudinal
    Fremen_78, AurusCE, trasgu and 9 others like this.

    GRFOCO Alien

    Hi Aris.
    Will this affect also the (already) drive train flex?
    I mean, do the drive train flex will be more noticeable?
  8. Luis Branco

    Luis Branco Alien

    Congrats for the research and implementation of such a detailed feature.
  9. Gopher04

    Gopher04 Simracer

    @Aristotelis anychance you could give some idea what cars you would say have less rigid chassis and a stiffer chassis please.
    SimGuy_1 and peregrine7 like this.
  10. I had accepted that this would have never been implemented in ACC.
    I don't trust you anymore. You can even do what you think you can't ever do.
    You are super people. I'm honored to use your simulator.
  11. Maciej Malinowski

    Maciej Malinowski Hardcore Simmer

  12. CrimsonEminence

    CrimsonEminence Simracer

    Uhm, is it placebo, or is my wheel not as violent anymore, when attacking kerbs on T1 exit on Silverstone? Also Maggots, Becketts, Chapel is less "slippy", when "cutting" over these kerbs there. (2019' 488 TC->3 TC2->2)

    Spa on stormy conditions also was drivable af, except the usual Aquaplaning spots :D

    I can catch the car better, after having a highspeed collision with AI, this was definitively not placebo, i felt, where the "right" countersteering position of the wheel was and it sticked again.

    What ever you've done, it is more fun!
  13. VoodooChild

    VoodooChild Gamer

    you guys are amazing and keep on giving, you got a diamond of a game and keep on polishing it.
    as a user/customer, i truly feel blessed.
  14. n1lyn

    n1lyn Racer

    I'll give it some intense testing for sure. great stuff aris
    Salvatore Amato likes this.
  15. Would love a list of soft and hard chassis
    Firmi, KmikzPat, Piret2000 and 5 others like this.
  16. saurohd

    saurohd Gamer

    KmikzPat likes this.
  17. bratt01

    bratt01 Gamer

    From about 2 hrs of testing in the Aston at Paul Ricard - my setup pre-update was a bit stiffer than my setup post-update. My pre-update setup is quite a bit twitchier than my post-update setup.
    To get close to the same feel from the car I had pre-update, I had to soften springs all round, and do some damper work for kerbs too. It is still not where it was before but getting closer.
    Could mean the Aston is less rigid, as it doesn't like the stiffer setup I used before the patch. Some more testing is required.
  18. trutya

    trutya Simracer

    i tested the 2015 Lambo on Paul Ricard, but just for a couple of laps. loading the original setup, the car just staggered, felt very sluggish... then i stiffened dampers, lowered steering lock and it felt better. but the overall behaviour was easier to handle, i could feel the limits better and could control it more, especially in fast corners.
    need to get used to it but it's exciting.
    hope i'll have time to dig in deeper and start a full race weekend to see everything
  19. VoodooChild

    VoodooChild Gamer

    had some races yesterday with the 720gt3 setup i'm preparing for tomorrow's RLM league race in silverstone.
    despite the alleged BoP nerf, i could do about the same (admittedly slow, but that's on me) laptimes, push harder for longer and - most importantly - i was able to save the car when i cocked it up a couple of times or five.

    ACC is in a fantastic spot now, I hope everybody will spread the word because the game deserves a gigantic playerbase.
  20. saurohd

    saurohd Gamer

    Hi, what's your best lap time? i'm in the same situation and i would be know if i am to slow!!!! (congrats for your nikname!!!)
  21. VoodooChild

    VoodooChild Gamer

    well it depends on the track conditions (i think it was "fast" in that moment), i was about the 2 minutes mark and aliens were 2 seconds faster, but i suspect they weren't really pushing hard or they had some traffic.

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