ACC Blog Assetto Corsa Competizione v1.8 dev blog

ACC v1.8

We’ve been working really hard for a long period of time to take the industry top level of ACC physics to the next level.
There’s a lot to talk and explain and feel and try and discuss… so I apologise in advance if the explanations are not enough.

400Hz physics engine!
Starting with the most beloved coffee table discussion. The physics engine frequency.
Fernando has been working a lot in order to improve our physics engine functionality to the core. The result is big multithreading optimisations and variable component tick frequency. So instead of having a monolithic physics engine that runs everything at a given frequency, we can now choose which part of the simulation needs a higher frequency and which one can do with lower updates.
The end result is that we can have a much more precise control of the resources needed by our physics engine and achieve better performances even at high load scenarios such as very high number of cars on the circuit. At the same time, the better multithreading division of “jobs” keeps the CPU occupancy lower and gives the rest of the game engine (graphics, sound etc) the resources needed to run smoother than before, greatly improving average and minimum FPS.
As described before, all these improvements while not directly raising the FPS count, they do permit the whole game to run smoother. We grabbed the opportunity instantly and after a few tests we decided to raise the frequency of our physics engine at 400hz!
All the critical components of the physics engine (tyres, suspensions, springs, dampers etc) as well as FFB are now updated at 400hz while not losing any measurable performance, even without using the latest fancy acronyms like DLSS and FSR.
The higher 400hz refresh rate, enhances the tyre collision detection with the ground even at very high speeds. At 250kmh the car moves 69 metres every second. This means that in v1.7 the tyre and ground detection would be updated every 21cm. Now in v1.8 the tyre ground detection occurs every 17cm at such high speeds. That’s a 20% improvement and it is significative. The result is improved and more detailed tyre to kerb simulation, improved springs and dampers interaction at higher rates, improved and more precise FFB refresh etc. etc.

Yes it is true that refresh rate is important up to a point but it is more important how many things you calculate and simulate at every tick. ACC has always been doing an amazing amount of calculations for every physics refresh update. Now it calculates even more data at an even higher refresh rate. We think you’ll like it.

Tyre model improvements
The updated frequency was already giving great results in the tyre simulation but we wanted to do more. One of the most difficult to research aspects of tyre simulation is the combined grip. The amount of grip available while a tyre undergoes both longitudinal and lateral forces at the same time. It is also an aspect of the tyre characteristics that greatly influences drivers feel, confidence and predictability.
We have completely rewritten the combined grip equations and values. The new simulation offers improved control right and over the limit in various conditions, improved trailbraking possibilities and more traction even without Traction Control electronics. The combined grip characteristics of each tyre are completely dynamic and greatly influenced by the type of surface they are rolling on, the wetness or lack of there of of the surface, the load, the vibrations, the pressure and of course the temperature of the tyre.
Speaking of tyre temperature, the heat generation, dissipation, and propagation has been rewritten from scratch. Our model is extremely complex, with many many variables influencing each other dynamically. ACC v1.7 had achieved already a high level of simulation but we really wanted to make a substantial improvement. In v1.8 the surface flash temperatures, which unfortunately but realistically you cannot check in real time HUDs, are even more dynamic than previously. This greatly affects the surface grip of the tyre, meaning that extremely aggressive inputs from the driver, or aggressive setups, can and will overheat the surface temperature of the tyres instantly.
The tyre characteristics dynamically change depending on the temperature which means you can expect a more nervous tyre at cold temperatures and more rubbery feeling at higher temperatures up to a “oily and vague” feeling while overheating.
Obviously the surface flash temperature propagates into the tyre core temperature but does so in a more realistic way. As a matter of fact, the tyres lose core temperature much slower and so you can position your car in the grid without having to wait for the last 10seconds. On the other hand, depending on the track you might need more than 3 to 4 laps to get precise pressure readings from core temperature. We didn’t even forget heat generation on extreme conditions. The model correctly handles such situations like burnouts and donuts. The surface will overheat greatly but it will not skyrocket instantly to temps that go way over 300°C and resulting in blown tyres. It will happen of course if you insist, but it will take a different effort.

