AC, Developer comment, Video

Reality is so arcade (update)

In January, Aristotelis started to publish a series of “Real X vs. Assetto Corsa representation” videos in cooperation with his friend and automotive journalist Maurizio Spinali. Today we received the lastest combo with a little surprise: The showcased Audi S1 isn’t even available to Assetto Corsa yet.

Just in case you missed the previous ones: Alfa Romeo 4c, tuned KTM X-Bow R.

The highlight is that Aris starts to unleash the “rally soul” and does a few successful Scandinavian Flicks. As usual, the AC video almost perfectly matches the real footage – even on far-away physics corner cases.

Simulators usually (need to) focus on a range that they want to simulate, which doesn’t magically include corner cases. Assetto Corsa for example is damn good at racing pace, but doesn’t shine in slow driving handling. Cars can’t even stop inside the physics – with extremely low speed the car would suddenly stand nailed to the track and you need some serious and unrealistic effort to get it moving again. A different example is the Aero simulation; it’s quite sophisticated and realistic while you use a high downforce car “normally”. But as soon as your car jumps, it basically leaves the simulated area and stays airborne in a stable way. Real race cars will lose their ground effect and flip due to the downforce bias in the rear, some needed only a tiny bump and some slipstream.

I don’t want to say this is bad, as we are talking about corner cases that usually do not apply to driving in AC and it would have been a bad choice to invest effort here – my point is there are acceptable corner cases which aren’t well simulated without hurting the simulation aspect. Coming back to the video I’m asking myself if this also applies to the Scandinavian Flick and what it means that Aris could actually recreate it in AC.

I’m not convinced that the Scandinavian Flick is not just a really usual application of already well simulated physics, in fact it’s “just” some tyre load and weight shift physics. But this either means Assetto Corsa does simulate whatever is required very good and reacts realistically just by applying the correct numbers, or that the Audi was more or less modeled and forced to behave like this.


Of course I don’t have a clue what the answer is, but both cases would be fascinating. Somehow it seems unbelievable that you can have a sim that recreates such a behavior just by putting in the manufacturers data.

Very important note:

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See Aristotelis’ comment below!

3 thoughts on “Reality is so arcade (update)

  1. Hi, thanks for your nice article.
    Allow me to point out some inaccuracies, if I may.

    The so called “slow speed” physics is one of those urban myths, but the truth is a bit different. The slow speed physics engage on speeds under 2-3km/h simply because you can’t divide by zero(speed) on the equations we have. So at very very VERY low speeds (under 2km/h) the physics switch to a more simplified model to just stop the car and keep it stopped. We have also worked to have the car bounce properly on its suspension while stopped now. This wasn’t the case in the very early versions of AC.
    Also, the new clutch simulation permits pretty smooth starts if you want to use the clutch pedal. Unfortunately, one of the biggest advantages of reality is that the G forces play a very very important role in releasing the clutch. It’s amazing how our brains work to keep clutch and accelerator working together and make a car start smoothly. In a sim, infront of a monitor you miss all those g force feedback and in such a delicate situation as starting smoothly with a clutch it is often a disaster. Try it though, it takes some practice, and you’ll see you can start very smoothly in AC too.
    What we also do when the car is stopped is applying a bit of braking force. We do that to not let the car slid away on slight slopes (remember our tracks are laser scanned so it’s hard to find a really flat piece of ground). There are many reasons why we choose to do that, amongst various even to protect hardware as a car sliding and maybe hitting a wall or opponents, could give high vibrations and violent movements to the latest generation of force feedback steering wheels. There are many little things that a developer has to think of, that might seem stupid or lazy to the normal user, but I digress.
    Fact is, there is not a single one situation while driving, when AC is not using it’s realistic physics engine, except when you’re practically stopped.
    You can also drive at very normal “street legal” speeds in AC with proper behavior, but beware of what you think is normal speed in a sim. One of the biggest mistakes that people do on sims, in front of a monitor is to underestimate the speed they are going.

    Aerodynamics is also always working, no matter what height, even if the car jumps. Aerodynamics in AC are so advanced that we even simulate the density of air depending on the ambient temperature so to speak…
    Real car manufacturers work really really hard to avoid such incidents like the Porsche one you have posted. There are now even regulations that force manufacturers to place aerodynamic devices that try to avoid such incidents. On the other hand, you can perfectly simulate this jumping flip in AC. Only thing you have to do is to input the appropriate physics values in the aerodynamic section that simulate the bad aerodynamic behaviour at certain angles.
    The fact that you see cars jump and “fly” level in AC, is because the real cars are usually setup in a way to do so. Here’s an anecdote. The original setup of the Glickenhaus SCG003 was provoking a front end lift up. The engineers worked really hard to avoid this during the race. But if you try the car with the default setup, you have the same effect. Have a look on this thread:

    When we test real cars and compare with the sim, we don’t have any doubt that physics work on any situation. What we try to find out and correct as much as possible, are situations where the real car reacts differently than the sim. That’s why we try the cars well over their normal grip limit where the most “unknown and undocumented” physics behaviours happen.
    And yes, modesty apart and believe me, no marketing bullshit talking here, AC does simulate really really well what a car does, even at the most extreme situations.

    Thanks again cheers.

    Liked by 3 people

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