We just getting started.
A new camber simulation that not only improves greatly the behaviour in extreme situations in both negative and positive camber values (like riding a kerb with the inner front wheel), but also offers much more realistic temperature generation and wear on Outside, Mid, Inside parts of the tyre depending on the camber values of the setup.
Use a highly negative value and wear the inner tyre in long distances, or use a low negative value and wear down the outside tyre. The new camber simulation also creates interesting 2 wheel riding moments, if you hit high kerbs with high CoG cars.
The camber simulation goes deeper, influencing also the forces generated by the big wide slicks when they ride longitudinal bumps and kerbs. The tyres now correctly generate important amounts of lateral forces in such conditions, provoking FFB forces that can affect your stability if you are approaching such road features with high negative camber and toe values.
Too annoyed by such behaviour? Lower the negative camber and tow and get more stability over such longitudinal features of the road, but at the expense of lateral grip and outside wear.
A new viscoelastic rubber friction model takes into account the change of tyre characteristics that occur at higher rotational speeds. Great control at low speeds and trickier behaviour at higher speeds.
Together with a brand new tyre vibration model relative to high slipangles and speeds, it results at the same time in a more dynamic model and better feedback to the driver as the tyre will be result smoother at lower speeds even over the limit, but will generate more vibrations at higher speeds even just above the limit, signalling to the driver either an imminent loss of control or tyre wear.
The vibrations are properly simulated on a physics level and are not FFB effects. They are also affected by tyre heat as a hotter tyre will generate more damping and lower vibrations.

Is that all? Nope, we’re not finished yet
There are many many more little details on the tyres simulation. Here’s a couple more.
Improved wet surface simulation. Slicks are death traps when wet but you can do some nice power drifts at low speed if you’re careful. Really bad aquaplanning at any slipangle at speed. Obviously better with wets but again aquaplanning is bad at wider slipangles. The wets temperature range is also widened but not necessarily better in terms of performance.
Improved slipangle/ratio simulation relative to cold and overheating tyres. Completely different characteristics now on the two temperature extremes.
Improved tyre flex and movements of the whole body relative to the flex. The best of you should feel the car rotating in yaw when the tyre flex is bigger (depending on pressure, temperature, surface etc. Try very low pressures, it’s “interesting”)
Improved pressure influence to heat generation. Lower pressure tyres generate more heat, higher pressure tyres generate less heat. While optimum pressure is still the target to achieve, you might want or forced to search some better compromises between the optimum pressure and the heat generation of the tyre. So playing with the pressures to bring heat up or down comes into play a bit.

Bumpstops
Tyre simulation is not the only area we improved. We have plenty new features and improvements on other areas as well.
New rubber bumpstops damping simulation. In ACC v1.7 the bumpstops are a very important aspect of the handling tuning and they work as progressive springs on top of the normal springs. V1.8 now properly simulates the rubbery self dampening nature of bumpstops. This means that you don’t have to compromise and overcompensate with normal dampers to take care of the bumpstop elastic rates. The dampening of bumpstops are now implemented for each car, greatly improving the behaviour of the car over kerbs and jumps. They also permit further fine tuning of the dampers and let the car bounce more naturally while absorbing bumps and kerbs in the meanwhile.
As an example, Lesmo 2 inner kerb is not insta-kill anymore. On the other hand, riding the inner Ascari right hander might be more problematic as the new camber simulation make the tyres follow the strange conformation of the kerb and destabilise the car.

Brakes
Brakes are more powerful and together with the new tyre flex can slightly make the rear end move a tiny bit under braking depending on the situation.
The Brake ducts simulation is improved and their influence in the tyre heat generation is now less. You can still use the brake ducts to heat up tyres but not as dramatically as before.
Driving style also makes quite a difference now. Aggressive drivers will need more open ducts to somewhat limit the tyres overheating, smoother drivers can work with smaller ducts. Especially in races.

Engine throttle
Improved engine throttle simulation. We now simulate the engine throttle valve better and the result is easier starts without stalling the engine. This enabled us to limit the range of the launch control speed to a very low number (like 5kmh and after that it disengages). The side effect is that you can spin the car around with better control without the launch control overrevving the engine. Obviously the different throttle simulation also affects the way your throttle modulation and engine response occurs.

Track grip on and off the ideal line
Improved track grip on and off the ideal line. The difference in grip is still present but less evident, making the choice of alternative racing lines and overtaking manoeuvres not only easier to handle but also more interesting, letting the drivers choose slightly different lines for different car configurations.

Temperatures and performance
Track temperatures and ambient temperatures have also been tweaked for improved simulation of various conditions. We also simulate night and early morning humidity and dew. This means that you cannot lower the temperature at the minimum in the night or very early in the morning and hope to obtain record laptimes. Your tyres will slightly suffer the dew and the performance will be worse even though the cold weather will improve engine power and downforce.

Conclusion
The lists goes on, as well as the list of cars tweaks and improvements (like Huracan corrected front steering geometry, Nissan and Lexus corrected rear bump steer and more and more).
With all those improvements in tyre characteristics, better grip sensation, better TC, better brakes, better engine response it’s normal to expect faster laptimes, which would completely void our quest for realism.
I’m happy to inform you that v1.8 laptimes are slower by an average half to two seconds depending car, track, ambient combination. And of course we are hard at work on a better BOP balance as always.

Graphics
Focusing on the updates related to graphics and gameplay (including what is relevant to Multiplayer and admins).
Let's start with Graphics Updated project to Unreal Engine version 4.26.2, which brings about a number of updates (some minor, some more noticeable) to the graphical art and camera behaviour in ACC:
- Revision of various track-related shaders to follow Unreal Engine version rendering changes.
- Revision of various car-related shaders to follow Unreal Engine version rendering changes.
- Skybox revision to suit Unreal Engine version rendering changes.
- Reduced bezel and SSR and SSAO artefacting appearing along the bezel lines in Triple Screen rendering mode.
- Updated TV, cinematic and free cameras to use the new Unreal Engine cameras with improved DOF effects - this is a global change, old cameras are deprecated.
- Updated CinemaHUD (F7 camera) to use the new and improved DOF effects.

And then the main ones:
- Added Nvidia Deep Learning Super Sampling (DLSS) 2.0 support for compatible GPUs (RTX 20XX series or newer). NVIDIA DLSS (Deep Learning Super Sampling) is a deep learning neural network developed by NVIDIA that increases graphics performance. DLSS takes a lower internal render resolution and increases the pixel count to a target resolution using AI processors on NVIDIA RTX GPUs, called Tensor Cores. Each DLSS quality setting defines the level of super sampling with different ratios of render and target resolutions.
"Quality" setting prioritizes image quality by rendering the game internally at the closest resolution possible to the target, while "Ultra Performance" prioritizes performance with the highest difference between the internal and output resolution.
In between, "Balance" and "Performance" settings aim for various levels of compromise between graphical fidelity and performance gain.
Using DLSS will override other anti-aliasing methods and their functions.

- Added AMD FidelityFX Super Resolution (FSR) support for all GPUs. FidelityFX Super Resolution is a spatial upscaler: it works by taking the current anti-aliased frame and upscaling it to display resolution, without relying on other data such as frame history or motion vectors, producing a high-fidelity image at a performance gain over traditional rendering methods. At the heart of FSR is an algorithm that detects and recreates high-resolution edges from the source image. FidelityFX Super Resolution is compatible both with AMD and NVIDIA GPUs. With no built-in anti-aliasing override, FSR can be combined with other TAA features.
Ultra Quality mode produces an upscaled image with quality very close to native rendering. It should be selected when the highest quality is desired.
Quality mode produces an upscaled image with quality representative of native rendering, with a sizeable performance gain.
Balanced mode produces an upscaled image approximating native rendering quality, with a major performance gain compared to native.
Performance mode visibly impacts image quality and is suited for situations where needing additional performance is critical.
Custom mode allows the user to customize the source resolution scale with complete freedom, including the ability to use native resolution (100%) or supersampling (higher than 100%) with the added benefits of FSR's proprietary sharpening method (RCAS).

Both DLSS and FSR are selectable and functional in Triple Screen and VR rendering modes. DLSS is both a sampling and antialiasing method, while FSR can be used in combination with regular upsampling (via custom resolution scale) and select Temporal AA solutions.

DLSS implementation includes a custom DLSS version (dll) by Nvidia made specifically for ACC.
- Added Temporal Antialising Gen5 option support. Offers improved aliasing and clarity at a moderate performance cost. Optional over the existing TAAgen4 and KTAA implementations. In addition, we have improved various graphical elements, such as the blurred rim shader and rainfall particles.

Gameplay and BOP
Adding Fanatec GT World Challenge Europe 2021 season as bonus content with all entries, liveries and drivers and championship season, including an updated BOP for participant tracks. - as with every season update, this adds a whopping number of new entries, liveries, drivers to choose from and a dedicated championship season.
As the largest gameplay-related addition, we are adding an "Open season" in Single Player, merging all game content into a "sandbox" season featuring grid customization, with opponent grid mixing option to Custom Race Weekend and Quick Race game modes.
You can use the grid mixing sliders to set car group prevalence in the grid. GT3 car group has an additional setting for preferred generation of opponent cars (all, pre-2019 or new-gen only).
- Added Open series championship mode with grid (car groups) and track lineup customization, with multiclass championships now splitting points per car groups.
- Automatically generated custom cars are now grouped into teams both in single-make custom mode and Open series championship, and we reworked the driver assignment system to support custom-generated grids and various driver count requirements.
Under the hood we also standardized the entry and team ID system across the whole game content in support of the Open series grid generation and championship.
The Open series will have its own BOP assignment (currently matching the 2021 season BOP), functioning as a moving BOP with the latest seasons. Most importantly it also serves as the basis of Multiplayer BOP. The previous Multiplayer BOP and track seasons will be deprecated, and the configuration will point to the one and only MP BOP, corresponding to the all-time Open series BOP. Obviously, individual official seasons remain playable in Single Player with no change to their earlier configuration and functionalities.
In addition, British GT and IGTC BOP will be updated to use the latest BOP data and DHE tyres when BrGT or IGTC-exclusive tracks are played through the 2021 season or the Open series (or Multiplayer). For season authenticity, the original IGTC and British GT seasons in Single Player continue to use the original 2019 BOP with the corresponding tyres that the original DLC packs recreated.
Multiplayer track seasons are now deprecated and all track configurations point to the Open series.
Note for admins: the old season suffixes in the server configuration will remain there for legacy functionality, but they will no longer create a difference in track/BOP version. Server track configuration (event.json) should use the non-suffix version in continuation, e.g. "misano" instead of "misano_20XX".

Note for users: no matter the server config, Multiplayer will always use the latest Open series configuration from Single Player.

Weather
Improved weather model:
variability (=randomness in MP) will now affect the variation and frequency of weather cycles:
- Higher variability will now produce larger variation and less predictability in the length of individual weather cycles (time between peaks).
- High variability might produce both fast changes or prolonged weather spells (or both combined) within the same weekend simulation, the variation capable of shifting it to either faster or slower changes.
- Low variability will produce more even weather cycles, akin to the pre-update model.
Overall it adds to our principle of reducing the predictability of weather patterns, which the old system had a tendency to produce even at higher variation.

The list of improvements in this version 1.8 is really long and goes well beyond this post and even the actual changelog.
We worked really really hard for ACC v1.8. Probably we should have called it ACC V2 and sell it full price, but you know the drill, this is Kunos. We just love driving. We hope we haven’t messed up things a lot and hope you will enjoy it.